physics seminar i

8/13/2019 Physics Seminar i

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ST. DENIS SEBUGWAWO S.S GGABA

UACE

INTERNAL SEMINAR OCTOBER 2013

PHYSICS I

SECTION A

1. (a) Define the term impulse. (1mk)

(b) A bullet of mass 300g travelling horizontally at a speed of 81 hits a body ofmass 450g moving in the same direction as the bullet at 1.51. The bullet andbody move together after collision. Find the loss in kinetic energy. (6mks)

(c) (i) State the work energy theorem. (1mk)

(ii) A ball of mass 500g at speed 101 at 60 to the horizontal strikes avertical wall and rebounds with the same speed at 120 from the original

direction. If the ball is in in contact with the wall for 8 103

, calculate the

average force exerted by the ball (6marks)

(d) State the laws of kinetic friction (3marks)

(ii) Describe a simple experiment to determine the coefficient of kinetic friction

between two solid surfaces. (3mks)

2. (a) What is meant by a conservative force? Give two examples (2mks)

(b) (i) Sketch the terms damped and forced oscillations. (4mks)

(ii) Sketch displacement-time graphs for under damped and over damped

oscillations. (2mks)

(c) A mass of 0.5kg is suspended from the free ends of two springs of force constants

100Nm-1 and 50Nm-1 respectively as shown in figure below.

Calculate the:

(i) extension produced, (3mks)(ii) tension in each spring, (2mks)

(iii) energy stored in the springs (3mks)

(iv) frequency of small oscillations when the mass is given a small vertical

displacement (4mks)


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3. (a) State what is meant by the following;

(i) Angular velocity (1mk)

(ii) Period (1mk)

as applied to oscillatory motion.

(b) Derive an expression for the acceleration of a body moving along a horizontal

circular path with uniform speed. (5mks)(c) (i) Find an expression for the period of a satellite which moves in a circular orbit

of radius r about a planet of mass M. (4mks)

(ii) Explain the meaning of a parking orbit as applied to communication via

satellite. (2mks)

(d) The period of oscillation of a conical pendulum is 2.0s. If, the string makes an angle

of 60 to the vertical at the point of suspension, calculate the

(i) vertical height of the point of suspension above the circle (3mks)

(ii) length of the string (2mks)

(iii) velocity of the mass attached to the string (2mks)

4. (a) (i) Define coefficient of viscosity and determine its dimensions. (4mks)

(ii) Explain the effect of temperature on the viscosity of liquids and gases.

(3mks)

(b) Write down Bernoullis equation for fluid flow, defining all symbols used. (3mks)

(c) A venture meter consists of a horizontal tube with a constriction which replaces part

of the piping system as shown in figure below.

If the cross-sectional area of the main pipe is 5.81 1032 and that of theconstriction is 2.58 1032, find the velocity 1, of the liquid in the main pipe.

(6mks)

(d) Explain the origin of the lift on an aeroplane at take-off. (4mks)

V. (a) Explain the terms terms laminar flowand turbulent flow. (04mks)

(b) (i) Sketch the velocity-time graph for the motion of an oil drop in air. (1mk)

(ii) Find the terminal velocity of an oil drop of radius 2.5x10-6m which falls

through air. Neglect the density of air. [Viscosity of air = 1.8x10-5Ns m-2,

density of oil = 900km m-3) (4mks)

(c) (i) Distinguish between static and dynamic pressure (2mks)

(iii) derive the expression for pressure exerted by at depth, , below the freesurface of a liquid of density, . (3mks)


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(ii) Explain why the velocity of a liquid at a wide part of a tube is less than that at

a narrow part. (2mks)

(d) (i) Define the term surface tension. (01mk)

(ii) Calculate the work done against surface tension forces in blowing a soap

bubble of diameter 15mm, if the surface tension of the soap solution is 3.0 x

10-2Nm. (03mks)

SECTION B

5. (a) Define thermal conductivity of a material and derive its dimensions. (3mks)

(b) (i) Explain, using the molecular theory of matter the mechanism of heat

conduction in non metallic solid. (3mks)

(ii) Explain briefly why metals are good conductors of heat. (2mks)

(c) (i) with the aid of a diagram, describe how you would determine the coefficient

of thermal conductivity of a good conductor of heat using Searles method.

