Cambridge GCE O Level: Physics

Modified from Paper 1, May/June 2010


1. Energy is measured in joules. What is the correct symbol for millions of joules?
  1. mj
  2. mJ
  3. Mj
  4. MJ
m is milli, or 0.001.

M is mega, or 1 million.

The unit for joules is J, not j.

So 1 MJ is 1 million joules.

2. Which of the following is about vectors?
  1. A bird flies north for 20 km.
  2. A girl runs round a garden at 2 m/s.
  3. A worm crawls at 2 mm/s straight towards an apple.
  4. A student wanders for 5 km around town.
  1. 1 and 2
  2. 1 and 3
  3. 2 and 3
  4. 2 and 4
Vector has direction.

Only 1 and 3 have specific directions given.

3. A boy measures the speed of a toy car. At one time, it is at 1 m/s. After 2 s, it is 4 m/s. What is the acceleration?
  1. 1.5 m/s²
  2. 2.5 m/s²
  3. 3.5 m/s²
  4. 4.5 m/s²
Acceleration = change in velocity / time taken.

change in velocity = 4 - 1 = 3 m/s.

time taken = 2 s

Acceleration = 3 / 2 = 1.5 m/s².

4. This graph shows the movement of a bicycle.

What is the area under the graph?
  1. acceleration
  2. speed
  3. distance
  4. time
The area under a speed-time graph is the distance travelled.

5. A girl stands on a chair and drops a stone and a piece of paper at the same time and from the same height.

Why does the stone fall faster than the paper?
  1. The stone feels a larger air resistance.
  2. The stone has a larger mass.
  3. The paper feels larger air resistance.
  4. the paper has not reached terminal velocity.
If there is no air, both paper and stone would fall equally fast, because the acceleration of free fall is the same for both.

Air gives air resistance. This is larger for the paper, because the paper has a larger area. This cancels off some of the force of gravity.

So the paper has a smaller acceleration. So the stone falls faster.





6. An aeroplane turns right in the air. Which is the resultant force direction?

  1. A
  2. B
  3. C
  4. D
If the plane is flying straight, there are only the weight C and the lift B. These balance and the resultant is zero.

When the plane turns, it tilts. The lift changes direction to A.

The simple way to think about the motion. Since it is still going horizontally, there is no upward or downward force.

Since it is turning to the right, the force must point to the right. This means a horizontal force. D is the only option.

7. A boy climbs a very tall mountain with his father. What happens to his mass and weight?
  1. Mass decreases. Weight decreases.
  2. Mass increases. Weight increases.
  3. Mass unchanged. Weight decreases.
  4. Mass unchanged. Weight increases.
Mass is the amount of matter in a body. We may think of this as the number of atoms. Since the number of atoms does not change when the body moves to another place, the mass does not change.

(If the boy eats or urinates, his mass would change. We shall ignore this.)

At the peak of a tall mountain, the boy is further from the centre of the Earth. The force of gravity would be weaker. Soo the weight is smaller.

8. A wooden board is hinged at one end to a wall, and supported at the other end on a chair

The chair pushes up at the board with 15 N. Gravitational field strength = 10 N/kg. What is the mass of the board?
  1. 1.5 kg
  2. 3 kg
  3. 30 kg
  4. 150 kg
The hinge is the pivot.

The 15 N force gives an anti-clockwise moment, 15 N x 60 cm.

The weight gives a clockwise moment, weight x 30 cm.

The principle of moments states that these must be equal: weight x 30 = 15 x 60.

So weight = 15 x 60/ 30 = 30 N.

Since weight = mass x Gravitational field strength, or W = mg,

mass = weight / Gravitational field strength = 30 / 10 = 3 kg.

9. This is the graph for an elastic rod.

Where is the limit of proportionality?
  1. O
  2. OP
  3. P
  4. PQ
For small loads, the extension is at first proportional to the load. This means that the graph is a straight line. This is Hooke's law.

When the load gets too big, the graph starts to curve. The point where this happens (P) is called the limit of proportionality.

10. Five blocks of wood have the same mass but different shapes. They are all on a table. Which graph shows the pressure of the block on the table plotted against the base area?

  1. A
  2. B
  3. C
  4. D
pressure = force / area

In this case, force is the weight. So

pressure = weight / area

Since mass is the same for all the blocks, weight is also the same.

Since pressure = weight / area

when area increases, pressure decreases.

Graphs C and D shows this behaviour.

Let x be area and y be pressure. Consider the example when weight = 1.

Then pressure = weight / area

becomes y = 1/x.

