senior curricululm 2014 - 2015 (volume - 1)

CHIEF ADVISOR

Ms. Anita Satia, Director, SCERT

GUIDANCE

Dr. Pratibha Sharma, Joint Director, SCERT

ACADEMIC CO-ORDINATOR AND EDITOR

Ms. Sapna Yadav, Sr. Lecturer

CONTENTS

S.No. Content Page no.

1. Syllabus - PHYSICS (Code No. 042) 1-17

2. Changes in Physics Syllabus for March 2015, Examination

18-19

3.

Delhi State Science Teachers’ Forum 20-28

4. Delhi State Science Teachers’ Forum 29-50

5. PHYSICS CLASS-XII SAMPLE PAPER-1 51-74

7. PHYSICS (Code No. 042)

Senior Secondary stage of school education is a stage of transition from general education to discipline-based focus on curriculum. The present updated syllabus keeps in view the rigour and depth of disciplinary approach as well as the comprehension level of learners. Due care has also been taken that the syllabus is comparable to the international standards. Salient features of the syllabus include:

Emphasis on basic conceptual understanding of the content.

Emphasis on use of SI units, symbols, nomenclature of physical quantities and formulations as per international standards.

Providing logical sequencing of units of the subject matter and proper placement of concepts with their linkage for better learning.

Reducing the curriculum load by eliminating overlapping of concepts/content within the discipline and other disciplines.

Promotion of process-skills, problem-solving abilities and applications of Physics concepts.

Besides, the syllabus also attempts to

strengthen the concepts developed at the secondary stage to provide firm foundation for further learning in the subject.

expose the learners to different processes used in Physics-related industrial and technological applications.

develop process-skills and experimental, observational, manipulative, decision making and investigatory skills in the learners.

promote problem solving abilities and creative thinking in learners.

develop conceptual competence in the learners and make them realize and appreciate the interface of Physics with other disciplines.

PHYSICS (Code No. 042) COURSE STRUCTURE

Class XI (Theory) (2014-15) One Paper Time: 3 hrs. Max Marks: 70

No. of Periods Marks

Unit I Physical World and Measurement 10

23 Unit II Kinematics 24

Unit III Laws of Motion 14

Unit IV Work, Energy and Power 12

17 Unit V Motion of System of Particles and Rigid Body 18

Unit VI Gravitation 12

Unit VII Properties of Bulk Matter 24

20 Unit VIII Thermodynamics 12

Unit IX Behaviour of Perfect Gases and Kinetic Theory of gases 08

Unit X Oscillations and Waves 26 10

Total 160 70

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Unit I: Physical World and Measurement 10 Periods

Physics - scope and excitement; nature of physical laws; Physics, technology and society.

Need for measurement: Units of measurement; systems of units; SI units, fundamental and derived units. Length, mass and time measurements; accuracy and precision of measuring instruments; errors in measurement; significant figures.

Dimensions of physical quantities, dimensional analysis and its applications.

Unit II: Kinematics 24 Periods

Frame of reference, Motion in a straight line: Position-time graph, speed and velocity.

Elementary concepts of differentiation and integration for describing motion, uniform and non-uniform motion, average speed and instantaneous velocity, uniformly accelerated motion, velocity - time and position-time graphs.

Relations for uniformly accelerated motion (graphical treatment).

Scalar and vector quantities; position and displacement vectors, general vectors and their notations; equality of vectors, multiplication of vectors by a real number; addition and subtraction of vectors, relative velocity, Unit vector; resolution of a vector in a plane - rectangular components, Scalar and Vector product of vectors.

Motion in a plane, cases of uniform velocity and uniform acceleration-projectile motion, uniform circular motion.

Unit III: Laws of Motion 14 Periods

Intuitive concept of force, Inertia, Newton's first law of motion; momentum and Newton's second law of motion; impulse; Newton's third law of motion.

Law of conservation of linear momentum and its applications.

Equilibrium of concurrent forces, Static and kinetic friction, laws of friction, rolling friction, lubrication.

Dynamics of uniform circular motion: Centripetal force, examples of circular motion (vehicle on a level circular road, vehicle on a banked road).

Unit IV: Work, Energy and Power 12 Periods

Work done by a constant force and a variable force; kinetic energy, work-energy theorem, power.

Notion of potential energy, potential energy of a spring, conservative forces: conservation of mechanical energy (kinetic and potential energies); non-conservative forces: motion in a vertical circle; elastic and inelastic collisions in one and two dimensions.

Unit V: Motion of System of Particles and Rigid Body 18 Periods

Centre of mass of a two-particle system, momentum conservation and centre of mass motion.

Centre of mass of a rigid body; centre of mass of a uniform rod.

Moment of a force, torque, angular momentum, laws of conservation of angular momentum and its applications.

Equilibrium of rigid bodies, rigid body rotation and equations of rotational motion, comparison of linear and rotational motions.

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Moment of inertia, radius of gyration, values of moments of inertia for simple geometrical objects (no derivation). Statement of parallel and perpendicular axes theorems and their applications.

Unit VI: Gravitation 12 Periods

Kepler's laws of planetary motion, universal law of gravitation.

Acceleration due to gravity and its variation with altitude and depth.

Gravitational potential energy and gravitational potential, escape velocity, orbital velocity of a satellite. Geo-stationary satellites.

Unit VII: Properties of Bulk Matter 24 Periods

Elastic behaviour, Stress-strain relationship, Hooke's law, Young's modulus, bulk modulus, shear modulus of rigidity, Poisson's ratio; elastic energy.

Pressure due to a fluid column; Pascal's law and its applications (hydraulic lift and hydraulic brakes), effect of gravity on fluid pressure.

Viscosity, Stokes' law, terminal velocity, streamline and turbulent flow, critical velocity, Bernoulli's theorem and its applications.

Surface energy and surface tension, angle of contact, excess of pressure across a curved surface, application of surface tension ideas to drops, bubbles and capillary rise.

Heat, temperature, thermal expansion; thermal expansion of solids, liquids and gases, anomalous expansion of water; specific heat capacity; Cp, Cv - calorimetry; change of state - latent heat capacity.

Heat transfer-conduction, convection and radiation, thermal conductivity, qualitative ideas of Blackbody radiation, Wein's displacement Law, Stefan's law, Green house effect.

Unit VIII: Thermodynamics 12 Periods

Thermal equilibrium and definition of temperature (zeroth law of thermodynamics), heat, work and internal energy. First law of thermodynamics, isothermal and adiabatic processes.

Second law of thermodynamics: reversible and irreversible processes, Heat engine and refrigerator.

Unit IX: Behaviour of Perfect Gases and Kinetic Theory of Gases 08 Periods

Equation of state of a perfect gas, work done in compressing a gas.

Kinetic theory of gases - assumptions, concept of pressure. Kinetic interpretation of temperature; rms speed of gas molecules; degrees of freedom, law of equi-partition of energy (statement only) and application to specific heat capacities of gases; concept of mean free path, Avogadro's number.

Unit X: Oscillations and Waves 26 Periods

Periodic motion - time period, frequency, displacement as a function of time, periodic functions.

Simple harmonic motion (S.H.M) and its equation; phase; oscillations of a spring-restoring force and force constant; energy in S.H.M. Kinetic and potential energies; simple pendulum derivation of expression for its time period.

Free, forced and damped oscillations (qualitative ideas only), resonance.

Wave motion: Transverse and longitudinal waves, speed of wave motion, displacement relation for a progressive wave, principle of superposition of waves, reflection of waves, standing waves in strings and organ pipes, fundamental mode and harmonics, Beats, Doppler effect.

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PRACTICALS Total Periods: 60

The record, to be submitted by the students, at the time of their annual examination, has to include:

Record of at least 15 Experiments [with a minimum of 6 from each section], to be performed by the students.

Record of at least 5 Activities [with a minimum of 2 each from section A and section B], to be demonstrated by the teachers.

Report of the project to be carried out by the students.

EVALUATION SCHEME

Two experiments one from each section 8+8 Marks

Practical record (experiment and activities) 6 Marks

Investigatory Project 3 Marks

Viva on experiments, activities and project 5 Marks

Total 30 Marks

SECTION–A Experiments

1. To measure diameter of a small spherical/cylindrical body and to measure internal diameter and depth of a given beaker/calorimeter using Vernier Callipers and hence find its volume.

2. To measure diameter of a given wire and thickness of a given sheet using screw gauge.

3. To determine volume of an irregular lamina using screw gauge.

4. To determine radius of curvature of a given spherical surface by a spherometer.

5. To determine the mass of two different objects using a beam balance.

6. To find the weight of a given body using parallelogram law of vectors.

7. Using a simple pendulum, plot its L-T2 graph and use it to find the effective length of second's pendulum.

8. To study variation of time period of a simple pendulum of a given length by taking bobs of same size but different masses and interpret the result.

9. To study the relationship between force of limiting friction and normal reaction and to find the co-efficient of friction between a block and a horizontal surface.

10. To find the downward force, along an inclined plane, acting on a roller due to gravitational pull of the earth and

study its relationship with the angle of inclination θ by plotting graph between force and sinθ.

Activities (for the purpose of demonstration only)

1. To make a paper scale of given least count, e.g., 0.2cm, 0.5 cm.

2. To determine mass of a given body using a metre scale by principle of moments.

3. To plot a graph for a given set of data, with proper choice of scales and error bars.

4. To measure the force of limiting friction for rolling of a roller on a horizontal plane.

5. To study the variation in range of a projectile with angle of projection.

6. To study the conservation of energy of a ball rolling down on an inclined plane (using a double inclined plane).

7. To study dissipation of energy of a simple pendulum by plotting a graph between square of amplitude and time.

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SECTION–B

Experiments

1. To determine Young's modulus of elasticity of the material of a given wire.

2. To find the force constant of a helical spring by plotting a graph between load and extension.

3. To study the variation in volume with pressure for a sample of air at constant temperature by plotting graphs between P and V, and between P and 1/V.

4. To determine the surface tension of water by capillary rise method.

5. To determine the coefficient of viscosity of a given viscous liquid by measuring terminal velocity of a given spherical body.

6. To study the relationship between the temperature of a hot body and time by plotting a cooling curve.

7. To determine specific heat capacity of a given solid by method of mixtures.

8. To study the relation between frequency and length of a given wire under constant tension using sonometer.

9. To study the relation between the length of a given wire and tension for constant frequency using sonometer.

10. To find the speed of sound in air at room temperature using a resonance tube by two resonance positions.

Activities (for the purpose of demonstration only)

1. To observe change of state and plot a cooling curve for molten wax.

2. To observe and explain the effect of heating on a bi-metallic strip.

3. To note the change in level of liquid in a container on heating and interpret the observations.

4. To study the effect of detergent on surface tension of water by observing capillary rise.

5. To study the factors affecting the rate of loss of heat of a liquid.

6. To study the effect of load on depression of a suitably clamped metre scale loaded at (i) its end (ii) in the middle.

7. To observe the decrease in presure with increase in velocity of a fluid.

Practical Examination for Visually Impaired Students Class XI

Note: Same Evaluation scheme and general guidelines for visually impaired students as given for Class XII may be followed.

A. Items for Identification/Familiarity of the apparatus for assessment in practicals(All experiments)

Spherical ball, Cylindrical objects, vernier calipers, beaker, calorimeter, Screw gauge, wire, Beam balance, spring balance, weight box, gram and milligram weights, forceps, Parallelogram law of vectors apparatus, pulleys and pans

used in the same ‘weights’ used, Bob and string used in a simple pendulum, meter scale, split cork, suspension arrangement, stop clock/stop watch, Helical spring, suspension arrangement used, weights, arrangement used for

measuring extension, Sonometer, Wedges, pan and pulley used in it, ‘weights’ Tuning Fork, Meter scale, Beam balance, Weight box, gram and milligram weights, forceps, Resonance Tube, Tuning Fork, Meter scale, Flask/Beaker used for adding water.

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B. List of Practicals

1. To measure diameter of a small spherical/cylindrical body using verniercalipers.

2. To measure the internal diameter and depth of a given beaker/calorimeter using verniercalipers and hence find its volume.

