M.36

2009 M.36 1/12 Page 1 of 12

ªM.36-¬

PRE-LEAVING CERTIFICATE EXAMINATION, 2009

PHYSICS – HIGHER LEVEL

TIME – 3 HOURS

Answer three questions from section A and five questions from section B.

2009 M.36 2/12 Page 2 of 12

SECTION A (120 marks) Answer three questions from this section. Each question carries 40 marks.

1. In an experiment to investigate the relationship between the force F applied to a trolley

and its acceleration a, the following results were obtained.

F / N 0.5 1.0 1.5 2.0 2.5 3.0

a / m s–2 0.82 1.63 2.46 3.26 4.07 4.89

Describe how the force was applied and the acceleration was measured. (12) Draw a suitable graph to show the relationship between the applied force and

the acceleration. Use your graph to calculate the mass of the accelerating objects. (18) Why was it important that the mass of the system was kept constant? Explain how this was achieved. (10) 2. In an experiment to verify Snell’s law, a student measured the angle of incidence i and

the corresponding angle of refraction r for light entering a glass block. This was repeated for a number of different angles of incidence. The following data was recorded.

i / degrees 15 25 35 45 55 65

r / degrees 9 17 23 29 34 38 Describe, with the aid of a diagram, how the student measured the angle of refraction. (9) Draw a suitable graph and explain how it verifies Snell’s law. (15) Use your graph to calculate the critical angle of the glass block. (9) Which result is the least accurate? Explain your answer. (7)

2009 M.36 3/12 Page 3 of 12

3. In an experiment to investigate the relationship between the fundamental frequency f of stretched string and its tension T, a student recorded the following data.

The length of the string was kept constant at 80 cm.

T / N 10 16 19 23 26 36

f / Hz 256 325 353 389 412 486

Describe how the tension of the string was varied and measured. (6) How did the student know that the string was vibrating at its fundamental frequency and

not at a different harmonic? (9) Draw a suitable graph and explain the relationship between the frequency and the tension of

the string. (15) From your graph, find the fundamental frequency when the tension was 20 N and the length

was reduced to 40 cm. (10) 4. A student investigated the relationship between current I and potential difference V for a

copper sulfate solution.

V / V 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

I / mA 56 87 114 145 161 201 231 248 291 Explain, using a labelled diagram, how the data was collected. (12) Draw a suitable graph to demonstrate that a copper sulfate solution obeys Ohm’s Law. (15) What are suitable electrodes for this experiment? If inactive electrodes (e.g. graphite) were used instead, how would the shape of

the graph differ? Explain why the two graphs differ in shape. (13)

2009 M.36 4/12 Page 4 of 12

SECTION B (280 marks) Answer five questions from this section. Each question carries 56 marks.

5. Answer any eight of the following parts (a), (b), (c), etc. (a) State Boyle’s law. (7) (b) A ship that can travel at 50 m s–1 in still water aims in a

northerly direction. If it meets a current of 15 m s–1 going east, what is the resultant speed and direction of the boat? (7)

(c) Define sound intensity. (7) (d) What is the principle on which residual current

devices are based? (7) (e) What speed would light travel in an optical fibre

whose refractive index is 1.54? (7) (f) Calculate the angular velocity of an object on the

surface of the earth, due to the rotation of the earth about its axis. (7)

(g) Why would a mercury thermometer and a resistance thermometer give different values

for the temperature of a room? (7) (h) Why is the capacitance of a parallel plate capacitor greater than that of a single

charged plate? (7) (i) What is the maximum kinetic energy of an electron in a cathode ray tube when the

voltage between the cathode and the anode is 2000 V? (7) (j) Write down the quark structure of an anti-proton. (7)

or

State the principle on which the moving coil loudspeaker is based. (7)

(speed of light = 3.0 × 108 m s–1; charge on electron = 1.6 × 10–19 C)

2009 M.36 5/12 Page 5 of 12

6. State Newton’s second and third laws of motion. (12) Explain how Newton’s first law is a special case of Newton’s second law. (6) Using Newton’s third law, explain why a person, in a lift moving vertically upwards, exerts

a greater force on the lift floor when the lift starts moving upwards from rest than when the lift is slowing to rest. (9)

A crane cable that is capable of withstanding 22,000 N is attached by a hook to a 2,000 kg

block that is resting on the ground. The cable initially starts lifting the block at the maximum acceleration that the cable can withstand for 2 seconds. It then continues to raise the block at constant velocity for a further 5 seconds. At this time the block slips off the hook at the end of the cable.

