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L.36

PRE-LEAVING CERTIFICATE EXAMINATION, 2016

PHYSICS – HIGHER LEVEL

TIME – 3 HOURS

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

Relevant data are listed in the Formulae and Tables booklet, which is available from the Superintendent.

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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 acceleration a of a body and the force F

applied to it, a student recorded the following data. Before the force was applied, the student tested that no other net force acted on the body.

F (N) 0.40 0.80 1.20 1.60 2.00 2.40 2.80

a (m s–2) 0.49 0.99 1.51 1.95 2.49 2.93 3.45

How could the student have tested that no other net force was acting on the body? (4) Draw a labelled diagram of the apparatus used in the experiment.

Describe how the acceleration was measured. (15) 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 body. (15) If the student had not ensured that other net forces (besides the applied force) were absent, how

would this have affected the graph? Explain your answer. (6) 2. In an experiment to verify the laws of equilibrium for a set of co-planar forces acting on a uniform

metre stick, a student attached four weights and two Newton meters to a metre stick. The positions of the weights and Newton meters were changed until the metre stick was in equilibrium. These positions, as well as the values of the weights and the force readings on the Newton meters, were recorded and are given in the table below. The mass of the metre stick was found to be 122 g.

Weight 1Newton meter 1

Weight 2 Weight 3Newton meter 2

Weight 4

Force (N) 2.0 6.9 4.0 2.0 5.3 3.0

Position on metre stick (cm) 13.0 24.0 31.0 61.0 83.0 92.0

How did the student know that the metre stick was uniform?

Why was it important that the metre stick was horizontal and the Newton meters were vertical while the measurements were being taken? (18)

Calculate (i) the net force acting on the metre stick (ii) the sum of the moments of the forces about the 0 cm mark on the metre stick.

Use these results to verify the laws of equilibrium. (22)

(acceleration due to gravity = 9.8 m s–2)

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3. 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 student then plotted the following points based on the collected data.

0.10.0 0.2 0.3 0.4 0.5 0.6 0.7 0.8

0.1

0.0

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

X

Y

Describe, with the aid of a labelled diagram, how the student measured the angle of incidence and

the angle of refraction. (9) What labels should be placed on each axis, instead of X and Y?

Why are these quantities not interchangeable for the graph above?

What is the smallest angle of incidence that the student set in this experiment? (12) Complete a suitable graph using the plotted points above.

How does the graph verify Snell’s law?

Use your graph to determine the refractive index of the glass block. (19)

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4. In an experiment to investigate how current I varied with voltage V across a copper sulfate solution with copper electrodes, a student collected the following data.

V (V) 0 1 2 3 4 5 6 7 8

I (mA) 0 53 104 157 209 262 314 366 420

Describe, with the aid of a labelled circuit diagram, how the student obtained this data. (12) Draw a suitable graph to show how this data verifies Ohm’s law for a copper sulfate solution. (15) The student then replaced the copper sulfate solution and electrodes with a semiconductor diode in

forward bias. The current for a number of different voltages across the diode was measured. Draw a sketch of the graph the student would expect to produce showing the variation of current

with voltage for the semiconductor diode.

Explain why the current varies in this way with voltage. (13)

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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) A ball of mass 500 g is rotated at the end of a string with an angular velocity of 5 rad s–1. If the tension in the string is 12 N, what is the radius of the rotation of the ball? (b) When a mercury-in-glass thermometer

is placed in melting ice, the length of the mercury column is 7 cm. When the thermometer is placed in steam above boiling water, the length of the column is 39 cm.

What is the length of the mercury column when the thermometer is placed in water at 40 C?

(c) State the law of flotation. (d) Give one advantage and one disadvantage

of using a convex mirror, instead of a plane mirror, as a sideview mirror on a car.

(e) What is point discharge? (f) Write the following electromagnetic waves in increasing order of frequency:

Microwaves infra red gamma rays visible light radio waves (g) Draw a graph showing the relationship between current and potential difference (I-V graph)

for conduction in a vacuum. (h) What is the difference between how a line spectrum and

a continuous spectrum is produced? (i) In a nuclear reaction, 17.39 MeV of energy is released. Calculate the loss of mass in the reaction. (j) State two differences between leptons and hadrons. or State the advantage of using a bridge rectifier over a single diode when converting a.c. to d.c.

current. Why is a capacitor placed in the bridge rectifier circuit?

(8 × 7)

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6. State the principle of conservation of momentum. Will kinetic energy also be conserved in all cases where momentum is conserved? Give an example to support your answer. (15)

A white snooker ball has a mass of 170 g while all other colour snooker balls have a mass of 185 g.