3. To measure diameter of given wire using screw gauge.

4. To measure thickness of a given sheet using screw gauge.

5. To determine the mass of a given object using a beam balance.

6. To find the weight of given body using the parallelogram law of vectors.

7. Using a simple pendulum plot L-T and L-T2 graphs. Hence find the effective length of second’s pendulum using appropriate length values.

8. To find the force constant of given helical spring by plotting a graph between load and extension.

9. (i) To study the relation between frequency and length of a given wire under constanttension using a sonometer.

(ii) To study the relation between the length of a given wire and tension, for constantfrequency, using a sonometer.

10. To find the speed of sound in air, at room temperature, using a resonance tube, by observing the two resonance positions.

Note: The above practicals may be carried out in an experiential manner rather than recording observations.

Prescribed Books:

1. Physics Part-I, Textbook for Class XI, Published by NCERT

2. Physics Part-II, Textbook for Class XI, Published by NCERT

3. The list of other related books and manuals brought out by NCERT (consider multimedia also).

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PHYSICS (Code No. 042) QUESTION PAPER DESIGN

CLASS - XI (2014-15)

Time 3 Hours Max. Marks: 70

S. No.

Typology of Questions Very Short Answer (VSA)

(1 mark)

Short Answer-I

(SA-I) (2 marks)

Short Answer –II (SA-II) (3

marks)

Value based question (4 marks)

Long Answer

(LA) (5 marks)

Total Marks

% Weightage

1. Remembering- (Knowledge based Simple recall questions, to know specific facts, terms, concepts, principles, or theories, dentify, define, or recite, information)

2 1 1 – – 7 10%

2 Understanding-(Comprehension -to be familiar with meaning and to understand conceptually, interpret, compare, contrast, explain, paraphrase information)

– 2 4 – 1 21 30%

3 Application (Use abstract - information in concrete situation, to apply knowledge to new situations, Use given content to interpret a situation, provide an example, or solve a problem)

– 2 4 – 1 21 30%

4 High Order Thinking Skills (Analysis & Synthesis- Classify, compare, contrast, or differentiate between different pieces of

2 – 1 – 1 10 14%

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information, Organize and/or integrate unique pieces of information from a variety of sources)

5 Evaluation and Multi-Disciplinary- (Appraise, judge, and/or justify the value or worth of a decision or outcome, or to predict outcomes based on values)

1 – 2 1 – 11 16%

TOTAL 5x1=5 5x2=10 12x3=36 1x4=4 3x5=15 70(26) 100%

QUESTION WISE BREAK UP

Type of Question Mark per Question Total No. of Questions Total Marks

VSA 1 5 05

SA-I 2 5 10

SA-II 3 12 36

VBQ 4 1 04

LA 5 3 15

Total 26 70

1. Internal Choice: There is no overall choice in the paper. However, there is an internal choice in one question of 2 marks weightage, one question of 3 marks weightage and all the three questions of 5 marks weightage.

2. The above template is only a sample. Suitable internal variations may be made for generating similar templates keeping the overall weightage to different form of questions and typology of questions same.

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CLASS XII (2014-15) (THEORY)

One Paper Time: 3 hrs. Max Marks: 70

No. of Periods Marks

Unit I Electrostatics 22 15

Unit II Current Electricity 20

Unit III Magnetic Effect of Current and Magnetism 22 16

Unit IV Electromagnetic Induction and Alternating Current 20

Unit V Electromagnetic Waves 04 17

Unit VI Optics 25

Unit VII Dual Nature of Matter 08 10

Unit VIII Atoms and Nuclei 14

Unit IX Electronic Devices 15 12

Unit X Communication Systems 10

Total 160 70

Unit I: Electrostatics 22 Periods

Electric Charges; Conservation of charge, Coulomb's law-force between two point charges, forces between multiple charges; superposition principle and continuous charge distribution.

Electric field, electric field due to a point charge, electric field lines, electric dipole, electric field due to a dipole, torque on a dipole in uniform electric fleld.

Electric flux, statement of Gauss's theorem and its applications to find field due to infinitely long straight wire, uniformly charged infinite plane sheet and uniformly charged thin spherical shell (field inside and outside).

Electric potential, potential difference, electric potential due to a point charge, a dipole and system of charges; equipotential surfaces, electrical potential energy of a system of two point charges and of electric dipole in an electrostatic field.

Conductors and insulators, free charges and bound charges inside a conductor. Dielectrics and electric polarisation, capacitors and capacitance, combination of capacitors in series and in parallel, capacitance of a parallel plate capacitor with and without dielectric medium between the plates, energy stored in a capacitor.

Unit II: Current Electricity 20 Periods

Electric current, flow of electric charges in a metallic conductor, drift velocity, mobility and their relation with electric current; Ohm's law, electrical resistance, V-I characteristics (linear and non-linear), electrical energy and power, electrical resistivity and conductivity, Carbon resistors, colour code for carbon resistors; series and parallel combinations of resistors; temperature dependence of resistance.

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Internal resistance of a cell, potential difference and emf of a cell, combination of cells in series and in parallel, Kirchhoff's laws and simple applications, Wheatstone bridge, metre bridge.

Potentiometer - principle and its applications to measure potential difference and for comparing EMF of two cells; measurement of internal resistance of a cell.

Unit III: Magnetic Effects of Current and Magnetism 22 Periods

Concept of magnetic field, Oersted's experiment.

Biot - Savart law and its application to current carrying circular loop.

Ampere's law and its applications to infinitely long straight wire. Straight and toroidal solenoids, force on a moving charge in uniform magnetic and electric fields, Cyclotron.

Force on a current-carrying conductor in a uniform magnetic field, force between two parallel current-carrying conductors-definition of ampere, torque experienced by a current loop in uniform magnetic field; moving coil galvanometer-its current sensitivity and conversion to ammeter and voltmeter.

Current loop as a magnetic dipole and its magnetic dipole moment, magnetic dipole moment of a revolving electron, magnetic field intensity due to a magnetic dipole (bar magnet) along its axis and perpendicular to its axis, torque on a magnetic dipole (bar magnet) in a uniform magnetic field; bar magnet as an equivalent solenoid, magnetic field lines; earth's magnetic field and magnetic elements.

Para-, dia- and ferro - magnetic substances, with examples. Electromagnets and factors affecting their strengths, permanent magnets.

Unit IV: Electromagnetic Induction and Alternating Currents 20 Periods

Electromagnetic induction; Faraday's laws, induced EMF and current; Lenz's Law, Eddy currents.

Self and mutual induction.

Alternating currents, peak and RMS value of alternating current/voltage; reactance and impedance; LC oscillations (qualitative treatment only), LCR series circuit, resonance; power in AC circuits, wattless current.

AC generator and transformer.

Unit V: Electromagnetic waves 04 Periods

Need for displacement current, Electromagnetic waves, their characteristics, their Transverse nature (qualitative ideas only).

Electromagnetic spectrum (radio waves, microwaves, infrared, visible, ultraviolet, X-rays, gamma rays) including elementary facts about their uses.

Unit VI: Optics 25 Periods

Ray Optics: Reflection of light, spherical mirrors, mirror formula, refraction of light, total internal reflection and its applications, optical fibres, refraction at spherical surfaces, lenses, thin lens formula, lensmaker's formula, magnification, power of a lens, combination of thin lenses in contact, combination of a lens and a mirror, refraction and dispersion of light through a prism.

Scattering of light - blue colour of sky and reddish apprearance of the sun at sunrise and sunset.

Optical instruments: Microscopes and astronomical telescopes (reflecting and refracting) and their magnifying powers.

10

Wave optics: Wave front and Huygen's principle, reflection and refraction of plane wave at a plane surface using wave fronts. Proof of laws of reflection and refraction using Huygen's principle. Interference, Young's double slit experiment and expression for fringe width, coherent sources and sustained interference of light, diffraction due to a single slit, width of central maximum, resolving power of microscope and astronomical telescope, polarisation, plane polarised light, Brewster's law, uses of plane polarised light and Polaroids.

Unit VII: Dual Nature of Matter and Radiation 08 Periods

Dual nature of radiation, Photoelectric effect, Hertz and Lenard's observations; Einstein's photoelectric equation-particle nature of light.

Matter waves-wave nature of particles, de-Broglie relation, Davisson-Germer experiment (experimental details should be omitted; only conclusion should be explained).

Unit VIII: Atoms and Nuclei 14 Periods

Alpha-particle scattering experiment; Rutherford's model of atom; Bohr model, energy levels, hydrogen spectrum.

Composition and size of nucleus, Radioactivity, alpha, beta and gamma particles/rays and their properties; radioactive decay law.

Mass-energy relation, mass defect; binding energy per nucleon and its variation with mass number; nuclear fission, nuclear fusion.

Unit IX: Electronic Devices 15 Periods

Energy bands in conductors, semiconductors and insulators (qualitative ideas only)

Semiconductor diode - I-V characteristics in forward and reverse bias, diode as a rectifier;

Special purpose p-n junction diodes: LED, photodiode, solar cell and Zener diode and their characteristics, zener diode as a voltage regulator.

Junction transistor, transistor action, characteristics of a transistor, transistor as an amplifier (common emitter configuration), basic idea of analog and digital singals, Logic gates (OR, AND, NOT, NAND and NOR).

Unit X: Communication Systems 10 Periods

Elements of a communication system (block diagram only); bandwidth of signals (speech, TV and digital data); bandwidth of transmission medium. Propagation of electromagnetic waves in the atmosphere, sky and space wave propagation, satellite communication. Need for modulation, amplitude modulation and frequency modulation, advantages of frequency modulation over amplitude modulation. Basic ideas about internet, mobile telephony and global positioning system (GPS)

PRACTICALS (Total Periods 60)

The record to be submitted by the students at the time of their annual examination has to include:

Record of at least 15 Experiments [with a minimum of 6 from each section], to be performed by the students.

Record of at least 5 Activities [with a minimum of 2 each from section A and section B], to be demonstrated by the teachers.

The Report of the project to be carried out by the students.

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Evaluation Scheme

Two experiments one from each section 8+8 Marks

Practical record [experiments and activities] 6 Marks

Investigatory Project 3 Marks

Viva on experiments, activities and project 5 Marks

Total 30 marks

SECTION–A

Experiments

1. To determine resistance per cm of a given wire by plotting a graph for potential difference versus current.

2. To find resistance of a given wire using metre bridge and hence determine the resistivity (specific resistance) of its material

3. To verify the laws of combination (series) of resistances using a metre bridge.

4. To verify the laws of combination (parallel) of resistances using a metre bridge.

5. To compare the EMF of two given primary cells using potentiometer.

6. To determine the internal resistance of given primary cell using potentiometer.

7. To determine resistance of a galvanometer by half-deflection method and to find its figure of merit.

8. To convert the given galvanometer (of known resistance and figure of merit) into a voltmeter of desired range and to verify the same.

9. To convert the given galvanometer (of known resistance and figure of merit) into an ammeter of desired range and to verify the same.

10. To find the frequency of AC mains with a sonometer.

Activities (For the purpose of demonstration only)

1. To measure the resistance and impedance of an inductor with or without iron core.

2. To measure resistance, voltage (AC/DC), current (AC) and check continuity of a given circuit using multimeter.

3. To assemble a household circuit comprising three bulbs, three (on/off) switches, a fuse and a power source.

4. To assemble the components of a given electrical circuit.

5. To study the variation in potential drop with length of a wire for a steady current.

6. To draw the diagram of a given open circuit comprising at least a battery, resistor/rheostat, key, ammeter and voltmeter. Mark the components that are not connected in proper order and correct the circuit and also the circuit diagram.

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SECTION–B

Experiments

1. To find the value of v for different values of u in case of a concave mirror and to find the focal length.

2. To find the focal length of a convex mirror, using a convex lens.

3. To find the focal length of a convex lens by plotting graphs between u and v or between 1/u and 1/v.

4. To find the focal length of a concave lens, using a convex lens.

5. To determine angle of minimum deviation for a given prism by plotting a graph between angle of incidence and angle of deviation.