This is a curve, not a straight line. We can check this by trying out a few values of x. E.g. when

x = 1, 2, 4
y = 1, 0.5, 0.25

Plot this, and you can see it is not straight. So it cannot be C.





11. This is a water manometer.

What is the pressure of the gas?
  1. 18 cm of water below air pressure
  2. 9 cm of water below air pressure
  3. 9 cm of water above air pressure
  4. 18 cm of water above air pressure

The pressure at A is the gas pressure.

This is the same as the pressure at B, since B is at the same level as A.

B is 18 cm below C. C is at air pressure. So the pressure at B is 18 cm below air pressure.

A has the same pressure as B. So A, and therefore the gas, is 18 cm below air pressure.

12. A lump of crushed paper is falling at a constant speed. What energy change is taking place?
  1. kinetic energy to potential energy
  2. kinetic energy to heat
  3. potential energy to kinetic energy
  4. potential energy to heat
When a body falls, it loses potential energy.

Normally, the body accelerates and gains kinetic energy.

In this case, the paper falls at the same speed, so potential energy is not converted into kinetic energy.

Since energy is conserved, the disappearing potential energy has to be converted into some other form.

In this case, it changes to heat.

13. A power supply gives 216 000 000 J of electricity in 12 hours. What is its power?
  1. 5000 W
  2. 200 000 W
  3. 15 000 000 W
  4. 216 000 000 W
power = energy / time

These quantities must be in SI units. So hours must first be converted into seconds.

12 hours = 12 x 60 x 60 seconds

So power = (216 000 000 J) / (12 x 60 x 60 s)

14. If your hand is wet, the water on you hand evaporates and its temperature changes. How does the water temperature change and why?
  1. decreases, because molecules with less energy leaves
  2. decreases, because molecules with more energy leaves
  3. increases, because molecules with less energy leaves
  4. increases, because molecules with more energy leaves
The molecules in water move at different speeds.

At the water surface, molecules with enough kinetic energy can escape into the air.

The total energy in the remaining water molecules decreases.

So temperature decreases.

15. I put some ice on the top shelf in a cupboard. The air around the ice cools down. How does the density and position of this air change?
  1. decreases, and sinks
  2. decreases, and stays at the same place
  3. increases, and sinks
  4. increases, and stays at the same place
Cold air contracts. Since the volume decreases, density increases.

As density of the cold air is higher than the density of the surrounding air, the cold air sinks.





16. A lump of ice is 15 g. It is at 0 °C. Heat goes into the ice at 2.4975 J/s from the surroundings. The specific latent heat of fusion is 333 J/g. How long does it take to melt?
  1. 35.5 s
  2. 55.5 s
  3. 2000 s
  4. 3120 s
latent heat = specific latent heat x mass

total heat needed to melt the ice = 333 J/g x 15 g

2.4975 J of heat goes into the ice in 1 s.

so time taken = total heat / 2.4975 J = 333 x 15 / 2.4975 seconds

17. Zinc and iron are used to make a bimetallic strip.

Zinc expands more when hot. What is the new shape?

  1. A
  2. B
  3. C
  4. D
The zinc strip becomes a bit longer than the iron strip.

B is the only case where this is true.

18. Which of these show a longitudinal wave?

  1. A
  2. B
  3. C
  4. D
A is the sun. It refers to light wave, which is transverse.

B is a person shouting. This refers to sound wave, which is longitudinal.

C is swinging the end of a horizontal string up and down. This gives a transverse wave.

D is the wave on water surface. This is transverse.

19. A piece of paper has these letters:

What does it look like in a mirror?

  1. A
  2. B
  3. C
  4. D
The image in a mirror is laterally inverted.

This means left becomes right, and right becomes left.

Imagine drawing a vertical line down the middle of the object [VHL], and rotate this 180°.

The result is B.

20. A light ray goes through a glass block as shown:

What is the refractive index?
  1. 1.24
  2. 1.40
  3. 1.50
  4. 1.60
refractive index, n = sin i / sin r

where i = incident angle, r = refracted angle.

This refers to light going from air into glass.

If we reverse the light, it will go back along exactly the same path:

We see then that i = 45 °, r = 28.1 °.

So refractive index = sin 45 ° / sin 28.1 °.





21. In cameras and in magnifying glasses, what kind of images are formed?
  1. Real in camera, real in magnifying glass.
  2. Real in camera, virtual in magnifying glass.
  3. Virtual in camera, real in magnifying glass.
  4. Virtual in camera, virtual in magnifying glass.
In a camera, light spreading out from an object is made to come together again - focused - by the lens onto the film. You can see it on the film with your eyes.