On a snooker table, the white ball strikes a cushion at right angles. When it rebounds at right angles it loses a quarter of its kinetic energy. It rebounds with a speed of 0.693 m s–1.

Calculate (i) the loss of kinetic energy due to the collision with the cushion (ii) the speed of the ball before the collision (iii) the change of momentum due to the collision. (20) The white ball continues with the same speed, until it collides with a black ball travelling in the

opposite direction at a speed of 0.7 m s–1. After the collision, the white ball rebounds along its original path at 0.3 m s–1.

What is the speed and direction of the black ball after the collision? (12) After rebounding from the black ball, the white ball collides

with a red ball travelling in the opposite direction with a speed of 0.6 m s–1. After the collision, the white ball is deflected through an angle of 30 and travels at 0.25 m s–1. The red ball is deflected through an angle of 12.38.

Given that after the collision, the total momentum perpendicular to the direction of the balls before

the collision is zero, what is the speed of the red ball after this collision? (9) 7. Heat is extracted from a refrigerator using a heat pump which uses specific

latent heat to extract heat from inside the refrigerator and emit it outside. What is specific latent heat? Distinguish between specific latent heat of fusion

and specific latent heat of vaporisation. (12) Explain, with the aid of a labelled diagram, how the heat pump causes the

inside of the refrigerator to get cooler. (12) Freon is an example of a refrigerant (liquid/gas circulating in the heat pump)

used in refrigerators. How much heat energy is extracted from the inside of the fridge during one heat exchange if there is 100 millilitres of Freon in the heat pump? (9)

A refrigerator of internal dimensions 50 cm × 50 cm × 100 cm is filled with milk cartons until the

milk takes up half of the volume of the refrigerator. The refrigerator is then switched on.

How much heat energy is extracted when the temperature of the refrigerator is reduced from 20 C to 3 C?

If the Freon refrigerant is circulated 10 times every minute, how long will it take for this temperature drop to occur? (19)

Why would the temperature of the refrigerator have dropped much more quickly if it had

been empty? (4)

(specific latent heat of vaporisation of Freon = 232 kJ kg–1; density of liquid Freon = 1476 kg m–3; specific heat capacity of air = 1005 J kg–1 K–1; density of air = 1.2 kg m–3;

specific heat capacity of milk = 3770 J kg–1 K–1; density of milk = 1030 kg m–3; 1 litre = 10–3 m3)

12.38°

30°

RR

W

W

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8. Define capacitance. (6) State three factors on which the capacitance of a parallel plate capacitor depends. (9) Two capacitors are connected in series as shown below.

7 µF 10 µF

24 V

Assuming the charge is the same on both capacitors, calculate (i) the charge on each capacitor. (ii) the total energy stored on both capacitors. (24)

To what capacitance should the 7 μF capacitor be changed so that the potential difference across the new capacitor is double the potential difference across the 10 μF capacitor? (8)

If the 7 μF capacitor is replaced with a 20 k resistor, calculate the charge on the 10 μF capacitor

when a current of 1 mA flows in the circuit. (9) 9. What are alpha-particles? How are alpha-particles produced? (12) Why would alpha-particles not be suitable for use in detecting thickness of objects in industry but

be suitable for use in smoke detectors? (6) In 1919, under the direction of Rutherford, alpha-particles were used in an experiment to discover

the existence of a nucleus inside the atom. Describe this experiment and explain how it showed the presence of the nucleus. (12)

Most smoke detectors that operate alarms contain the

artificially produced radioisotope americium–241, which is an alpha-emitter. It is produced in nuclear reactors and is a decay product of plutonium–241.

Explain why alpha-particles are not emitted when plutonium–241 decays into americium–241.

Write down the nuclear equation for this decay and the equation for the subsequent decay of americium–241. (15)

A typical smoke detector contains 0.29 μg of americium–241. The half life of americium–241 is 431 years.

How many alpha-particles are emitted per second in the smoke detector? (11)

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10. Answer either part (a) or part (b). (a) In the very early stages of the universe, it has been proposed that massive numbers of particles

and anti-particles were created and then proceeded to annihilate each other. Cosmic microwave radiation that was produced as a result of this pair annihilation travels through the universe today. There was a small imbalance in the amount of matter produced over anti-matter (approximately one extra matter particle for each billion matter–anti-matter particle pairs. This extra matter is what forms our universe today.

Name the scientist who proposed the existence of anti-matter based on mathematical

calculations in 1928.

Give the quark composition of a proton, a neutron and their respective anti-particles. (15) How many photons are produced when a proton and an anti-proton annihilate?

Explain why this number of photons is produced.

Calculate the minimum frequency of the photons produced during this annihilation. (18) If a photon of wavelength 5.6 × 10–16 m produces a proton–anti-proton pair, what is the speed

of the proton produced?

