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PRE-LEAVING CERTIFICATE EXAMINATION, 2009

PHYSICS – ORDINARY LEVEL

TIME – 3 HOURS

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

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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 fundamental frequency of a stretched

string and its length, the following data was collected:

l / m 0.90 0.71 0.65 0.59 0.56 0.47

f / Hz 256 325 353 389 412 486 (i) Draw a labelled diagram of the apparatus used in this experiment. Indicate on the diagram

where the length was measured. (15) (ii) How was the frequency of the stretched string measured? (6)

(iii) Calculate length

1 for each data point. Plot a graph of frequency against length

1 .

Put length

1 on the horizontal axis (X-axis). (13)

(iv) What does the graph tell you about the relationship between frequency and length? (6) 2. A student carried out an experiment to measure the focal length of a convex lens. An illuminated

object was placed at a distance u from the lens and the image distance v measured. This procedure was repeated for a number of object distances. The table shows the data recorded.

object distance, u / cm 20 25 30 35 40

image distance, v / cm 59 38 30 26 24 (i) Draw a labelled diagram of the apparatus used in this experiment. Indicate the distances u

and v on the diagram. (12) (ii) State two observations the student could have made about the image formed when the object

was placed 20 cm from the lens, apart from the fact that the image is formed 59 cm from the lens. (6)

(iii) Calculate an average value for focal length of the convex lens f using the above data and the

formula vuf111 += . (16)

(iv) Why did the student not place the object at 10 cm from the lens? (6)

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3. You carried out an experiment to verify Boyle’s law for a fixed mass of gas. (i) Draw a labelled diagram of the apparatus that could be used in this experiment. (12) (ii) What measurements were taken during the experiment? (6) (iii) How did you ensure that the mass remained fixed during the experiment? (4) (iv) What other quantity had to be kept constant during the experiment? Explain how this was achieved. (9) (v) State Boyle’s law and explain how the data you collected could verify it. (9) 4. A student completed an experiment to measure the resistivity of a nichrome wire. The following is

an extract from his report. I stretched the wire to remove kinks. I attached crocodile clips to the wire and measured

the distance between the crocodile clips. I inserted wires in the crocodile clips and connected the wires to an ________________ to measure the resistance of the wire. I measured the diameter of the wire at 5 different points along the wire using a _________________. I calculated the cross sectional area of the wire using A=πr2. I

calculated the resistivity of the wire using l

RA=ρ . The following is the table of results

that I obtained.

resistance of wire between crocodile clips / Ω 22.1

length of wire between crocodile clips / mm 790

diameter of the wire / mm 0.24 0.25 0.26 0.24 0.25 (i) Fill in the spaces in the student’s report. (6) (ii) Why were the kinks removed from the wire? (4) (iii) Why did the student not measure the total length of the wire, only the distance between the

crocodile clips? (6) (iv) Using the data in the table, calculate the cross-sectional area of the wire. (12) (v) Calculate the resistivity of nichrome. (9) (vi) Why was a metre stick not used to measure the diameter of the wire? (3)

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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 Newton’s first law of motion. (7) (b) What is the momentum of a car of mass 200 kg travelling at (7)

a velocity of 70 m s–1? (P = mu) (c) What property of a musical note varies with (i) amplitude, (ii) frequency? (7) (d) What is dispersion? (7) (e) Draw a diagram showing how an image is formed in a plane mirror. (7) (f) What is the unit of capacitance? (7) (g) What is the total resistance of the circuit shown? (7)

(21

111RRR

+= )

(h) Give two properties of the electron. (7) (i) What instrument is used to measure the density of a liquid? (7) (j) What is the function of a transformer? (7)

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6. Define the moment of a force. What is a lever? (12) Explain why it is an advantage to have long handles on a wheelbarrow. (6)

Two children, one of mass 50 kg and the other of mass 30 kg, sit on either end of a seesaw, both 1.5 m from the fulcrum.

(i) What is the weight of each child? (6)

(ii) What is the moment of each child about the fulcrum? (12)

(iii) Where should the 50 kg child move to in order for the seesaw to be balanced? (9)

(iv) If both children stay at the ends of the seesaw, where should a third child of mass 30 kg sit so that the seesaw is balanced? (11)

(W = mg , M = fd, acceleration due to gravity = 9.8 m s–2)

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7. When a person perspires, they are cooling down due to latent heat.

(i) What is latent heat? (9)

(ii) Explain how perspiring helps to cool a person down. (6)

(iii) What change of state occurs during perspiration? (3) (iv) What is the difference between latent heat of vaporisation and latent heat of fusion? (9)

(v) In the above diagram, which sections represent latent heat of vaporisation and

latent heat of fusion? (6) A 200 g piece of ice at 0 °C is added to a container of water at 20 °C. The temperature of the water

eventually settled at 10 °C. Assuming that no heat is lost to the surroundings, Calculate:

(i) the heat required to melt the ice;

(ii) the heat required to raise the temperature of the melted ice from 0 °C to 10 °C;

(iii) the heat lost by the water;

(iv) the mass of the water. (23) (Q = ml, Q = mc∆θ; specific latent heat of fusion of ice = 3.3 × 105 J kg–1;

specific heat capacity of water = 4200 J kg–1 K–1.)