6. To determine refractive index of a glass slab using a travelling microscope.

7. To find refractive index of a liquid by using convex lens and plane mirror.

8. To draw the I-V characteristic curve for a p-n junction in forward bias and reverse bias.

9. To draw the characteristic curve of a zener diode and to determine its reverse break down voltage.

10. To study the characteristic of a common - emitter npn or pnp transistor and to find out the values of current and voltage gains.

Activities (For the purpose of demonstration only)

1. To identify a diode, an LED, a transistor, an IC, a resistor and a capacitor from a mixed collection of such items.

2. Use of multimeter to (i) identify base of transistor, (ii) distinguish between npn and pnp type transistors, (iii) see the unidirectional flow of current in case of a diode and an LED, (iv) check whether a given electronic component (e.g., diode, transistor or IC) is in working order.

3. To study effect of intensity of light (by varying distance of the source) on an LDR.

4. To observe refraction and lateral deviation of a beam of light incident obliquely on a glass slab.

5. To observe polarization of light using two Polaroids.

6. To observe diffraction of light due to a thin slit.

7. To study the nature and size of the image formed by a (i) convex lens, (ii) concave mirror, on a screen by using a candle and a screen (for different distances of the candle from the lens/mirror).

8. To obtain a lens combination with the specified focal length by using two lenses from the given set of lenses.

Suggested Investigatory Projects

1. To study various factors on which the internal resistance/EMF of a cell depends.

2. To study the variations in current flowing in a circuit containing an LDR because of a variation in

(a) the power of the incandescent lamp, used to 'illuminate' the LDR (keeping all the lamps at a fixed distance). (b) the distance of a incandescent lamp (of fixed power) used to 'illuminate' the LDR.

3. To find the refractive indices of (a) water (b) oil (transparent) using a plane mirror, an equi convex lens (made from a glass of known refractive index) and an adjustable object needle.

4. To design an appropriate logic gate combination for a given truth table.

5. To investigate the relation between the ratio of (i) output and input voltage and (ii) number of turns in the secondary coil and primary coil of a self designed transformer.

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6. To investigate the dependence of the angle of deviation on the angle of incidence using a hollow prism filled one by one, with different transparent fluids.

7. To estimate the charge induced on each one of the two identical styrofoam (or pith) balls suspended in a vertical plane by making use of Coulomb's law.

8. To set up a common base transistor circuit and to study its input and output characteristic and to calculate its current gain.

9. To study the factor on which the self inductance of a coil depends by observing the effect of this coil, when put in series with a resistor/(bulb) in a circuit fed up by an A.C. source of adjustable frequency.

10. To construct a switch using a transistor and to draw the graph between the input and output voltage and mark the cut-off, saturation and active regions.

11. To study the earth's magnatic field using a tangent galvanometer.

Practical Examination for Visually Impaired Students of Classes XI and XII Evaluation Scheme

Time Allowed: Two hours Max. Marks: 30

Identification/Familiarity with the apparatus 5 marks

Written test (based on given/prescribed practicals) 10 marks

Practical Record 5 marks

Viva 10 marks

Total 30 marks

General Guidelines

The practical examination will be of two hour duration.

A separate list of ten experiments is included here.

The written examination in practicals for these students will be conducted at the time of practical examination of all other students.

The written test will be of 30 minutes duration.

The question paper given to the students should be legibly typed. It should contain a total of 15 practical skill based very short answer type questions. A student would be required to answer any 10 questions.

A writer may be allowed to such students as per CBSE examination rules.

All questions included in the question papers should be related to the listed practicals. Every question should require about two minutes to be answered.

These students are also required to maintain a practical file. A student is expected to record at least five of the listed experiments as per the specific instructions for each subject. These practicals should be duly checked and signed by the internal examiner.

The format of writing any experiment in the practical file should include aim, apparatus required, simple theory, procedure, related practical skills, precautions etc.

Questions may be generated jointly by the external/internal examiners and used for assessment.

The viva questions may include questions based on basic theory/principle/concept, apparatus/materials/chemicals required, procedure, precautions, sources of error etc.

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Class XII

A. Items for Identification/ familiarity with the apparatus for assessment in practicals(All experiments)

Meter scale, general shape of the voltmeter/ammeter, battery/power supply, connecting wires, standard resistances, connecting wires, voltmeter/ammeter, meter bridge, screw gauge, jockey Galvanometer, Resistance Box, standard Resistance, connecting wires, Potentiometer, jockey, Galvanometer, Lechlanche cell, Daniell cell

(simple distinction between the two vis-à-vis their outer (glass and copper) containers, rheostat connecting wires, Galvanometer, resistance box, Plug-in and tapping keys, connecting wires battery/power supply, Diode, Transistor, IC, Resistor (Wire-wound or carbon ones with two wires connected to two ends), capacitors (one or two types), Inductors, Simple electric/electronic bell, battery/power supply, Plug-in and tapping keys, Convex lens, concave lens, convex mirror, concave mirror, Core/hollow wooden cylinder, insulated wire, ferromagnetic rod, Transformer core, insulated wire.

B. List of Practicals

1. To determine the resistance per cm of a given wire by plotting a graph between voltage and current.

2. To verify the laws of combination (series/parallel combination) of resistances by ohm’s law.

3. To find the resistance of a given wire using a meter bridge and hence determine the specific resistance (resistivity) of its material.

4. To compare the e.m.f of two given primary cells using a potentiometer.

5. To determine the resistance of a galvanometer by half deflection method.

6. To identify a

(i) diode, transistor and IC

(ii) resistor, capacitor and inductor, from a mixed collection of such items.

7. To understand the principle of (i) a NOT gate (ii) an OR gate (iii)an AND gate and to make their equivalent circuits using a bell and cells/battery and keys /switches.

8. To observe the difference between

(i) a convex lens and a concave lens

(ii) a convex mirror and a concave mirror and to estimate the likely difference between the power of two given convex /concave lenses.

9. To design an inductor coil and to know the effect of

(i) change in the number of turns

(ii) introduction of ferromagnetic material as its core material on the inductance of the coil.

10. To design a (i) step up (ii) step down transformer on a given core and know the relation between its input and output voltages.

Note: The above practicals may be carried out in an experiential manner rather than recording observations.

Prescribed Books:

1. Physics, Class XI, Part -I and II, Published by NCERT.

2. Physics, Class XII, Part -I and II, Published by NCERT.

3. The list of other related books and manuals brought out by NCERT (consider multimedia also).

15

PHYSICS (Code No. 042) QUESTION PAPER DESIGN

CLASS - XII (2014-15)

Time 3 Hours Max. Marks: 70

S. No.

Typology of Questions

Very Short Answer (VSA)

(1 mark)

Short Answer-I

(SA-I) (2 marks)

Short Answer –II (SA-II) (3

marks)

Value based question (4 marks)

Long Answer

(LA) (5 marks)

Total Marks

% Weightage

1. Remembering- (Knowledge based Simple recall questions, to know specific facts, terms, concepts, principles, or theories, Identify, define, or recite, information)

2 1 1 – – 7 10%

2 Understanding- (Comprehension -to be familiar with meaning and to understand conceptually, interpret, compare, contrast, explain, paraphrase information)

– 2 4 – 1 21 30%

3 Application (Use abstract information in concrete situation, to apply knowledge to new situations, Use given content to interpret a situation, provide an example, or solve a problem)

– 2 4 – 1 21 30%

4 High Order Thinking Skills (Analysis & Synthesis- Classify, compare, contrast, or differentiate between different pieces of

2 – 1 – 1 10 14%

16

information, Organize and/or integrate unique pieces of information from a variety of sources)

5 Evaluation and Multi-Disciplinary- (Appraise, judge, and/or justify the value or worth of a decision or outcome, or to predict outcomes based on values)

1 – 2 1 – 11 16%

TOTAL 5x1=5 5x2=10 12x3=36 1x4=4 3x5=15 70(26) 100%

QUESTION WISE BREAK UP

Type of Question Mark per Question Total No. of Questions Total Marks

VSA 1 5 05

SA-I 2 5 10

SA-II 3 12 36

VBQ 4 1 04

LA 5 3 15

Total 26 70

1. Internal Choice: There is no overall choice in the paper. However, there is an internal choice in one question of 2 marks weightage, one question of 3 marks weightage and all the three questions of 5 marks weightage.

2. The above template is only a sample. Suitable internal variations may be made for generating similar templates keeping the overall weightage to different form of questions and typology of questions same.

17

pankaj

Text Box

Source:- 1. http:// www.cbse.nic.in 2. Delhi State Science Teachers Forum

18

Changes in Physics Syllabus for March 2015, Examination

Class XI

Theory

1. Weightage assigned to an individual unithas been removed. However, collective weightage to group of units has been assigned.

2. From Unit VII (Properties of Bulk Matter) topics named ‘Reynold’s number’ and ‘Newton’s law of cooling’ have been deleted.

Practicals

3. At the time of annual examination, students have to submit a report of the project carried out by them instead of at least two demonstration experiments.

4. In Evaluation Scheme, a weightage of 3 marks has been assigned to this investigatory project and a weightage of 5 marks has been assigned to viva on experiments, activities and project, keeping the rest as same. (For detail, one may refer to 2015 curriculum on Board’s website).

5. Total number of experiments given in Section A has been reduced from 11 to 10 by merging the experiment number 1 and 2 into one and 3 and 4 as one,along with the addition of a new experiment at number 8 aiming “To study variation of time period of a simple pendulum of a given length by taking bobs of same size but different masses and interpret the result”.

6. The number of available experiments in section B has been increased by proving an optional choice among part (i) and (ii) of experiment number 8.

Class XII

Theory

1. Weightage assigned to an individual unit in terms of marks has been removed. However, collective weightage to group of units has been assigned.

2. From Unit I (Electrostatics) topic named ‘Van de Graaff generator’ has been deleted.

3. From Unit VI (Optics) topics named ‘Human eye, image formation and accommodation, correction of eye defect (myopia, hypermetropia) using lenses’ have been deleted.

4. From Unit VIII (Atoms and Nuclei) topics named ‘atomic masses, isotopes, isobars, and isotones’ have been deleted.

19

5. From Unit IX (Electronic Devices) topics named ‘Oscillator’ and ‘Transistor as a switch’ have been deleted.

6. In unit X (Communication Systems), topics on ‘Basic ideas about internet, mobile telephony and Global positioning system (GPS)’ have been included.

Practicals

7. The minimum number of activities to be done by the students during the year have been changed from 6 to 5 with a minimum of 2 from each section instead of 3.

pankaj

Text Box


Delhi State Science Teachers Forum

20

DELHI STATE SCIENCE TEACHERS

FORUM


21

List of Experts who contributed in this analysis under the aegis of DSSTF

1. Mr P.C.Bose Retd. D. D of Education

2. Mr. P.N. Varshney Retd. Principal and President DSSTF

3. Dr. R.A. Goyal Retd Principal

4. Mr. Kanhiya Lal Retd Principal

5. Mr. A.P.Agarwal Retd Principal

6. Mr. N.C.Jain Retd. PGT Physics

7. Mr. R.Rangarajan PGT Physics, DTEA School, Lodhi Road.

8. Mr. M.S.Bhandari PGT Physics, Happy School.

9. Mr. R.K.Tiwari H.M. D.A.V. Daryaganj.

10. Mrs. Girija Shankar PGT Physics, Pratibha Vikas Vidyalaya

11. Mrs. Vandana Gupta H.M. D.A.V. Darya Ganj

12. Mrs. Sujatha Jaggi SBV, Ramesh Nagar

13. Mrs. Indra Saini PGT Physics, Ramjas School, Pusa Road.

14. Mr. Ashok Chawla PGT Physics, Ram Mandir School

15. Mrs. Sundari PGT Physics, Andhra School, Prasad Nagar

16. Mr. Brijesh Kumar PGT Physics, Takshila Public School

17. Mrs. Archana Joshi PGT Physics, S.K.V, Rajouri Garden

18. Mrs. Jyoti Singh PGT Physics, Lady Irwin Sr. Sec School

19. Mr. Johnson David DSSTF Treasurer


22

Question-wise analysis of CBSE Question Paper – 2014

CLASS- XII SUBJECT – PHYSICS Code No. 55/1/1 Q.No

Unit Form of Question

Difficult Level E/AV/D/H

Learning Outcome

Quality Of Question Transl-ation

Remark

1. Current Electricity Very Short Average Knowledge Precise 2. Communication

systems Very Short Easy Understanding Precise

3. Current Electricity Very Short Average Knowledge Precise 4. Magnetism Very Short Difficult Application Multiple answers are

possible. Explanation needs a higher award than 1 mark.