This is a real image.

In a magnifying glass, light spreading out from the object continues to spread out after going through the lens. No image is actually formed anywhere. You cannot see an image unless you look through the glass, where it appears to look bigger.

This is a virtual image.

22. Which of these is used to sterilise medical equipment?
  1. infra-red
  2. microwaves
  3. radiowaves
  4. ultraviolet
From Wikipedia:

"short-wavelength ultraviolet radiation ... is harmful to microorganisms. It is effective in destroying the nucleic acids in these organisms so that their DNA is disrupted by the UV radiation. This removes their reproductive capabilities and kills them."

(http://en.wikipedia.org/wiki/Ultraviolet_germicidal_irradiation)

23. A student hears the thunder 5 s after seeing a flash of lightning, and calculates that the lightning is 1500 m away. What does this assume?
  1. Light is much faster than sound, which travels at 300 m/s.
  2. Light is 300 m/s faster than sound.
  3. Light is 300 times faster than sound.
  4. The thunder is produced 6 s after the lightning.
When lightning strikes, light and sound are produced at the same time.

The light reaches the student first. 5 s later, the sound reaches the student.

The time for light is very much shorter than the time for sound. So the actual time for the sound is very nearly 5 s.

Suppose that it takes sound 5 s to travel the 1500 m.

Then the speed of sound is distance / time = 1500 / 5 = 300 m/s.

24. Which property is important for an electromagnet?
  1. easy to demagnetise, difficult to magnetise
  2. retains magnetic strength, difficult to magnetise
  3. retains magnetic strength, easy to magnetise
  4. easy to demagnetise, easy to magnetise
An electromagnet is usually made by a coil of wire around an iron rod.

An electric current in the coil would magnetise the iron rod.

Ideally, we want to be able to switch on the magnetic field when we need it, and switch it off when we do not.

So the rod should be easy to magnetise, and easy to demagnetise.

25. Two uncharged metal spheres P and Q touch each other.

A positive charge is moved close to P. Q is then moved away. Which of the following is true?
  1. P becomes negative, Q becomes positive, and they have the same amount of charges.
  2. P becomes negative, Q becomes positive, and they have the different amount of charges.
  3. P becomes positive, Q becomes negative, and they have the same amount of charges.
  4. P becomes positive, Q becomes negative, and they have the different amount of charges.
At first, there is zero charge in P and Q.

The positive charge induces negative charge in P and positive charge in Q.

When Q is moved away, the charges stay in P and Q.

There is the same amount in each, since the total is zero.






26. Which of the following will not reduce the resistance of a piece of wire?
  1. Cover it with plastic.
  2. Make it thicker.
  3. Make it shorter.
  4. Make it colder.
If the wire is covered with plastic, electric current still flows in the wire only. So the resistance is not affected.

On the other hand, making the wire thicker, shorter or colder will all reduce the resistance.

27. A 3 V battery is connected to a 2 Ω resistor. What is the current?
  1. 0.67 A
  2. 1.5 A
  3. 10 A
  4. 24 A
The formula is voltage = current x resistance, or V = IR.

To find current, rearrange to make I the subject: I = V/R.

Then I = 3 V / 2 Ω

28. The voltages and currents are measured for a few resistors. Which of the following is for a 100 Ω resistor?
  1. (1 V, 5 mA), (3 V, 30 mA)
  2. (1 V, 10 mA), (3 V, 30 mA)
  3. (1 V, 20 mA), (3 V, 60 mA)
  4. (1 V, 30 mA), (3 V, 60 mA)
The formula is voltage = current x resistance, or V = IR.

To find resistance, rearrange to make R the subject: R = V/I.

Apply this to each set of (voltage, current) values.

Only (b) gives 100 Ω for both sets:

1 V / 10 mA = 1 V / 0.010 A = 100 Ω, and

3 V / 30 mA = 3 V / 0.030 A = 100 Ω

In other options, one or both results are different.

29. Which switch can light the lamp?

  1. 1
  2. 2
  3. 3
  4. 4
Consider all possible paths.

For this path, we must close switches 2, 3 and 4:

For this path, we must close switch 3:

For this path, we must close switches 1 and 3:


30. Which of the following is in joules?
  1. charge
  2. current
  3. energy
  4. power
The units are:

charge - coulomb
current - ampere
energy - joule
power - watt.