Calculate: (i) the tension in the cable when the block is moving at constant velocity;

(ii) the maximum acceleration that the cable can withstand;

(iii) the maximum height that the block reaches above the ground. (29) (acceleration due to gravity = 9.8 m s–2) 7. Constructive interference occurs when two coherent sources are used. Explain what is meant by constructive interference and coherent sources. (12) Describe an experiment to demonstrate constructive interference for sound waves. (12) State two uses of microwaves. (6) Two single frequency coherent microwave beams are directed from the same point towards

a concave surface that reflects microwaves and is of focal length 20 cm. One beam is incident parallel to the principal axis of the concave reflector, 6 cm from the axis. The other beam passes through the focal point before striking the mirror. The strongest possible signal that could be produced by the combination of the two beams is detected where they meet, 30 cm from the concave surface.

Calculate: (i) how far from the concave surface the two beams originated;

(ii) how far below the axis the two beams met;

(iii) the minimum possible frequency of the microwaves. (26) (speed of light = 3 × 108 m s–1)

2009 M.36 6/12 Page 6 of 12

8. Define (i) potential difference, (ii) electromotive force. (12) Two resistors R1 and R2 are connected in parallel.

These in turn are connected in series with a third resistor R3.

Derive an expression for the resistance of a single resistor that could replace the two resistors in parallel and still produce the same current

flowing through R3, when a voltage supply is connected across the circuit. Derive an expression for the effective resistance of the entire circuit. (18) Draw a circuit diagram of a Wheatstone bridge, with resistors 10 Ω and 15 Ω along the top

branch of the circuit and resistors 20 Ω and 35 Ω along the bottom branch.

(i) If 12 V is connected across the Wheatstone bridge, calculate the current flowing through each resistor.

(ii) If a galvanometer is connected between the middle of the top branch and the middle of the bottom branch of the circuit, in what direction will the current flow? Explain your answer.

(iii) How can the Wheatstone bridge be balanced by replacing only one resistor with another? (26)

9. State three factors that affect the force exerted on a current carrying conductor in a magnetic

field. (9) Sketch the shape of the magnetic field due to the current in a long straight wire. (6) Define the ampere. (9) A rectangular coil of wire is free to rotate about an

axis through its centre as shown. It is placed in a uniform magnetic field of flux density 12 T. The direction of the magnetic field is in the plane of the coil and is perpendicular to two sides of the coil. The force exerted on the 6 cm length side of the coil is 2 N

Calculate: (i) the current flowing in the coil;

(ii) the moment of the force exerted on the coil about the axis;

(iii) the moment of the force when the coil has rotated through 45°;

(iv) how the moment of the force changes as the coil rotates through 90°. (23) The coil rotates through 90° in 0.1 seconds. What is the average linear velocity of a point on either of the 6 cm length sides of the coil? (9)

2009 M.36 7/12 Page 7 of 12

10. Answer either part (a) or part (b). (a) An electron is emitted from a nucleus during beta decay. Write down the nuclear

equation for this decay. (10) Name the family of particles to which electrons belong. (3) Read the following passage and answer the accompanying questions. In 1928 Paul Dirac proposed the existence of a particle that had the same mass as an

electron but with a positive charge. In 1932, Carl David Anderson of the California Institute of Technology noticed a peculiar track in a cloud chamber. A cloud chamber shows the path of charged particles that pass through the chamber deflected by magnetic fields. In the chamber, there was a circular track that looked just like the track of an electron, but it curved with the same radius in the opposite direction. Anderson concluded it was a particle with the mass of an electron and the charge of a proton.

(Adapted from “Probing the Proton”; Parker; 2008)

(i) What name was given to the positively charged electron described above? (3) (ii) What name is given to the process that produced the two particles in the cloud

chamber? (3) (iii) Why did the two particles travel in circular paths and in opposite directions? (6) (iv) Why could the positively charged particle observed in the chamber not be a

proton? (3) (v) Write a reaction to represent the production of the two particles in

the chamber. (6) (vi) Calculate the maximum wavelength of the γ-ray photon required to produce

the particles. (12) (vii) If a γ-ray, with the minimum frequency needed to produce an electron and its

antiparticle, is incident on the cloud chamber, why are no tracks observed? (6) (viii) A positively charged particle is not produced on its own. Explain why. (4) (Planck constant = 6.6 × 10–34 J s; speed of light = 3.0 × 108 m s–1;

mass of electron = 9.1 × 10–31 kg) (b) Describe how n-type and p-type silicon semiconductors are produced. Explain the

significance of the terms n-type and p-type. (12) Using a diagram, explain the operation of a p-n junction in both forward biased and

reverse biased. (12) Draw circuit diagrams showing how a.c. voltage can be converted to d.c. voltage

using (i) a half wave rectifier, (ii) a bridge rectifier. (14) Sketch the output voltage produced by (i) the half wave rectifier, (ii) the bridge

rectifier. (12) What happens in a photodiode when light shines on it? (6)

