L.35

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PRE-LEAVING CERTIFICATE EXAMINATION, 2012

PHYSICS – ORDINARY LEVEL

TIME – 3 HOURS

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

N.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. During an experiment to investigate the laws of equilibrium, a number of weights were hung

from a metre stick. Upward forces were applied to the metre stick. A number of measurements were then taken and used to verify the laws of equilibrium.

(i) Draw a diagram of the apparatus used in the experiment showing all the forces acting on the metre stick. (9)

(ii) How were the upward forces applied to the metre stick? (4)

(iii) What measurements were taken during the experiment? (12)

(iv) Explain how the second law of equilibrium (i.e. that the sum of the moments about any axis add to zero) was verified from these measurements. (15)

2. The following is an extract from a student’s report of an experiment to verify Snell’s law of

refraction. “I drew a line along the direction of the incident ray to the glass block. I

then drew a line along the direction of the refracted ray. I constructed a normal at the point of incidence. I measured the angle of incidence and the angle of refraction. I repeated this procedure for a number of angles of incidence.”

(i) Explain using a labelled diagram how the direction of the incident ray, refracted ray

and normal were determined. (13)

(ii) Indicate on your diagram the angle of incidence and angle of refraction. (6)

(iii) Copy this table into your answer book and complete it by calculating sin i and sin r for each measurement. (6)

Angle of incidence, i / 25 35 45 55

Angle of refraction, r / 16.8 23.1 29.0 34.1

sin i

sin r

(iv) Use the data to verify Snell’s law of refraction. (15)

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3. You carried out an experiment to investigate the relationship between the fundamental frequency f of a stretched string and the length of the string l.

The following data were recorded.

Fundamental frequency, f / Hz 256 335 394 420 512

Length, l / m 0.96 0.73 0.62 0.59 0.48

l1

/ m–1

(i) Draw a labelled diagram of the apparatus you used. (12)

(ii) State one quantity that you kept constant during this experiment. (6)

(iii) Copy this table into your answer book and complete it by calculating l1

for each

measurement. (5)

(iv) Draw a graph, on graph paper, of the frequency against l1

(put frequency on the

Y-axis). (11)

(v) What does your graph tell you about the relationship between the frequency and the length of a stretched string? (6)

4. In an experiment to verify Joule’s law, a constant (1) …..……..……………….….. was passed

through a coil that was placed in water for a fixed (2) …..……..……………….….. and a measurement of (3) …..……..……………….….. was taken.

(i) Copy the above statement and complete it in your answerbook. (12)

(ii) As well as number (2) in the sentence above, state one other quantity that should be kept constant during the experiment. (6)

(iii) Draw a labelled diagram of the apparatus used to record the measurements. (15)

(iv) What values would you plot on the horizontal (X-axis) and vertical (Y-axis) axes of a graph that would verify Joule’s law? (7)

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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) State the principle of conservation of momentum. (b) A diver dives to a depth of 80 m. Calculate the

pressure on the diver due to the water. (density of water = 1000 kg m–3; acceleration due to gravity = 9.8 m s–2)

(c) State Newton’s third law of motion. (d) Which one of the following is not a property of both transverse and longitudinal waves? reflection refraction polarisation diffraction (e) Calculate the critical angle for glass of refractive index 1.45. (f) What conclusion can be drawn from a building that has a low U-value? (g) Name the electrical component which stores charge in a camera flash. (h) State two factors which affect the resistance of a conductor. (i) What is thermionic emission? (j) Identify the numbers represented by X and Y in the following alpha decay of radium.

HeRnRa 42

XY

22888

(8 × 7)

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6. Define acceleration. (6) The following velocity–time graph

represents the run of the winner of a race. (i) Using the changing shape of the graph

describe how the runner runs the race (a) for the first 30 s (b) from 30 to 150 s (c) the last 90 s. (9)

(ii) Calculate the acceleration of the runner at the start of the race and at the end of the race. (15)

(iii) Calculate the distance run by the runner in (a) the first 30 s (b) from 30 to 150 s (c) the last 90 s. (12)

(iv) Calculate the length of the race and the average speed of the runner during the race. (6)

(v) After passing the finishing line, the runner travels a distance of 50 m before she stops.

What length of time after passing the finishing line does she stop? (8)

7. (a) (i) What is latent heat? (9) (ii) Explain how latent heat helps a person to cool down when they perspire. (9) (b) A heat pump used in a refrigerator, as shown,

uses latent heat to cool the refrigerator.

(i) Explain how a heat pump causes the inside of the refrigerator to become cold. (12)

In the freezer compartment of the refrigerator,

80 g of water at 15 C is added to the ice tray.

Calculate how much energy is required (ii) to reduce the temperature of the water to 0 C (iii) to turn all the water to ice at 0 C (iv) to reduce the temperature of the ice from 0 C to –10 C. (22) (v) Why is a burn from steam at 100 C more damaging than a burn from

water at 100 C? (4) (specific latent heat of fusion of ice = 3.3 × 105 J kg–1;

specific heat capacity of water = 4180 J kg–1 K–1; specific heat capacity of ice = 2100 J kg–1 K–1)

vapour

liquid

condensor

pump

freezercompartment

0 30 60 90 180 210 240120 150time / s

velocity / m s–1

0

4

2

6

10

12

8

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8. (i) Define potential difference. (6) (ii) What is the unit of potential difference? (3) (iii) State Ohm’s law. (9) (iv) Sketch a current (I) against voltage (V) graph for a conductor that obeys Ohm’s law. (9) A current against voltage graph for a semiconductor diode is shown below.