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8. What is meant by the refraction of light? State the laws of refraction of light. (15) A person looking at a still lake observes a fish under the water. (i) Why does the fish appear to be less deep than it actually is? (9)

(ii) If the fish is at a depth of 2 m but it appears to be at a depth of 1.5 m, what is the refractive index of water? (6)

A person scuba diving underwater can only see through a

certain circle out of the water due to total internal reflection.

(i) What is total internal reflection? (ii) Describe an experiment to demonstrate total internal

reflection. (iii) An optical fibre is an example of the application of total

internal reflection. What is the smallest angle that light must be incident on the inside surface of the optical fibre, if the light is to be totally internally reflected? The material of the optical fibre has a refractive index of 1.54. (26)

(C

ndDn

sin1, == )

9. What are magnetic field lines? (6) Draw the magnetic field around:

(i) a bar magnet;

(ii) a long straight wire carrying a current. (12) Describe an experiment that shows the magnetic field due to current in a long straight wire. (12) In an electric motor a magnetic field of flux density 4 T strikes the 10 cm side of the coil at right angles. The coil carries a current of 5 A and is free to rotate around the axis shown.

(i) What is the size of the force on either of the 10 cm sides of the coil? (9)

(ii) Draw a diagram showing the direction of

the forces on the coil. (6)

(iii) What is the size of the force exerted on the 5 cm side of the coil? Explain your answer. (6)

(iv) In a practical motor, why is there a large numbers of turns in the coil? (5) (F = BIl)

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10. In a nuclear reactor, a large amount of energy is released by nuclear fission of uranium or plutonium.

Explain the principle of nuclear fission. What particles are used to cause fission of uranium or plutonium? (12)

Explain the function of each of the following in a nuclear reactor: (i) moderator;

(ii) control rods;

(iii) shielding. (15)

State two ways that nuclear fusion has an adverse effect on the environment. (6)

The sun’s principal source of energy is nuclear fusion. The amount of heat produced is sufficient to keep the reaction going and the amount of fuel available will last for billions of years.

What is nuclear fusion? (9)

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

How does E = mc2 explain where the energy released from the sun comes from? (8)

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11. Read this passage and answer the questions below.

At any given moment, there are 1,800 thunderstorms in progress somewhere on the earth. A thunderstorm forms in air that has three components: moisture, instability and something such as a cold front to cause the air to rise. Continued rising motions within the storm may build the cloud to a height of 35,000 to 60,000 feet (6 to 10 miles) above sea level. Temperatures higher in the atmosphere are colder; ice forms in the higher parts of the cloud. Ice in a cloud seems to be a key element in the development of lightning. Storms that fail to produce quantities of ice may also fail to produce lightning.

In a storm, the ice particles vary in size from small ice crystals to larger hailstones, but in the rising and sinking motions within the storm there are a lot of collisions between the particles. This causes a separation of electrical charges. Positively charged ice crystals rise to the top of the thunderstorm, and negatively charged ice particles and hailstones drop to the middle and lower parts of the storm. Enormous charge differences (electrical differential) develop.

(Adapted from the US National Weather website)

(a) Fahrenheit is one unit of temperature. Name two other units of temperature. (7) (b) Why do positive and negative charges position themselves at opposite sides of the cloud? (7) (c) Draw a diagram showing the electric field produced due to a positive and a negative charge

near each other. (7) (d) Charge is placed on the conducting solid below. Show how the charge is distributed on this

conductor. (7) (e) Why should you stop playing golf during a lightning storm? (7) (f) Why are lightning conductors placed on buildings? (7) (g) Name two quantities on which the force between two charges depends. (7) (h) Why should a person working with integrated circuits be connected to Earth? (7)

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12. Answer any two of the following parts (a), (b), (c), (d). (a) Define energy. (6) What energy conversion takes place in an electric motor? (6) A cannon ball of mass 20 kg is fired vertically upwards from a cannon so that the ball rises to a height of 50 m. What is the potential energy gained by the ball? (6) At what velocity did the ball leave the cannon? (7) At what speed does the ball hit the cannon on the way down? (3) (P.E.= mgh, v2 = u2 + 2as, acceleration due to gravity = 9.8 m s–2) (b) Define (i) activity and (ii) half-life of a radioactive substance. (12) State one use of radioisotopes. (4) The half life of radioactive isotope is 2 years.

(i) How many half lives are there in 10 years?

(ii) What fraction of the original sample remains after 10 years?

(iii) How long does it take so that the sample has decayed to 1/8 of its original size? (12)

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(c) In Ireland, mains electricity is supplied to homes at 230 V a.c.

What is an electric current? (6) An electric fire has a power rating of 3 kW when connected to mains voltage. The fuse in the

plug was found to be a 5 A fuse. Calculate the current that flows when the electric fire is first plugged in. (9) With high voltage present in a house circuit several safety precautions must be taken.

Miniature circuit breakers and residual circuit breakers are devices often found in a house. Explain the principle on how one of these circuit breakers work. (7)

If mains voltage is supplied to a heater of resistance 50 Ω, what is the a.c. current flowing

through the heater? (6) (V = IR) (d) Light waves are transverse, electromagnetic waves while sound waves are longitudinal, mechanical waves. (i) What is the difference between transverse and longitudinal waves? (9) (ii) Name two other electromagnetic waves. (6) (iii) What is a polarised wave? (6) (iv) Sound waves can not be polarised. Explain why. (4) (v) Give an application of polarisation. (3)

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