For 1 mark the question is very tricky, confusing and bigger.

5. Current Electricity Very Short Easy Understanding Precise 6. Ray Optics Very Short Average Application Precise 7. Magnetic effects Very Short Easy Knowledge Symbol for Charge is

not given. Force should be asked “on” the charge and not “due” to moving charge

Language disturbs the student.

8. Communication Very Short Easy Knowledge Precise 9. Magnetism and

Matter Short Answer

Average Application Precise

10. Electrostatics Short Answer


11. Wave Optics Short Answer

Difficult Application Not Precise about what is expected. The student may not be able to give reason based on path difference. They will explain the whole of the experiment studied.

It is strongly recommended that all students are to be awarded complete 2 marks.

12. Semi-Conductors Short Answer

Easy Understanding Precise.

13. Current Electricity Short Answer

Average Knowledge The word justified is not appropriate.

Any convincingly correct statement of the rules should fetch the


23

complete 2 marks.

14. Alternating current Short Answer

Average Understanding Precise Mark should be given even if the relations are not given.

15. Magnetic Effects of current

Short Answer

Average Knowledge The word “briefly” may not fit better. Demands lengthy answer and 2 marks may not be justifiable. It is a 3 mark question.



17. Dual Nature of matter

Short Answer


18. EMW Short Answer

Average Understanding Precise Good question.

19. Atom and Nulei Short Answer -II

Difficult Application Precise but expects many steps and calculation.

Answer may be given in Terms of Rydbergs constant Or from the difference in energy of the levels

20. EMW Short Answer -II

Easy Application A physics question as a part should have been avoided when value is to be tested. Every part should involve value based questions. The subsections should have been listed as a, b and c rather than with numbers.

21. Current Electricity Short Answer -II

Average Understanding Precise.

22. Ray Optics Short Answer -II

Difficult Application Precise. Too long for a 3 marks. It should be a 5 mark question.

It is suggested that the diagram should be given higher weightage of 2 marks and 1 mark alone be awarded for the numerical part.


24

23. Ray Optics Short Answer -II

Easy Knowledge Precise. - Good question

24. Electrostatics Short Answer -II

Easy Knowledge And Skill

Precise - Good Question.

25. Magnetic Effects of current

Short Answer -II

Average Knowledge and Understanding

Precise. In the second part, it is hard to find the magnetic field outside the system of the solenoids, without having some assumptions like that of Ideal solenoid of length very much greater than their size. The direction identification is difficult as the inequality of n1 and n2 is not defined.

- Complexity should have been avoided. It is strongly recommended that the distribution of marks may be 1and 1 for the first two parts and 1 mark should be awarded for the 3rd part to every student since it is not precisely in the course.


Average Knowledge Precise. Expects memorizing the value of frequencies of components of EM spectrum. The magnitude of physical quantities may be asked in terms of order of magnitude.

Mark for I part should be awarded for every student who names the wave.

27. Atom and Nuclei Short Answer -II

Average Knowledge and Understanding

Precise. It is suggested that the mark distribution may be 2, ½ and ½ for the three subsects.

28. Wave Optics Long Answer Type

Average Understanding and Application

Precise.

29. Electro magnetic Induction

Long Answer Type

Difficult Knowledge & Application

Precise. The growth of current should have been given to be at constant rate. The language of the “OR” part brings confusion as time is not mentioned with magnetic flux.

Good Question. One mark should be awarded for the I part of section(a) Marks are to be awarded for all students in the part(b) of the “OR” part.

30. Semi-Conductors Long Answer Type

Average Knowledge & Application

Precise. Good Question.


25


[Only Uncommon Questions]

CLASS- XII SUBJECT – PHYSICS Code No. 55/1/2 Q.No



Learning Outcome

Quality OF Question

Translation

Remark



3. Current Electricity Very Short Easy Understanding Precise 10. Electrostatics Short

Answer Average Application Precise


Short Answer




20. Atom and Nulei Short Answer -II

Difficult Application Precise but expects many steps and calculation.





26


[Only Uncommon Questions]

CLASS- XII SUBJECT – PHYSICS Code No. 55/1/3 Q.No.



Learning Outcome

Quality OF Question

Translation

Remark



4. Current Electricity Very Short Easy Understanding Precise 9. Electrostatics Short

Answer Average Application Precise


Short Answer








27

Unit Wise Distribution of Marks

Unit Name of the Unit Marks allotted Marks in the paper

I Electrostatics 08 07

II Current Electricity 07 08

III Magnetic effect of current & Magnetism 08 09

IV Electromagnetic Induction and Alternating current 08 07

V Electromagnetic Waves 03 03

VI Optics 14 14

VII Dual Nature of Matter 04 04

VIII Atoms and Nuclei 06 06

IX Electronic Devices 07 07

X Communication Systems 05 05

Total 70 70


28

Difficulty Level Wise Distribution of Marks

S.No. Estimated difficulty level Marks

1. Easy 21% [15/70]

2. Average 59% [41/70]

3. Difficult 20% [14/70] *There is a shift of 5% from the Average to Easy category. *Estimated difficulty level percentage is closely matching with the design of the

question paper. *Weight-age of numerical problems is closely matching with the design of the question

paper.

pankaj

Text Box


Delhi State Science Teachers’ Forum

1. Define the term ‘Mobility’ of charge carriers in a conductor. Write its S.I. unit.Sol. Velocity per unit electric field with the charges is called as Mobility or [1/2]

S.I. unit = –1 C m s–1 or m2 V-1 s-1 [1/2]2. The carrier wave is represented by

C(t) = 2 sin (8 t) voltA modulating signal is a square wave as shown. Determine modulation index.

m(t)

1

1 t(s)

Sol. Am= 1, Ac = 2, [1/2]

c

m

A

A = 1/2 = 0.5 [1/2]

3. “For any charge configuration, equipotential surface through a point is normal to the electricfield.” Justify.

Sol. If the field were not normal to the equipotential surface, it would have non-zero component alongthe surface. This field may move the charge along the surface without any energy supply violatingthe law of conservation of energy. [1]

4. Two spherical bobs, one metallic and the other of glass, of the same size are allowed to fall freelyfrom the same height above the ground. Which of the two would reach earlier and why ?

Sol. Due to motion, in metallic bob, eddy current will be produced which will oppose the motion andslows the metallic bob. It will take more time in reaching the ground. So, the glass bob will reachthe ground earlier. [1]

5. Show variation of resistivity of Copper as a function of temperature in a graph.

Sol.

T [1]

6. A convex lens is placed in contact with a plane mirror. A point object at a distance of 20 cm onthe axis of this combination has its image coinciding with itself. What is the focal length of thelens?

Sol. Since image coincides with object, it implies that ray must befalling normally on the plane mirror. This implies that the rayafter passing through lens becomes parallel. So, object mustbe at the focus of lens.

So, focal length of lens = 20 cm. [1]

7. Write the expression, in a vector form, for the Lorentz magnetic force F due to a charge moving

with velocity v in a magnetic field B . What is the direction of the magnetic force ?

E

vd

O

20 cm

55/1/1

29

Delhi State Science Teachers’ ForumSol. F q v B [1/2]

The direction of magnetic force must be perpendicular to the plane containing v and B and isgiven by Fleming’s left hand rule. [1/2]

8. The figure given below shows the block diagram of a generalized communication system. Identifythe element labelled ‘X’ and write its function.

MessageSignal

MessageSignal

User

InformationSource

X

Transmitter Receiver

Sol. X Channel [1/2]Channel: Medium through which signal travels. The channel is open space in case of radio or TVtransmission. [1/2]

9. Out of the two magnetic materials, ‘A’ has relative permeability slightly greater than unity while‘B’ has less than unity. Identify the nature of the materials ‘A’ and ‘B’ Will their susceptibilitiesbe positive or negative.

Sol. Material A is paramagnetic. Material B is diamagnetic. [4 * 1/2]Susceptibility of A is positive and susceptibility of B is negative.

10. Given a uniform electric field E = 5 x 103 i N/C, find the flux of this field through a square ofside 10 cm, whose plane is parallel to the y–z plane. What would be the flux through the samesquare, if the plane makes an angle of 30° with the x-axis?

Sol. When plane of square in parallel to YZ-plane, flux of electric field

1 E . A as area vector is parallel along x-axis [1/2]

Vmxxx 50)101010).(105( 43

1 = 50 V-m [1/2]When plane make 30° with x-axis

2 = EA cos Vmxxx 2560cos)101010).(105( 43 [1]

11. For a single slit of width “a”, the first minimum of the interference pattern of a monochromatic

light of wavelength occurs at an angle of .a

At the same angle of ,a we get a maximum for

two narrow slits separated by a distance “a”. Explain.Sol. The condition for minima is single slit is

a sin = nFor first minima and for small angle

a =

= aThe minima can be explained by dividing two slits in two equal halves. For every secondarysource in upper slit cancels the corresponding contribution of secondary source in second slit

which differ’s in path length by 2 . [1]

Whereas the condition for maxima in two narrow slits isa sin = n

30


for first maxima and for small angle = a [1]

In this case the path difference between the waves reaching screen is and will be contributingto maximum.

12. Write the truth table for the combination of the gates shown. Name the gates used.

YA

BR

A

YS

Sol. R is OR Gate [1/2+1/2+1]and S in AND GateTruth table :

A B Y = A + B Y = A(A + B)0 0 0 0 0 1 1 0 1 0 1 1 1 1 1 1

OR12. Identify the logic gates marked ‘P’ and ‘Q’ in the given circuit. Write the truth table for the

combination.

X

A

BQP

Sol. P in NAND GateQ is OR Gate [1/2+1/2+1]Truth table :

A B AB B AB 0 0 1 1 0 1 1 1 1 0 1 1 1 1 0 1

13. State Kirchhoff s rules. Explain briefly how these rules are justified.Sol. Kirchoff’s Current (Junction) rule: At any junction, the sum of the currents entering the junction

is equal to the sum of current leaving the junction. [1]When currents are steady, there is no accumulation of charge at any junction or at any point ina line. This is based on the conservation of charge.Kirchoff loop rule: The algebric sum of changes in potential difference across all the elementsin any closed loop involving resistors and cells is zero.This law is based on the conservation of energy. [1]

14. A capacitor ‘C’ a variable resistor ‘R’ and a bulb ‘B’ are connected in series to the ac main; in circuitas shown. The bulb glows with some brightness. How will the glow of the bulb change if (i) a dielectricslab is introduced between the plates of the capacitor, keeping resistance R to be the same; (ii) theresistance R is increased keeping the same capacitance ?

R BC

Mains

31

Delhi State Science Teachers’ ForumSol. (a) When dielectric slab is introduced between the plates of capacitor, its capacitance increases

and reactance decreases. This increases the current flowing in bulb and so the bulb glowsbrighter with resistance unaltered. [1]

(b) When resistance increases, current flowing in circuit decreases. Glow of bulb decreases. [1]15. State the underlying principle of a cyclotron. Write briefly how this machine is used to accelerate

charged particles to high energies.Sol. Cyclotron : It is a device used to accelerate positively charged particles like protons, deutrons,

-particles etc to very high energies.Principle : A charged particle can be accelerated to very high energies with the help of smallervalues of oscillating electric field. A perpendicular magnetic field which throws the chargedparticle into a circular motion, repeatedly brings the charge into the oscillating electric fieldsuch that repeated acceleration can happen. [1]Working :1. Suppose the positive ion enters the gap between the two dees & finds D1 to be negative and

it gets accelerated towards D1.2. As it enters D1 it doesn’t experience any electric field due to shielding effect of the metallic

dee.3. The perpendicular magnetic field throws it into a circular path.4. At the instant the ion comes out of D1, it finds D1 to be +ve & D1 –ve. It now gets accelerated

towards dee D2.5. It now moves faster through D2 describing a larger semicircle than before.6. Thus, the +ve ion will go on accelerating every time it comes into the gap between the dees

and will go on describing circular path of greater and greater radius with greater speed andfinally acquire a sufficiently high energy.