(6mks)(ii) State the major source of error in this method (1mk)

(d) Three rods of equal lengths and equal cross-sectional areas are connected in series.

Their thermal conductivities are in the ratio of 2:4:3. If the open ends of the first and

the last rods are at temperatures 200C and 18C respectively in the steady state,

calculate the temperatures of both the junctions. (5mks)

6. (a) (i) State four differences between a real and an ideal gas. (3mks)

(ii) What is meant by kinetic theory of matter? (2mks)

(iii) Use the kinetic theory to account for the increase in pressure of a gas when its

temperature is increased at constant volume. (3mks)(b) Derive the expression

= 132

for the pressure of an ideal gas of density and mean square speed, 2(c) (a) (i) What is meant by isothermal and adiabatic changes?

(02mks)

(ii) State the conditions under which the changes in (a) (i) above take

place. (4mks)

(d) An ideal gas is trapped in a cylinder by a movable piston. Initially it occupies a

volume of 8 x 10-3

m3

and exerts a pressure of 108kPa. The gas undergoes anisothermal expansion until its volume is 27 x 10 -3 m3. It is then compressed

adiabatically to the original volume of the gas. Calculate the final pressure of the gas.

(the ratio of the principal molar heat capacities of the gas = 5:3) (6mks)

7. (a) (i) Define specific heat capacity of a substance. (1mks)

(ii) State how heat losses are minimized in calorimeter. (02mks)


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(b) (i) What is meant by a cooling correction? (01mk)

(ii) Explain how the cooling correction may be estimated in the determination of

the heat capacity of a poor conductor of heat by the method of mixtures.

(05mks)

(iii) Explain why a small body cools faster than a larger one of the same material.

(04mks)(c) Describe how you would determine the specific heat capacity of a liquid by the

continuous flow method. (07mks)

VIII. (a) (i) What is meant by a black body? (01mk)

(ii) Describe how an approximate black body can be realized in practice.

(02mks)

(b) (i) Draw sketch graphs to show variation of relative intensity of black body

radiation with wavelength for three different temperatures. (02mks)

(ii) Describe the features of the sketch graphs in (c) (i) above. (03mks)

(c) Two ideal black-bodies P and Q at temperatures 227C and 327C respectively areplaced in an evacuated enclosure whose walls are blackened and kept at 27C.

Compare their rates of loss of heat. (04mks)

(d) Explain briefly the occurrence of the following

(i) land breeze (03mks)

(ii) green house effect (03mks)

(e) State one effect of the following radiations on matter,

(i) X-rays,

(iii) Radiowaves. (2mks)

IX. (a) (i) State two qualities of a good thermometric property. (02mks)(b) (i) Describe the structure of a thermocouple thermometer. (04mks)

(ii) The thermoelectric thermometer with one junction at 0, gives an emf of0.65 mV when the second junction is at 100 and 3.92mV when at thetemperature of a boiling substance. Calculate the value of this temperature on

the scale of the thermometer. (04mks)

(iii) State one advantage of using a thermocouple thermometer. (01mk)

(c) (i) Define molar heat capacity at constant pressure. (01mk)

(ii) Explain why the molar heat capacity of an ideal gas at constant pressure,p

C

differs from the molar heat capacity at constant volume,v

C (03mks)

(iii) Derive the expression p vC C R for 1 mole of a gas, where is theuniversal gas constant. (05mks)


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SECTION C

8. (a) (i) Explain what is meant by photoelectric effect. (1 mark)

(ii) State the laws of photo electric emission (4 mark)

(b) Ultra violet and infrared radiations are directed in turns onto a zinc plate which

is attached to a gold leaf electroscope as shown in fig below:

Zinc Plate

Radiation

Gold leaf

electroscope

` Explain what happens when

(i) Ultra radiation falls on the zinc plate (1 marks)

(ii) Infrared radiation falls on the zinc plate (1 mark)

(iii) The intensity of each radiation is increased (2 marks)

(c) With the aid of a well labeled diagram, describe how stopping potential of ametal can be measured (5 marks)

(d) (i) Write down Einsteins photo electric equation defining all thesymbols used.