Why must both a proton and an anti-proton be produced? (23) (b) The structure of an NPN bipolar transistor is shown below.

n

n

p

B

C

A

Describe how the p- and n-type layers in the transistor are produced. Explain how they differ

from each other as a result. (12) Label the connections A, B and C in the transistor shown above.

If a potential difference is connected between B and C and another potential difference is connected between A and C, describe how the current flowing into the transistor at B is related to the current flowing into the transistor at A. (15)

Describe the basic principle of operation of a light-dependent resistor (LDR). (9) Draw a labelled circuit diagram containing an NPN bipolar transistor and an LDR that could

be used to switch on a light when ambient light intensity drops below a certain level.

Explain the operation of the circuit. (20)

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11. Read the following passage and answer the accompanying questions.

Scientists and engineers use destructive interference for a number of applications to reduce levels of ambient sound and noise. One example of this is the modern electronic automobile muffler. This device senses the sound propagating down the exhaust pipe and creates a matching sound with opposite phase. These two sounds interfere destructively, muffling the noise of the engine. Another example is in industrial noise control. This involves sensing the ambient sound in a workplace, electronically reproducing a sound with the opposite phase, and then introducing that sound into the environment so that it interferes destructively with the ambient sound to reduce the overall sound level.

(Adapted from www.universetoday.com, Destructive Interference)

(a) What is meant by the term interference? (b) Coherent sources are required for destructive interference to occur. What are coherent sources? (c) Give two conditions necessary for total destructive interference to occur. (d) Draw a diagram to show an interference pattern produced by two loudspeakers. Indicate the

positions of constructive and destructive interference on the diagram. (e) Why is sound intensity level, rather than sound intensity, used as the quantity to measure the

loudness of sound in sound level meters? (f) Why is the dB(A) scale used in sound level meters? (g) What is the sound intensity at a doorway of dimensions 2 m × 0.7 m if 2.4 J of sound energy

passes through the door each minute? (h) As the source of the sound moves away from the doorway, the sound intensity drops from

3.2 mW m–2 to 0.2 mW m–2 over a period of time. What is the drop in sound intensity level over the same period?

(8 × 7)

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12. Answer any two of the following parts (a), (b), (c), (d). (a) When is an object moving with simple harmonic motion? (6) An astronaut carried a simple pendulum consisting

of a small metal bob and a string set at a length of 80 cm onto the moon. The pendulum was set vibrating at small-angle oscillations.

The astronaut measured the length of time it took the pendulum to travel between a point of maximum acceleration to the next point of maximum velocity to be 1.08 s.

What is the period of the oscillation?

What would the astronaut have calculated as the acceleration due to gravity on the moon? (10) Using the same apparatus and timer, how could the astronaut have obtained a more accurate

value for the acceleration due to gravity on the moon?

Explain why this would have given a more accurate result. (6) State two differences you would have observed from the oscillations if they were repeated

on Earth. (6) (b) What is meant by the term polarisation of waves? (6) Why can light waves be polarised but sound waves cannot? (6) Describe an experiment to demonstrate the polarisation of light. (8) Give an advantage of wearing Polaroid sunglasses

when on a boat or walking near water.

Give another application of the polarisation of waves. (8)

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(c) Until the development of flat screen technology, cathode ray tubes were used in a wide range of applications, television and computer screens, oscilloscopes, ECG and EEG machines.

The principle of a cathode ray tube involves thermionic emission and the acceleration of a beam of electrons.

Distinguish between thermionic emission

and photoelectric emission. (9) Explain how a beam of electrons is produced in a cathode ray tube. (8) What is the minimum voltage required to accelerate a beam of electrons to 3 × 107 m s–1

in a cathode ray tube?

Give a reason why a higher voltage could be required for the beam of electrons to reach this speed. (11)

(d) State two factors on which the force experienced by a current-carrying conductor in a

magnetic field depends. (6) Explain why two adjacent current-carrying conductors exert a force on each other. (5) A rectangular coil of wire is free to rotate about an axis through its centre, as shown. The coil

is placed in a uniform magnetic field, with the direction of the magnetic field in the plane of the coil and perpendicular to the 12 cm length sides of the coil. A current of 5 A flows through the coil. The force exerted on the two 12 cm sides of the coil is 4.8 N.

7 cm

B12 cm

Calculate the magnetic flux density of the magnetic field.

What is the size of the force exerted on the 7 cm side of the coil due to the magnetic field when the coil has rotated through 30?

Why does this force not contribute to the rotation of the coil?

What is the size of the force on each of the 12 cm sides of the coil in this position? (17)

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