7. The accelerated ion is ejected through a window by a deflecting voltage and hits the target.[1]

16. An electric dipole of length 4 cm, when placed with its axis making an angle of 60° with a

uniform electric field, experiences a torque of 34 Nm. Calculate the potential energy of the

dipole, if it has a charge of ± 8 nC.Sol. Torque = PE sin

Exxxx2

310410834 29

E = 4 × 10-11 V/m [1+1]

Potential energy of dipoleU = –PE cos

U = –8 × 10–9 × 4 × 10–2 × 4 × 10-11 × 12 = –64 J

U = –64 J17. A proton and a deuteron are accelerated through the same potential. Which one of the two has

(i) greater value of de-Broglie wavelength associated with it and (ii) less momentum. Give reasons tojustify your answer.

Sol. V = Accelerating potential [4 *1/2]

60°

E

–q +q

32


(i) Debroglie Wavelength h hmv p

since eVmp 2

eVm

h

eVm

hd 422

)

The de Broglie wavelength for proton is more than debroglie wavelength of duetron.

(ii) Kinetic energy of proton Kp = eV. So momentum pp = meV2

Kinetic energy of deutron K = 2eV. So momentum = pd = eVm4

So, momentum of proton is less than that of the deutron.18. (i) Monochromatic light of frequency 6.0 x 1014 Hz is produced by a laser. The power emitted is

2.0 × 10–3 W. Estimate the number of photons emitted per second on an average by thesource.

(ii) Draw a plot showing the variation of photoelectric current versus the intensity of incidentradiation on a given photosensitive surface.

Sol. (i) We know energy of photon = h

= 6.63 × 10–34 × 6 × 1014 Joule = 6 × 6.63 × 10–20 [1+1]So, No. of photons emitted per second on an average by the source is

= 3 17

20Power 2 10 10

Energy of one photon 19.896.63 6 10 = 5.03 × 1015

(ii) Photocurrent

Intensity

19. A 12.5 eV beam of electrons is used to bombard gaseous hydrogen at room temperature. Uptowhich energy level the hydrogen atoms would be excited ?Calculate the wavelength of the first member of Lyman and first member of Balmer series.

Sol. (i) E = 12.5 eV

Energy in first shell = –13.6 eV [1+1+1]

Energy in nth shell = 2

13.6n

So, drop in energy will be 2

113.6 1 12.9n

13.6 – 12.5 = 213.6n

n2 = 1.1

6.13

n2 = 12.36n = 4 (Maximum 4th level)

33


(ii) For Lyman series, 4

3

4

1

1

11 RR

For Balmer series, n1 = 2, n2 = 3

2 21 1 1 36R

5R2 320. When Sunita, a class XII student, came to know that her parents are planning to rent out the

top floor of their house to a mobile company she protested. She tried hard to convince herparents that this move would be a health hazard.Ultimately her parents agreed:(1) In what way can the setting up of transmission tower by a mobile company in a residential

colony prove to be injurious to health ?(2) By objecting to this move of her parents, what value did Sunita display ?(3) Estimate the range of e.m. waves which can be transmitted by an antenna of height 20 m.

(Given radius of the earth = 6400 km)Sol. (1) Mobile tower requires giant structure at the top level of any building. All through the year

it will be an action point where link will be made with mobiles. In case of large scale wind,there is a fear of fall of the structure. Also, the signals wavering around may affect allhuman life in the neighbourhood. [1+1+1]

(2) By objecting to this move of her parents, Sunita displaced the values that [Any One](i) She is concerned about large scale damage caused by cyclone/high speed wind with

probable loss of life.(ii) She is keeping track (knowledgeable) of the research that is going on in the influence

of these signals on human life when exposed for long duration.(iii) She has foresight of the problems that they may face at large.(iv) She is concerned about the welfare of the community.

(3) Range = R = 3e2 R 2 20 6400 10h

= 64 64 10 = 2 × 8 × 103 = 16 Km

21. A potentiometer wire of length 1.0 m has a resistance of 10 . It is connected to a 6 V battery inseries with a resistance of 5 . Determine the emf of the primary cell which gives a balance pointat 40 cm.

Sol. At balancing point,

Current flowing in the primary circuit is i = A5

2

15

6

510

6 [1] A

5V 5

N B

Potential difference across wire AB

V = volt4105

2

Potential gradient = mVL

V/4

1

4[1]

At balance point = VoltlL

V6.1

100

404

= 1.6 volt [1]

34

Delhi State Science Teachers’ Forum22. (a) Draw a labelled ray diagram showing the formation of a final image by a compound

microscope at least distance of distinct vision.(b) The total magnification produced by a compound microscope is 20. The magnification

produced by the eye piece is 5. The microscope is focussed on a certain object. The distancebetween the objective and eyepiece is observed to be 14 cm. If least distance of distinct visionis 20 cm, calculate the focal length of the objective and the eye piece.

Sol. (a) Compound Microscope : [2+1]

d

u f0

fe

EyepieceB’

h’hA

BB”

ObjectiveA’

E

A”

(b) Magnification produced by eye-piece

D 5ee

mu

20 45eu cm

For eye-piece

1 1 1

e e ev u f

1 1 120 4 ef

1 5 120 ef

20 cm 5cm4ef

Since 50

0

0

00 f

v

u

D

f

vmmm

e

e

5200

0

0

0

f

v

u

D

f

v

e

v0 = 14 – 4 = 10 cm

cmv

f 5.2520

105

200

0

23. (a) A mobile phone lies along the principal axis of a concave mirror. Show, with the help of asuitable diagram, the formation of its image. Explain why magnification is not uniform.(b) Suppose the lower half of the concave mirror’s reflecting surface is covered with an opaque

material. What effect this will have on the image of the object ? Explain.Sol. (a) Image formation of a mobile as an object is shown. Image of one end of the mobile OD is at

the same place while the image of the other end AB is A'B'.The magnification is not uniform along the length and height as, based on the position ofthe portion of the object, magnification is formed. The portion O of the object and the

35

Delhi State Science Teachers’ Forumportion A of the object are separated by a length causing the variation in magnification as

m = vu [2+1]

P A2F

B

O

B

AF

D

(b) We know intensity of image is directly proportional to area of the reflecting surface. Whenhalf part is covered reflecting surface area decreases. So, intensity of image decreases. Butfull image of the object will be formed at the same position as light falls at every point onthe mirror from every point of the object.

24. (a) Obtain the expression for the energy stored per unit volume in a charged parallel platecapacitor.

(b) The electric field inside a parallel plate capacitor is E. Find the amount of work done inmoving a charge q over a closed rectangular loop a b c d a.

a b

cd

+ + ++ ++ ++ ++ + ++

Sol. (a) Assume the capacitor is being charged and, at some moment, has a charge q on it.

The small work needed to transfer a charge dq from one plate to the other: qdW Vdq dqC

The total work required: 2

02

Qq QW dqC C

[2+1]

The energy can be considered to be stored in the electric field between the plates.Energy Density + –

A Bd

ESuppose we have a parallel plate capacitor, as in figure, thefield strength between the plates and total charge are given interms of charge density and plate are A by

0E

Q = ASo, energy stored can be expressed in terms of field strength

212

QUC

2

0

12

dU AA

0ACd

2 2

0

12

dU AA

20

20

12

U dA making 20

1 (Volume between the plates)2

U E

So, energy density, i.e., energy stored per unit volume (uE) is

36


20

1Volume 2E

Uu E

(b) Since, electrostatic field that exists between the positive and negative plate is a conservativefield, the amount of work done in the given path is zero.

OR24. (a) Derive the expression for the capacitance of a parallel plate capacitor having plate area A

and plate separation d.(b) Two charged spherical conductors of radii R1 and R2 when connected by a conducting wire

acquire charges q1 and q2 respectively. Find the ratio of their surface charge densities interms of their radii.

Sol. (a) Let A = surface area of each plate+ –

A Bd

d = Separation between the platesIf is surface charge density of the plates, then electric field

between the plates is given by 0

E

Since, the field is uniform, the potential difference betweenthe plates is

0

dV Ed [2+1]

The total charge on each plate is = ±Q = ± A

Capacitance of a parallel plate capacitor.

QCV

0

Ad making 0AC

d

(b) Since, they are connected, their potentials will be equal with the charges.

Ratio of surface charge densities,

122

21 1 1

22 2 122

4q

4

qRR q

q RR

25. (a) State Ampere’s circuital law, expressing it in the integral form.(b) TWO long coaxial insulated solenoids, S, and S2 of equal lengths are wound one over the

other as shown in the figure. A steady current “I” flow through the inner solenoid S1 to theother end B, which is connected to the outer solenoid S, through which the same current“I” flows in the opposite direction so as to come out at end A. If n1 and n2 are the number ofturns per unit length, find the magnitude and direction of the net magnetic field at a point(i) inside on the axis and (ii) outside the combined system.

l

r1

In1 n2

r2B

S1

S2

A

37


Sol. (a) Integral of magnetic field .B dl around a closed imaginary loop is 0 times current encircled

by the loop.

0. IB dl [1](b) (i) Magnetic field at any point inside the long solenoid is 0nI

Magnetic field due to bigger solenoid = 0n2I towards point ‘B’

Magnetic field due to smaller solenoid = 0n1I towards point ‘A’ [1]So, net magnetic field = 0(n1 – n2)I towards point ‘A’

(ii) Net field due to long solenoid outside is zero, as the fields due to two diametricallyopposite elementary lengths will be zero. [1]

26. Answer the following :(a) Name the em waves which are suitable for radar systems used in aircraft navigation. Write the

range of frequency of these waves.(b) If the earth did not have atmosphere, would its average surface temperature be higher or

lower than what it is now?. Explain.(c) An em wave exerts pressure on the surface on which it is incident. Justify

Sol. (a) MicrowavesFrequency range = 3.0 × 1011 Hz to 1 × 109 Hz [1+1+1]

(b) In the absence of atmosphere, the surface temperature will be less as the higher wavelengthrays reflected from the surface will not be trapped.

(c) For a given em wave of energy E moving with a speed c, momentum transfer is p = EC

happens in a very short time with high velocity. So the momentum transfer of smallermagnitude will exert a force and pressure on any surface .

27. (a) Deduce the expression, N = N0 e– t, for the law of radioactive decay.

(b) (i) Write symbolically the process expressing the + decay of 2211 Na. Also write the basic

nuclear process underlying this decay.

(ii) Is the nucleus formed in the decay of the nucleus 2211 Na , an isotope or isobar ?

Sol. (a) Let N0 = Total number of atoms present originally in a sample at time t = 0N = Total number of atoms left undecayed in the sample at time t [2+1/2+1/2]dN = A small number of atoms that disintegrate in a small interval of time dt

Rate of disintegration of the element

R = dNdt [Minus sign indicates that the number

of atoms left undecayed decreases with time]According to radioactive decay law,

dN Ndt

R = dN Ndt

= Disintegration constant

dN dtN

38


Integrating both side dN dtN

loge N = – t + CC = Constant of integration t = 0N = N0

loge N0 = × 0 + CC = loge N0

loge N = – t + loge N0

loge N – loge N0 = – t

0log N t

N

i.e.,0

tN eN

N = N0 e– t

(b) (i) The basic nuclear process underlying this + decay.p n + e+ +

The reaction is 22 2211 10Na Ne +

(ii) It is an isobar.

28. (a) (i) ‘Two independent monochromatic sources of light cannot produce a sustainedinterference pattern’. Give reason.