2009 M.36 8/12 Page 8 of 12

11. Read the following passage and answer the accompanying questions. Two mysterious discoveries led Marie Curie to her life’s work. In December 1895, a German

physicist, Wilhelm Roentgen, had discovered rays that could travel through solid wood or flesh. A few months later a French physicist, Henri Becquerel, discovered that minerals containing uranium also gave off rays. Roentgen’s X-rays amazed scientists, who took to studying them with great energy. They mostly ignored Becquerel’s rays, which seemed much the same, only weaker. Marie decided to investigate the uranium rays.

She began by studying a variety of chemical compounds that contained uranium and discovered

that the strength of the rays that came out depended only on the amount of uranium in the compound. It had nothing to do with whether the material was solid or powdered, dry or wet, pure or combined with other chemical elements. If you had a certain amount of uranium, i.e., a certain number of uranium atoms, then you got a certain intensity of radiation. Nothing else made a difference.

(Adapted from “Marie Curie – Her Story in Brief”; The American Institute of Physics; 2008)

(a) What is the nature of Roentgen’s X-rays? (7) (b) How do α-rays and γ-rays differ from X-rays? (7) (c) 238

92 U undergoes three alpha decays and two beta decays. What is the atomic number and mass number of the element produced? (7) (d) “Marie Curie…discovered that the strength of the rays that came out depended only on

the amount of uranium in the compound”. How is this statement related to the law of radioactive decay? (7) (e) Define the unit named after Henri Becquerel and state the quantity for which it is

a unit. (7) (f) 235

92 U emits α-particles and has a half life of 7 × 108 years. How many α-particles are emitted per second from a sample of U-235 that contains

2 × 1020 atoms? (7) (g) Compare the ionising and penetration properties of α-rays and γ-rays. (7) (h) Marie Curie suffered health problems, eventually leading to her death, as a result of

long term exposure to the radioactive element radium. State two ways in which radiation is a health hazard. (7)

2009 M.36 9/12 Page 9 of 12

12. Answer any two of the following parts (a), (b), (c), (d). (a) Define simple harmonic motion. (9) An object of mass 2 kg is executing simple harmonic motion. It experiences a force

of 8 N when the potential energy of the object is a maximum. The next time the object has maximum potential energy is 1 second later.

Calculate: (i) the period of the oscillation;

(ii) the amplitude of the motion;

(iii) the force felt by the object when it is midway between the positions of maximum and minimum potential energy. (19)

(b) Define heat capacity. (6) State the principle on which a storage heater is based. (6) Calculate the heat capacity of a cylindrical piece of copper of height 50 cm and

radius 30 cm. (8) The piece of copper at 25 °C is placed in 100 kg of water at 80 °C in an insulated bath.

Calculate the final temperature of the water. (8) (specific heat capacity of water = 4200 J kg–1 K–1; specific heat capacity of copper = 390 J kg–1 K–1; density of copper = 8920 kg m–3) (c) State Lenz’s law. (6) Explain why violating Lenz’s law violates the law of conservation of energy. (6) A magnet is moved at 8 m s–1 towards a coil of wire of resistance 10 Ω. If the magnet

experiences a force of 0.1 N, calculate the current induced in the coil due to the moving magnet.

Why can the current flowing in the coil be different to this calculated value? (16) (d) What is the photoelectric effect? (6) Describe an experiment to demonstrate the photoelectric effect. (9) Photons of wavelength 200 nm are incident on a zinc plate whose work function is

4.3 eV. What is the energy of the photons? What is the maximum kinetic energy of the emitted photons? Why are all electrons not emitted at this maximum kinetic energy? (13) (Planck constant = 6.6 × 10–34 J s; speed of light = 3 × 108 m s–1;

charge on electron = 1.6 × 10–19 C)

2009 M.36 10/12 Page 10 of 12

Blank Page

2009 M.36 11/12 Page 11 of 12

Blank Page

2009 M.36 12/12 Page 12 of 12

ªM.36-¬

Blank Page