(2 marks)

(ii) Sodium has a work function of 2.0and is illuminated by radiation of wavelength 150. Calculate the maximum speed of the emitted electrons.

(3 marks)

9. (a) (i) What is meant by mass defect in nuclear physics (1mark)

(ii) Sketch the graph showing how binding energy per nucleon varies with

mass number and explain its main features (5marks)

(iii) Find the binding energy per nucleon of56

26Fe given that

Mass of 1 proton = 1.007825Mass of 1 neutron = 1.008665

1= 931(3marks)


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(b) (i) With the aid of a well labeled diagram explain the working of a GM tube

(5marks)

(ii) Describe how you would use the GM tube to determine the half-life of a

radio active sample (3marks)

(iii) Explain the meaning of the following as applied to GM tube: threshold

potential difference, dead time and a quenching agent . (3marks)

10. (a) What is meant by unified atomic mass unit (1mark)

(b) (i) Distinguish between nuclear fusion and nuclear fission (2 marks)

(ii) State the conditions necessary for each of the nuclear reactions in (b) (i) to

occur (2marks)

(c) (i) With the aid of a labeled diagram, describe the operation of an ionization

chamber (5marks)

(ii) Sketch the curve of ionization current against applied pd and explain its

main features (4marks)

(d) (i) Define the term Avogadros constant (1marks)(ii) A typical nuclear reaction is given by92235 +01 04295 + 57139 + 201 + 710 Calculate the total energy released by 1g of uranium (5marks)

Mass of 01 = 1.009Mass of 10 = 1.00055Mass of 04295 = 94.906Mass of 57139 = 138.906Mass of 92235 = 235.044

1

= 1.66 10

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XI. (a) (i) Explain the observation made in the Rutherfords scatteringexperiment

(ii) Why is a vacuum necessary in this experiment?

(b) (i) Distinguish between excitation and ionization energies of an atom

(ii) Describe and explain the differences between the tracks formed in

diffusion cloud chamber by alpha, beta and gamma particles

(c) (i) Define the terms half life and decay constant as applied to radioactivity.

(ii) Derive the relationship between half life and decay constant?

(d) The radio isotope60

Co decays by emission of a - particles and -ray. Its half lifeis 5.3years.


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(i) Find the activity of a source containing 0.10g of60

Co .

(ii) In what ways do -rays differ from - particles?(e) The figure shows some of the energy levels of neon. Determine the wavelength of the

radiation emitted in an electron transition from E4to E3. In what region of the electro-

magnetic spectrum does the radiation lie? .. 04 .. 0.813 .. 2.772 .. 4.871 .. 21.47XII. (a) (i) Describe with the aid of a well labeled diagram, the structure and mode of

operation of a CRO. (6 marks)

(ii) State the advantages of CRO over a moving coil meter (2 marks)

(b) In the determination of the electron charge by Millikans method, a p otentialdifference of 1.5 is applied between horizontal metal plates, 12apart. Withthe field switched off, a drop of oil of mass 1.0 1014is observed to fall withconstant velocity, 4.0 1041 between two metal plates, the drop rises withconstant velocity of 8.0 1051. How many electron charges are there on thedrop? (Assume air resistance is proportional to the velocity of the drop and neglect

air buoyancy). (5 marks)

(c) Explain why:

(i) The apparatus in Millikans experiment is surrounded with a constant

temperature enclosure (3 marks)

(ii) Low vapour- pressue oil is used (2 marks)(d) In Millikans experiment, the radius, r of the drop is calculated from

=92

Where is the viscosity of air and is the density of oil. Identify the symbol and describe briefly how it is measured. (2 marks)

XIII. (a) (i) What are X-rays? (1mk)

(ii) Explain the main design features of x-ray tube that makes it suitable for the

production of x-rays in an x-ray tube. (3mks)(iii) Explain how the intensity and penetrating power of X-rays produced by an x-

ray tube can be varied. (3mks)

(iv) State two differences between soft and hard x-rays. (2mks)

(b) (i) State Braggs law of x-ray diffraction. (1mk)

(ii) State two conditions under which X-ray diffraction occurs. (2marks)


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physics seminar i

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