(ii) Light waves each of amplitude “a” and frequency “ ”, emanating from two coherentlight sources superpose at a point. If the displacements due to these waves is given byy1 = a cos t and y2 = a cos( t + ) where is the phase difference between the two, obtainthe expression for the resultant intensity at the point.

(b) In Young’s double slit experiment, using monochromatic light of wavelength , the intensityof light at a point on the screen where path difference is , is K units. Find out the intensityof light at a point where path difference is /3.

Sol. (a) (i) In independent monochromatic sources phase difference changes at a rate of 108 Hz.Hence, the interference pattern obtained also fluctuates with 108 Hz and therefore, it isnot sustainable as result of peristance of vision.

(ii) The phase difference between two waves arising from slits A and B is . Then,

y1 = a cos t and y2 = a cos( t + ).

Therefore the resultant displacement will be given by

y = y1 + y2 = a cos t + a cos( t + ) [1+2+2]

y = 2 a cos2

.cos( t +2

)

The amplitude of the resultant displacent is given by

R = 2 a cos (2

)

As, intensity (amplitude)2

Resultant intensity, I = 4a2 cos2(

2)

39


(b) As the resultant intensity at a point, I = I1 + I2 + 1 22 I I cos

When the path difference = , phase difference = 0°

IR= I + I + 2 I I cos 0 = 2I + 22 I 1 = 2I + 2I = 4I = K.

When the path difference = 3 , phase difference 23

I'R = I + I + 22 I.I.cos3

= 2I + 2 12 I2

= 2I – 2I2 = I

I' = K4

OR30. (a) How does one demonstrate, using a suitable diagram, that unpolarised light when passed

through a Polaroid gets polarised ?(b) A beam of unpolarised light is incident on a glass-air interface. Show, using a suitable ray

diagram, that light reflected from the interface is totally polarised, when µ = tan iB, where µis the refractive index of glass with respect to air and iB is the Brewster’s angle.

Sol. (a)

I0 P1

Unpolarised light PolariserPolarised light

I /20

[2+3]

Polariser has a pass axis along which if any electric field vector lies, it will get transmitted tothe other side. If an electric field vector which is perpendicular the pass axis, falls on thepolariser then, it gets absorbed. We know that an unpolarised light has two components ofelectric field vector, one of which is parallel to the pass axis and the other which isperpendicular to the pass axis. Since, the perpendicular component gets absorbed, theoutput light obtained is a polarised light whose electric field vector is parallel to the passaxis.

(b) When unpolarised light is incident on the interface of two transparent media the reflectedlight is polarised. If the unpolarised light is incident at the angles 0° or 90°, the reflected rayremains unpolarised. When the reflected wave is perpendicular to the refracted wave, thereflected wave is totally polarised. The angle of incidence in this case is called polarisingangle or Brewster's angle (ip).

90°

Air

reflected rayincident ray

medium r

iP iP

refracted ray

Brewster's Law says that when an unpolarised light is incident on a transparent surface ofrefractive index (n) at the polarising angle (ip) such that the reflected ray and the refractedray are perpendicular to each other, the reflected light is totally plane polarised and in thatcondition n = tan ip. From the diagram,

ip + 90° + r = 180°

40

Delhi State Science Teachers’ Forumip + r = 90° or r = 90 – ip

sin sin sintan

sin sin(90 ) cosp p p

pp p

i i ii

r i i

29. (a) Describe a simple experiment (or activity) to show that the polarity of emf induced in a coilis always such that it tends to produce a current which opposes the change of magneticflux that produces it.

(b) The current flowing through an inductor of self inductance L is continuously increasing.Plot a graph showing the variation of(i) Magnetic flux versus the current

(ii) Induced emf versus dIdt

(iii) Magnetic potential energy stored versus the current.Sol. (a) As shown in the figure, moving the magnetic closer to the coil increases the flux associated

with the coil. To oppose the rise in magnetic flux, a north pole is developed in the coil, thiscauses as induced current in the anti-clockwise direction as seen from the side of the magnet.

S N

motion

magnetcoil

A B

[2+1+1+1]

(b) (i) Magnetic flux B = LI

B

I

(ii) LdIdt E

dIdt

(iii) 2

0

12Bu B 2

00

1 ( )2

nI

2 20

2Bu n I

2Bu I

OR29. (a) Draw a schematic sketch of an ac generator describing its basic elements. State briefly its

working principle. Show a plot of variation of(i) Magnetic flux and(ii) Alternating emf versus time generated by a loop of wire rotating in a magnetic field.

(b) Why is choke coil needed in the use of fluorescent tubes with ac mains ?Sol. (a) [2+1+1]

I

uB

41

Delhi State Science Teachers’ ForumPrinciple: A dynamo or generator is a device which converts mechanical energy into electricalenergy. It is based on the principle of electromagnetic induction. Magnetic flux changes as thecoils orientation varies with the rotation ( cos cosBA BA t )

Construction: It consists of four main parts-

Field magnet: It produces the magnetic field. For a low power dynamo, the magnetic fieldis generated by a permanent magnet but for a large power dynamo, the magnetic field isproduced by an electromagnet.

N S

B

A

C

D

B1

R1

R2RL

B2

Armature

Fieldmagnet

coil

Slip rings

BrushesLoad resistance

Armature: It consists of a large number of turns of insulated copper wire on a soft ironcore. It can revolve round the axis between the two poles of the field magnet. The soft ironcore provides support to the coils and increases the magnetic field through the coil.

Slip rings: The slip rings R1 and R2 are two metal rings to which the ends of the armaturecoil are connected. These rings are fixed to the shaft which rotates the armature coil so thatthe rings also rotate along with the armature.

Brushes (B1 and B2): These are flexible metal plates or carbon rods which are fixed andconstantly touch the revolving rings. The output current in external load resistance RL istaken through these brushes.(i) B = NBA cos t

2T (Time period)

TB

T/4T/2

3T/4

E

NBA

(ii) E = sind NAB tdt

= E0 sin t making E0 = NAB

E

+E0

–E0

T2

T

42

Delhi State Science Teachers’ Forum(b) Fluorescent tubes have a choke coil which has some inductive reactance, which causes a

delay in the growth of current, thereby reducing the voltage across fluorescent tube. Thisallows the low frequency to pass through. [1]

30. (a) State briefly the processes involved in the formation of p-n junction explaining clearly howthe depletion region is formed.

(b) Using the necessary circuit diagrams, show how the V-I characteristics of a p - n junctionare obtained in (i) Forward biasing (ii) Reverse biasingHow are these characteristics made use of in rectification ? [2+1+1+1]

Sol. (a) Formation of p – n junction: Part of p-type can be converted into n – type by addingpentavalent impurity. There is concentration gradient between p and n sides, holes diffusefrom p side to n side (p n) and electrons move from (n p) creating a layer of positive andnegative charges on n and p side respectively called depletion layer. External bias is appliedto cause charges to flow.

––––

––––

++++

++++

p n

W

metalliccontact depletion

layer

metalliccontact

p-n junction(b) p – n junction under forward bias: When p – side is connected to positive terminal and n –

side to negative terminal of external voltage, it is said to be forward biased. The appliedvoltage V is opposite to built in potential V0, hence depletion layer width decreases andbarrier height is reduced to (V0 – V). There is minority carrier injection, hence charges beginto flow. Current is in the order of mA.

––––

++++

p n

W

V

Forward biased p-n junctionp – n junction under reverse bias: The direction of applied voltage is same as direction ofbarrier potential, so barrier height increases to (V0 + V). This suppresses flow of electronsfrom n p and holes from p n. Diffusion current decreases but drift of electrons andholes under the electric field affect remains. This drift current is few A.

––––––––––––

+ + ++ + ++ + ++ + +

p n

W

Diode under reverse biasStudy of V – I characteristics of a diode: The circuit to study the variation of current as afunction of applied voltage is shown. Battery is connected to potentiometer (or rheostat) tochange applied voltage. In forward bias we use milliammeter and reverse bias we usemicroammeter.

43


+ –switch

(mA) milliammeterp

n

Voltmeter (V)

+–switch

pn

Voltmeter (V)

microammeter ( A)

p-n junction in FB p-n junction in RB

0.2 0.4 0.6 0.8 1.0 V (V)

20406080100

10

20

30

I(mA)

I( A)

Vbr

V

V - I. characteristics graphHalf wave rectifier: Junction diode allows current to pass through only if it is forwardbiased, hence a pulsating voltage will appear across the load only during positive half cycleswhen diode is F.B.

Inputa. c.

Primary

P1

P2

S2

RL

S1

Secondary

A

B

X

Y

transformer

~

time

time

output voltage

Input a. c.

(a) Diode rectification Circuit (b) Input ac and outputvoltage waveforms

OR30. (a) Differentiate between three segments of a transistor on the basis of their size and level of

doping.(b) How is a transistor biased to be in active state ?(c) With the help of necessary circuit diagram, describe briefly how n-p-n transistor in CE

configuration amplifies a small sinusoidal input voltage. Write the expression for the accurrent gain.

Sol. (a) Emitter Base Collector

Doping Highest doping Least doping Moderate Doping

Size Moderate Least Largest

[1+1+3]

(b) Forward bias of input circuit is more than the barrier potential across the input junction.Collector base junction is reverse biased.

(c) Transistor as an amplifier (C E configuration): Transistor works in active region.Output, V0 = VCC – IC RC ...(1)

If input voltage increases, output voltage decreases. Vi and V0 are out of phase.

AV = small signal voltage gain = 0

i

VV

D

D...(2)

44

Delhi State Science Teachers’ ForumSince VCC and RC are constant,

V0 = 0 – RC IC (from (1), differentiate)

IC

IB

RB

ViIE

RC V0

VBBVCC

C

E

C

B

Amplifier CircuitInput Vi = IB RB + VBE

Vi = RB IB + VBE ............(3)

Since VBE = small, neglect it, using (1), (3) in (2),

bR

cR

IR

IRA

bb

ccv where is the current gain.

Voltage gain, bb

cev IR

VA

Uncommon Questions from SET - 2 55/1/2

1. Define the term ‘electrical conductivity’ of a metallic wire. Write its S.I. unit.Sol. Conductivity of a metal is equal to the conductance offered by a wire of unit length and unit

cross-sectional area or 1

[1/2]

S.I. unit = –1 m–1 [1/2]

2. The carrier wave is represented byC(t) = 5 sin (10 t) volt

A modulating signal is a square wave as shown. Determine modulation index.

t in secondm (t) in volt2

1 2

Sol. = M

C

AAmplitude of modulating signal 2 0.4Amplitude of carrier wave A 5 [1]

For just identifying the two values of Am and Ac 1/2 mark may be awarded.3. Show variation of resistivity of Si with temperature in a graph.Sol.

TTemperature dependence of

resistivity for a semiconductor.

[1]

45


10. An electric dipole of length 2 cm, when placed with its axis making an angle of 60° with auniform electric field, experiences a torque of 8 3 Nm. Calculate the potential energy of thedipole, if it has a charge of ± 4 nC.

Sol. Torque = PE sin [1+1]

9 2 38 3 4 10 2 10 (E)2

60°

E

–q +qE = 112

10 = 2 × 1011 V/m

Potential energy of dipoleU = –PE cos

U = –4 × 10–9 × 2 × 10–2 × 2 × 1011 × 12 = –8 J

U = –8 J15. A proton and an alpha particle are accelerated through the same potential. Which one of the two

has (i) greater value of de-Broglie wavelength associated with it and (ii) less kinetic energy. Givereasons to justify your answer.

Sol. V = Accelerating potential


[1+1]

since 2

2p km 2p mk

So,2hmk

2 Vphme

… (i)

2(4 )2 V 16 Vh hm e me … (ii)

8 2 2p

The de Broglie wavelength for proton is more than debroglie wavelength of -particle.(ii) Kinetic energy of proton Kp = eV

Kinetic energy of particle K = 2eVSo, kinetic energy of proton is less than K.E. of -particle.