I

V

(v) Does a semiconductor diode obey Ohm’s law? (Use the graph to explain your answer.) (9)

(vi) Draw a diagram of a circuit that could be used to produce the graph above. (15)

(vii) Give one use of a semiconductor diode. (5) 9. (i) State Coulomb’s law. (9) (ii) Draw a labelled diagram of a gold leaf electroscope. (11) (iii) Describe how a negative charge is placed on the electroscope. (12) (iv) A charged object is brought near the cap of the negatively charged electroscope

and the leaf collapses.

Is the charge on the object positive or negative? Explain your answer. (9) (v) What is point discharge? (6)

(vi) How does lightning occur? (vii) How can buildings be protected from lightning damage? (9)

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10. (i) What is the difference between nuclear fission and nuclear fusion? (12)

(ii) Name a material that could be used as a fuel in a nuclear fission reactor. (6)

(iii) In a nuclear fission reactor, what is a chain reaction?

How is a chain reaction prevented from getting out of control? (15)

(iv) What is the purpose of a moderator in a fission reactor?

Name a suitable material that can be used as a moderator. (9)

(v) Nuclear fusion occurs in the sun.

Name the gas that acts as the fuel for nuclear fusion in the sun.

What gas is produced as a result of nuclear fusion in the sun? (6)

(vi) Give two reasons why nuclear fusion is considered more environmentally friendly than nuclear fission. (8)

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11. Read this passage and answer the questions below.

Scientists have tried to explain the nature of light since the beginning of time. Newton, in the 17th century, asserted that light was formed by very tiny particles (corpuscles).

Later, Huygens stated that light was a wave, basing this affirmation on its wave-like characteristics. However Huygens believed a wave was not viable without a medium that could transmit it.

It was then the concept of “ether” (the medium) was invented. The investigators Michelson and Morley carried out experiments demonstrating that ether did not exist. While carrying out these experiments, they also demonstrated a more important fact: the speed of light is constant.

At the beginning of the 20th century, Planck and Einstein did not agree with the wave-like theory of light; rather they supported the corpuscle (particle) theory of light. They used the term “photon” to refer to an individual particle of light, travelling in a straight line when acting within dimensions larger than its wavelength.

(Adapted from http://lighttheory.com/light/history.htm)

(a) What is the difference between Newton’s and Huygen’s theories of the nature of light? (b) What was the most significant discovery of the Michelson and Morley light experiments? (c) At the start of the 20th century what name was used for individual packets or particles of

light? (d) When two waves meet, they produce a wave of amplitude greater than the amplitudes of

each of the individual waves. Name this phenomenon. (e) What is the energy of an individual packet of light energy whose frequency is

4.6 × 1014 Hz? (f) What is the wavelength of light of frequency 4.6 × 1014 Hz? (g) Light is passed through a prism. Which colour light is (i) refracted the most and (ii) refracted the least? (h) Which two primary colours are mixed to produce cyan light?

(8 × 7)

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12. Answer any two of the following parts (a), (b), (c), (d). (a) What is the difference between kinetic energy and potential energy? (6) A firework of mass 2 kg is fired vertically upwards into the air at a velocity of 50 m s–1.

(i) Explain how the kinetic energy and potential energy of the firework change

as it rises. (8)

(ii) When the potential energy of the firework has increased to 980 J, it explodes. At what height is the firework when it explodes? (6)

(iii) If the firework failed to explode, what height would it have reached? (acceleration due to gravity = 9.8 m s–2) (8) (b) State the laws of reflection of light. (9) Plane mirrors and convex mirrors can be used as car door mirrors.

(i) Why are concave mirrors not suitable for use as car door mirrors? (6) (ii) Give two uses for a concave mirror. (6) (iii) Give an advantage and a disadvantage of using a convex mirror rather than a plane

mirror as a car door mirror. (7)

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(c) What is a magnetic field? (6) Describe an experiment that demonstrates the magnetic effect of an electric current. (9)

Sketch the magnetic field due to a current flowing in a solenoid. (Include the direction of

the current.) Give two effects of placing an iron core in the centre of a solenoid. (13) (d) What are X-rays? (6) The diagram shows a simple X-ray tube.

Lowvoltage

Highvoltage

- +

(i) Copy the diagram into your answerbook and label (a) the (heated) cathode and (b) the cooling fins. (6)

(ii) Name the material used for the target. (3)

(iii) What percentage of the original energy becomes X-radiation? (3) X-rays are used to detect cracks or breaks in bones. (iv) Give another use of X-rays in medicine. (3) (v) Give a use of X-rays in industry. (3) (vi) Why do operators of X-ray machines

in hospitals need to wear protective clothing? (4)

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