Sol. When plane of square in parallel to YZ-plane, flux of electric field [1/2]

1 E . A as area vector is parallel along x-axis3 4ˆ ˆ(2 10 ) . (20 20 10 )i i

= 8 × 10

1 = 80 V-m [1/2]When plane make 30° with x-axis

2 = EA cos [1]

46

Delhi State Science Teachers’ Forum= 2 × 103 × 20 × 20 × 10–4 × cos 60°

2 400 1310 410 12

= 40 V-m

20. A 12.9 eV beam of electrons is used to bombard gaseous hydrogen at room temperature. Uptowhich energy level the hydrogen atoms would be excited ?Calculate the wavelength of the first member of Paschen series and first member of Balmerseries.

Sol. (i) E = 12.9 eV [1+1+1]Energy in first shell = –13.6 eV

Energy in nth shell = 2

13.6n

So, drop in energy will be 2

113.6 1 12.9n

13.6 – 12.9 = 213.6n

n2 = 13.60.7

n2 = 19.4n = 4 (Maximum 4th level)

(ii) For Paschen series, 2 21 1 1 16 9R R

16 93 4

= 1447R

For Balmer series, n1 = 2, n2 = 3

2 21 1 1 36R

5R2 322. Answer the following :

(a) Name the em waves which are used for the treatment of certain forms of cancer. Write theirfrequency range.

(b) Thin ozone layer on top of stratosphere is crucial for human survival. Why ?(c) Why is the amount of the momentum transferred by the em waves incident on the surface

so small ?

Sol. (a) -rays [1+1+1]Frequency range = 3.0 × 1018 Hz to 5.0 × 1022 Hz

(b) It prevents the ultraviolet rays coming from sun in reaching the surface of earth. As theseare harmful for human body, the ozone layer is very crucial.

(c) For a given em wave of energy E moving with a speed c, momentum transfer is p = EC

happens in a very short time with high velocity. So, momentum transfer is small.

47

Delhi State Science Teachers’ Forum24. A potentiometer wire of length 1.0 m has a resistance of 15 . It is connected to a 5 V battery in

series with a resistance of 5 . Determine the emf of the primary cell which gives a balance pointat 60 cm.

Sol. At balancing point,

Current flowing in the primary circuit is i = 5 1 A

5 15 4 [1/2]A

5V 5

N BPotential difference across wire AB

V = 1 1515 volt4 4

[1/2]

Potential gradient = V 15 15V/mL 4 1 4

[1]

At balance point = V 15 60 225.L 4 100 100

l [1] = 2.25 volt

Uncommon Questions from SET - 3 55/1/3

1. Define the term ‘drift velocity’ of charge carriers in a conductor and Write its relationship withthe current flowing through it.

Sol. Drift Velocity is defined as the average velocity possessed between successive collisions duringtheir drift in the conductor. [1/2]I= ne Avd. [1/2]

2. The carrier wave is represented byC(t) = 3 sin (8 t) volt

A modulating signal is a square wave as shown. Determine modulation index.

m(t)

1.5

1 2 t(s)

Sol. Am= 1.5 =3/2, Ac = 3, [1/2]

c

m

A

A = 1/2 = 0.5 [1/2]

4. Plot a graph showing variation of current versus voltage for the material GaAS.Sol.

TTemperature dependence of

resistivity for a semiconductor.

48

Delhi State Science Teachers’ Forum9. An electric dipole of length 1 cm, when placed with its axis making an angle of 60° with a

uniform electric field, experiences a torque of 36 Nm. Calculate the potential energy of the

dipole, if it has a charge of ± 2 nC.Sol. Torque = PE sin [1+1]

E = 6 × 1011 V/mPotential energy of dipole

U = –PE cos

U = –2 × 10–9 × 10–2 × 6 × 1011 × 12 = –6 J

U = –6 J12. A deutron and an alpha particle are accelerated through the same potential. Which one of the

two has (i) greater value of de-Broglie wavelength associated with it and (ii) less kinetic energy. Givereasons to justify your answer.

Sol. V = Accelerating potential


[1+1]

since 2

2p km 2p mk

So,2hmk

eVm

hd

)2(2 … (i)

2(4 )2 V 16 Vh hm e me … (ii)

The de Broglie wavelength for deutron is more than debroglie wavelength of -particle. (ii) Kinetic energy of deuton Kd = eV

Kinetic energy of particle K = 2eVSo, kinetic energy of deutron is less than K.E. of -particle.


Sol. When plane of square in parallel to YZ-plane, flux of electric field [1/2]

1 E . A as area vector is parallel along x-axis

)1025104( 43

= 10

1 =10 V-m [1/2]When plane make 30° with x-axis

2 = EA cos [1]= 4 × 103 × 5 × 5 × 10–4 × cos 60°= 10 V-m

E2

31010236 29

60°

E

–q +q

49


22. Answer the following :(a) Name the em waves which are produced during the radioactive decay of a nucleus. Write their

frequency range.(b) Welders wear special goggles while working. Why ? Explain.(c) Why are Infrared waves often called as heat waves? Give their one application.

Sol. (a) -rays [1+1+1]Frequency range = 3.0 × 1018 Hz to 3.0 × 1022 Hz

(b) It prevents the harmful and powerful rays coming from arc reaching the eye. The gogglesfilter the rays.

(c) They produce heat on the surface which are exposed to them. So they are called as Heatwaves. They are said to be received from the Sun. They can be used to dry cloth and invarious electronic tools.

***********

50

pankaj

Text Box


PHYSICS CLASS-XII

SAMPLE PAPER-1

Q1. A magnet is being moved towards a coil with a uniform speed as shown in the

figure. State the direction of the induced current in the resistor R. 1

Q2. A square coil, OPQR, of side a, carrying a current I, is placed in the Y-Z plane as

shown here. Find the magnetic moment associated with this coil. 1

Q3. Give one example each of a ‘system’ that uses the

(i) Sky wave (ii) Space wave

mode of propagation 1

Q4. A concave mirror, of aperture 4cm, has a point object placed on its principal axis

at a distance of 10cm from the mirror. The image, formed by the mirror, is not

likely to be a sharp image. State the likely reason for the same. 1

Q5. Two dipoles, made from charges q and Q, respectively, have equal dipole

moments. Give the (i) ratio between the ‘separations’ of the these two pairs of

charges (ii) angle between the dipole axis of these two dipoles. 1

51

Q6. The graph, shown here, represents the V-I characteristics of a device. Identify the

region, if any, over which this device has a negative resistance. 1

Q7. Define the term ‘Transducer’ for a communication system. 1

Q8. State the steady value of the reading of the ammeter in the circuit shown below.

1

Q9. The following table gives data about the single slit diffraction experiment:

Wave length of Light Half Angular width of

the principal maxima

p q

Find the ratio of the widths of the slits used in the two cases. Would the ratio of

the half angular widths of the first secondary maxima, in the two cases, be also

equal to q? 2

Q10. N spherical droplets, each of radius r, have been charged to have a potential V

each. If all these droplets were to coalesce to form a single large drop, what

would be the potential of this large drop?

(It is given that the capacitance of a sphere of radius r equals 4 kr.)

52

OR

Two point charges, q1 and q2, are located at points (a, o, o) and (o, b, o)

respectively. Find the electric field, due to both these charges, at the point,

(o, o, c). 2

Q11. When a given photosensitive material is irradiated with light of frequency , the

maximum speed of the emitted photoelectrons equals max. The square of max,

i.e., max2, is observed to vary with , as per the graph shown here.

Obtain expressions for

(i) Planck’s constant, and

(ii) The work function of the given photosensitive material,

in terms of the parameters n and the mass, m, of the electron.

Q12. For the circuit shown here, would the balancing length increase, 2

decrease or remain the same, if

(i) R1 is decreased

(ii) R2 is increased

without any other change, (in each case) in the rest of the circuit. Justify your

answers in each case.

53

Q13. Find the P.E. associated with a charge ‘q’ if it were present at the point P with

respect to the ‘set-up’ of two charged spheres, arranged as shown. Here O is the

mid-point of the line O1 O2. 2

Q14. An athlete peddles a stationary tricycle whose pedals are attached to a coil

having 100 turns each of area 0.1m2. The coil, lying in the X-Y plane, is rotated,

in this plane, at the rate of 50 rpm, about the Y-axis, in a region where a

uniform magnetic field, = (0.01) tesla, is present. Find the

(i) maximum emf (ii) average e.m.f

generated in the coil over one complete revolution. 2

Q15. A monochromatic source, emitting light of wave length, 600 nm, has a power

output of 66W. Calculate the number of photons emitted by this source in

2 minutes. 2

Q16. For the circuit shown here, find the

current flowing through the 1 resistor.

Assume

that the two diodes, D1 and D2, are ideal

diodes.

Q17. The following table shows the range of values of susceptibility and relative

magnetic permeability of two different type of magnetic substances

Substance Susceptibility Magnetic Permeability

X -1 to 0 0 to 1

Y >> 1 >> 1

2

54

(a) Identify the type of magnetic materials X and Y.

(b) How does the susceptibility and permeability of X and Y vary with rise in

temperature? 2

Q18. Two wires are aligned parallel to each other. One is carrying an electric current

and the other is not. Will there be any kind of electromagnetic force between

the two? Give reason for your answer. 2

Q19. The galvanometer, in each of the two given circuits, does not show any

deflection. Find the ratio of the resistors R1 and R2, used in these two

circuits. 3

Q20. The electron, in a hydrogen atom, initially in a state of quantum number n1

makes a transition to a state whose excitation energy, with respect to the

ground state, is 10.2 eV. If the wavelength, associated with the photon emitted

in this transition, is 487.5 mm, find the

(i) energy in ev, and (ii) value of the quantum number, n1 of the electron in its

initial state. 3

Q21. Three identical polaroid sheets P1, P2, and P3 are oriented so that the (pass) axis

of P2 and P3 are inclined at angles of 600

and 900, respectively, with respect to

the (pass) axis of P1. A monochromatic

source, S, of intensity I0, is kept in front

of the polaroid sheet P1. Find the

intensity of this light, as observed by

observers O1, O2, and O3, positioned as

shown below.

55

Q22. A fine pencil of -particles, moving with a speed , enters a region (region I),

where a uniform electric and a uniform magnetic field are both present. These

-particles then move into region II where only the magnetic field, (out of the

two fields present in region I), exists. The path of the -particles, in the two

regions, is as shown in the figure.

(i) State the direction of the magnetic field.

(ii) State the relation between ‘E’ and ‘B’ in region I.

(iii) Drive the expression for the radius of the circular path of the -particle in

region II.

If the magnitude of magnetic

field, in region II, is changed

to n times its earlier value,

(without changing the

magnetic field in region I)

find the factor by which the radius of this circular path would change. 3

Q23. Draw an appropriate ray diagram to show the passage of a ‘white ray’, incident

on one of the two refracting faces of a prism. State the relation for the angle of

deviation, for a prism of small refracting angle.

It is known that the refractive index, , of the material of a prism, depends on

the wavelength , , of the incident radiation as per the relation

= A +

where A and B are constants. Plot a graph showing the dependence of on

and identify the pair of variables, that can be used here, to get a straight line

graph. 3

Q24. Define the terms (i) mass defect (ii) binding energy for a nucleus and state the

relation between the two.

For a given nuclear reaction the B.E./nucleon of the product nucleus/nuclei is

more than that for the original nucleus/nuclei. Is this nuclear reaction

exothermic or endothermic in nature? Justify your choice.

OR

56

(a) The number of nuclei, of a given radioactive nucleus, at times t=0 and t=T,

are N0 and (N0/n) respectively. Obtain an expression for the half life (T1/2) of

this nucleus in terms of n and T.

(b) Identify the nature of the ‘radioactive radiations’, emitted in each step of the

‘decay chain’ given below: 3

A

Z Z-2 Z-2 Z-1

A-4 A-4 A-4X Y Y W

Q25.

Q26. The capacitors C1, and C2, having plates of area A each, are connected in series,

as shown. Campare the capacitance of this combination with the capacitor C3,

again having plates of area A each, but ‘made up’ as shown in the figure. 3

3

Q27. (a) Write the formula for the velocity of light in a material medium of relative

permittivity r and relative magnetic permeability r. 1

3

Excessively large amount of energy is released in an uncontrolled way in

a nuclear bomb explosion. Some scientists have expressed fear that a

future nuclear war on Earth would be followed by a severe ‘nuclear

winter’ with a devasting effect on life on Earth.

Answer the following questions based on above possible scenario:

a) Name the basic principle responsible for release of large amount

of energy in a nuclear bomb explosion. How will the nuclear

bomb explosion result in ‘nuclear winter’?

b) Which two human values need to be promoted in individuals so

that such a situation of nuclear winter does not arise?

c) Suggest any one method to promote these values in school

students.

3 3

57

(b) The following table gives the wavelength range of some constituents of

the electromagnetic spectrum.

Select the wavelength range, and name the (associated) electromagnetic waves,

that are used in

(i) Radar systems for Aircraft navigation

(ii) Earth satellites to observe growth of crops. 2

Q28. A conducting rod XY slides freely on two parallel rails, A and B, with a

uniform velocity ‘V’. A galvanometer ‘G’

is connected, as shown in the figure and

the closed circuit has a total resistance ‘R’.

A uniform magnetic field, perpendicular

to the plane defined by the rails A and B

and the rod XY (which are mutually

perpendicular), is present over the region,

as shown.

(a) With key k open:

(i) Find the nature of charges developed at the ends of the rod XY.

(ii) Why do the electrons, in the rod XY, (finally) experience no net force

even through the magnetic force is acting on them due to the motion

of the rod?

(b) How much power needs to be delivered, (by an external agency), to keep

the rod moving at its uniform speed when key k is (i) closed (ii) open?

(c) With key k closed, how much power gets dissipated as heat in the circuit?

State the source of this power.

S.No. Wavelength Range

1. 1mm to 700nm

2. 0.1m to 1mm

3. 400 nm to 1nm

4. < 10 3 nm

58

OR

‘Box’ A, in the set up shown below, represents an electric device often

used/needed to supply, electric power from the (ac) mains, to a load.

It is known that Vo < Vi.

(a) Identify the device A and draw its symbol.

(b) Draw a schematic diagram of this electric device. Explain its principle and

working. Obtain an expression for the ratio between its output and input

voltages.

(c) Find the relation between the input and output currents of this device

assuming it to be ideal. 5

Q29. Define the terms ‘depletion layer’ and ‘barrier potential’ for a P-N junction

diode. How does an increase in the doping concentration affect the width of the

depletion region?

Draw the circuit of a full wave rectifier. Explain its working.

OR

Why is the base region of a transistor kept thin and lightly doped?

Draw the circuit diagram of the ‘set-up’ used to study the characteristics of a

npn transistor in its common emitter configuration. Sketch the typical (i) Input

characteristics and (ii) Output characteristics for this transistor configuration.

How can the out put characteristics be used to calculate the ‘current gain’ of the

transistor?

Q30. (i) A thin lens, having two surfaces of radii of curvature r1 and r2, made

from a material of refractive index , is kept in a medium of refractive

index . Derive the Lens Maker’s formula for this ‘set-up’

59

(ii) A convex lens is placed over a plane mirror. A pin is now positioned so

that there is no parallax between the pin and its image formed by this

lens-mirror combination. How can this observation be used to find the

focal length of the convex lens? Give appropriate reasons in support of

your answer.

OR

The figure, drawn here, shows a modified Young’s double slit experimental set

up. If SS2 SS1, = /4,

(i) state the condition for constructive and destructive interference

(ii) obtain an expression for the fringe width.

(iii) locate the position of the central fringe. 5

60

MARKING SCHEME

Q.No. Value point/ expected points Marks Total

1. From X to Y 1 1

2. The magnetic moment, associated with the

coil, is

m = Ia2

1

1

3. (i) Short wave broadcast services

(ii) Television broadcast (or microwave

links or Satellite communication)

½

½

1

4. The incident rays are not likely to be

paraxial.

1 1

5. As qa = Qa’, we have

=

and = 0o

½

½

1

6. Region BC 1 1

7. A ‘transducer’ is any device that converts

one form of energy into another

1 1

8. Zero 1 1

9. Let d and d’ be the width of the slits in the

two cases.

and q =

=

Yes, this ratio would also equal q

½+½

½

½

2

10. Total (initial) charge on all the droplets

61

= N x (4 0k r V)

Also N x r3 = R3

R = r

If V’ is the potential of the large drop, we

have

4 R x V’ = N x 4 kr x V

V’ = V = V

OR

We have net = 1 + 2

= 1 + 2

where 1= -a + c

and 2 = -b + c

net =

½

½

½

½

½

½

1

2

2

11. According to Einestein’s Equation:

Kmax = m max = –

This is the equation of a straight line having

a slope 2h/m and an intercept (on the max

axis) of Comparing these, with the

given graph, we get

= or h = and = or =

½

½

½+½

2

12. (i) decreases

(The potential gradient would increase)

½+½

62

(ii) increases

(The terminal p.d across the cell would

increase)

½+½

13. r1 = O,P =

r2 = O2 P =

V =

P.E of charge , q, at P = qV

=

½

½

½

½

2

14. (i) The maximum emf ‘ ’ generated in the

coil is,

= N B A

= N B A 2 f

= [100 x 0.01 x 0.1 x 2 ] V

= V 0.52 V

(ii) The average emf generated in the coil

over one complete revolution = 0

½

1

½

2

15. Energy of one photon = E =

E =

3.3 x 10-19 J

E1 = energy emitted by the source in one

second = 66J

number of photons emitted by the source

in 1s = n = = 2 x 1020

Total number of photons emitted by

½

½

½

63

source in 2 minutes

= N = n x 2 x 60

= 2 x 1020 x 120 = 2.4 x 1022 photons

½

2

16. Diode D1 is forward biased while Diode D2

is reverse biased

Hence the resistances, of (ideal) diodes, D1

and D2, can be taken as zero and infinity,

respectively.

The given circuit can, therefore, be redrawn

as shown in the figure.

Using ohm’s law,

I = A = 2A

current flowing in the 1 resistor, is 2A.

½

½

½

½

2

17. (a) X-Diamagnetic,

Y-Ferromagnetic

(b) X- No change

(c) Y- Decreases with temperature

18. No

-Since there is only one magnetic field, there

is no interaction and hence no force

between the two wires.

19. For circuit 1, we have, (from the Wheatstone

bridge balance condition),

64

R1 = 6

In circuit 2, the interchange of the positions

of the battery and the galvanometer, does

not change the (wheatstone Bridge) balance

condition.

=

or R2 = 4

= =

½

½

½

½

½

½

3

20. In a hydrogen atom, the energy (En) of

electron, in a state, having principal

quantum number ‘n’, is given by

En = eV

E1 = -13.6eV and E2 = -3.4 eV

It follows that the state n=2 has an

excitation energy of 10.2 eV. Hence the

electron is making a transition from n=n1 to

n=2 where (n1>2).

Now En1 – E2 =

But

En1= (-3.4 + 2.55) eV

≃ - 0.85 eV

But we also have En1 = eV

we get n1 = 4

½

½

½

½

½

½

3

21. Intensity observed by

65

(i) Observer O1 =

(ii) Observer O2 = cos2 60o

=

(iii) Observer O3 = cos2 (90o-60o)

= x =

½

½

½

1

½

3

3

22. (i) The magnetic field is perpendicular to

the plane of page and is directed inwards

(ii) In region I

=

qE = q B

E = B

(iii) In region II

= q B r =

Substituting the value of , we get

r =

Let B’ (=nB) denote the new magnetic field

in region II. If r’ is the radius of the circular

path now, we have

r1 = =

Hence radius of the circular path, would

decrease by a factor n.

½

½

½

½

½

½

3

23. See (fig 9.25, Page 332 Part II NCERT) 1

66

For a small angled prism, of refracting angle

:

Angle of deviation = where is

the refractive index of the material of the

prism.

To get a straight line graph, we need to use

and as the pair of variables.

½

1

½

3

24. (i) Mass defect ( M), of any nucleus AZ X , is

the difference in the mass of the nucleus

(=M) and the sum of masses of its

constituent nucleons (= M’).

M = M’ – M

= [ Z mp + (A- Z ) mn] –M

where mp and mn denote the mass of the

proton and the neutron respectively.

(ii) Binding energy is the energy required to

separate a nucleus into its constituent

nucleons. The relation between the two is:

B.E. = (mass defect) c2

(iii) There is a release of energy i.e., the

1

½

½

67

reaction is exothermic.

Reason: Increase in B.E/nucleon implies

that more mass has been converted into

energy. This would result in release of

energy.

OR

(a) According to the (exponential) law of

radioactive decay.

N = No

Given N=No/n and t = T

= No

or n =

=

half life 12

= =

(b)

(i) – rays

(ii) – rays

(iii) – rays

½

½

½

½

½

½

½

½

3

3

25.

3

3

a) – Uncontrolled nuclear chain reaction.

- The thick smoke produced due to nuclear explosion would

perhaps cover substantial parts of the sky preventing solar

light from reaching many parts of the Earth resulting in

lowering of atmospheric temperature.

b) - International understanding and Brotherhood.

- Love for humanity/non violence

c) - Group discussion for value clarification

- Vigorous campaign for spreading awareness using mass

media. 68

26. We have C1 =

and C2 =

Ceq = =

Now, capacitor C3 can be considered as

made up of two capacitors C1 and C2, each

of plate area A and separation d, connected

in series.

We have : C1’ =

and C2’ =

C3 = =

= 1

Hence net capacitance of the combination is

equal to that of C3.

½

½

½

½

½

½

3

27. (a)

(b) We have =

(i) Wavelength range : [0.1m to 1mm]

(Microwaves)

(ii) Wavelength range: [1mm to 700 nm]

(Infrared waves)

½+½

½+½

½+½

1

3

28. (a)

(i) X : negative , Y: positive

(ii) Magnetic force, Fm, experienced by the

moving electrons, gets balanced by the

electric force due to the electric field, caused

by the charges developed at the ends of the

½

69

rod. Hence net force on the electrons, inside

the rod, (finally) become zero.

(b) The power, that needs to be delivered by

the external agency, when key k is closed, is

P=FmV = (I l B)V = .lBV

= B2l2V2/R

When k is open, there is an induced emf,

but no induced current. Hence power that

needs to be delivered is zero.

(c) Power, dissipated as heat

= i2 R =

The source of this power is the mechanical

work done by the external agency.

OR

(a) Step down transformer.

(b) Diagram

Principle

Working

Obtaining the expression

(c) Input power = output power

Vp iP = Vs is

1+½

½+½

½

½+½

½

½

½

½

½

½

2

5

70

= = ½ 5

29. The space charge region, on either side of

the junction (taken together), is known as

the depletion layer.

The p.d across the depletion layer is known

as the barrier potential

The width of the depletion region decreases

with an increase in the doping

concentraction.

The circuit of a full-wave rectifier is shown

below.

Working details

OR

The base region of a transistor is thin and

lightly doped so that the base current (IB) is

very small compared to emitter current (IE).

½

½

½

1½

2

1

1

1

5

71

The current gain of a transistor in

common emitter configuration is

=

IC and IB can be obtained, from the two

curves, in the output characteristics.

1

1

5

72

30.

(i) Diagram

Derivation

(ii) The rays must fall normally on the

plane mirror so that the image of

the pin coincides with itself

Hence rays, like CA and DB, form a

parallel beam incident on the lens.

P is the position of the focus of the lens

Distance OP equals the focal length of

the lens

OR

= initial path different between S1 and S2

= SS2 – SS1 =

= S2P–S1P = path difference between

disturbance from S1 and S2, at point P

=

= Total path difference between the two

disturbances at P

1

2½

½

½

½

1

½

½

5

73

= + = +

For constructive interference:

= = n ; n = 0, 1, 2,….

= (n- ) …(i)

For destructive interference

= (2n-1) . . . (ii)

–

= fringe width = yn+1 –yn =

The position Yo of central fringe is obtained

by putting n=o in Eqn (i). Therefore,

yo = -

[Negative sign shows that the central fringe

is obtained at a point below the (central)

point O.]

1

1

1

5

74

pankaj

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