31. The insulation of the wire to a kettle is broken. The live wire touches the case, which is earthed. What happens then?
  1. Current keeps flowing to earth.
  2. Fuse melts and current stops.
  3. The case is live.
  4. The case is hot.
Live wire is at 240 V. Earth is at 0 V. When live wire touches the case, current flows.

The current is large because of the big potential difference and very little resistance between wire and case.

The fuse is always placed in series with the live wire. So the large current flows through the fuse.

The fuse gets very hot and melts. This breaks the circuit and current stops.

32. Current flows in four wires as shown:

Which two pairs attract each other?
  1. J and K; K and M.
  2. J and K; L and M.
  3. J and L; K and M.
  4. J and L; L and M.
Currents flowing in the same direction attract.

Currents flowing in opposite directions repel.

33. A simple d.c. motor consists of a square coil in a horizontal magnetic field, and a battery connected to the coil. What is the split-ring commutator for?
  1. Change current direction in coil when coil is horizontal.
  2. Change current direction in coil when coil is vertical.
  3. Change current direction in battery when coil is horizontal.
  4. Change current direction in battery when coil is vertical.
At any one time, one side of the coil feels an upward force from the magnetic field, and the other side feels a downward force.

This causes the coil to rotate.

When one side rotates to the other side, if the force is still in the same direction, the coil would rotate back.

To change the force direction, the current direction must change.

The split-ring commutator will change the current direction.

34. When a magnet is moved slowly into a coil of wire, a current is induced in the coil. Then the magnet is pulled back out quickly. The current in the coil
  1. changes direction and becomes smaller.
  2. changes direction and becomes larger.
  3. becomes smaller in the same direction.
  4. becomes larger in the same direction.
The flux from the magnet goes through the coil.

When the magnet moves to the coil, the amount of flux through the coil increases. This change induces a current in the coil.

When the magnet is pulled out, the flux decreases. This is an opposite change in the flux. So it induces a current in the opposite direction.

The magnet is pulled out quickly. So the the flux decreases at a faster rate than it has increased. So the induced current is also larger.

All these are the result of Faraday's law of electromagnetic induction.

35. A cathode ray oscilloscope shows this wave:

when an a.c. generator is connected. The rotation speed of the generator is doubled. What happens to the wave?
  1. The number of peaks doubles, and the amplitude doubles.
  2. The number of peaks doubles, and the amplitude stays the same.
  3. The number of peaks stays the same, and the amplitude doubles.
  4. The number of peaks stays the same, and the amplitude stays the same.
The a.c. generator is made up of a coil rotating in a magnetic field.

This induces an alternating voltage, which causes the wave on the oscilloscope.

So if the voltage amplitude or frequency change, the same happens to the wave.

If the rotation speed of the generator is doubled, the voltage frequency is doubled.

The voltage amplitude is also doubled, because the flux through the coil changes two times faster. (This is due to Faraday's law of electromagnetic induction.)

So the frequency and amplitude of the wave both double.





36. When the capacitor is charged:

what are the directions of the current?
  1. 1, 3
  2. 1, 4
  3. 2, 3
  4. 2, 4
During charge, the current flows from positive pole of the cell to negative pole.


37. In this radioactive decay: 238U → 234Th, what else is produced?
  1. alpha particle
  2. beta particle
  3. alpha and beta particles
  4. gamma rays
238U has 238 nucleons. 234Th has 234 nucleons.

The difference is 4 nucleons. This would be the alpha particle.

38. Which of the following about the atomic nucleus is correct?
  1. Fission gives larger nuclei. Fusion produces energy in a star.
  2. Fission gives larger nuclei. Fusion produces energy in a power station.
  3. Fission gives smaller nuclei. Fusion produces energy in a star.
  4. Fission gives smaller nuclei. Fusion produces energy in a power station.
Fission is the splitting of a nucleus into smaller parts.

Fusion is the joining of nuclei to form a bigger one

39. The count rate of a radioactive sample falls from 1600 to 200 in 3 minutes. What is the half life?
  1. 0.75 minutes
  2. 1 minutes
  3. 3 minutes
  4. 9 minutes
Half of 1600 is 800.
Half of 600 is 400.
Half of 400 is 200.

So there are 3 half lives in 3 minutes.

Therefore half life is 1 minutes.


40. Isotopes are nuclei with
  1. different number of protons, different number of nucleons.
  2. different number of protons, same number of nucleons.
  3. same number of protons, different number of nucleons.
  4. same number of protons, same number of nucleons.
Definition of isotope:

same number of protons, different number of neutrons.

Score = correct, out of 40 questions.

(Remember to check the stopwatch above to see how long you have taken.)

Correct answers: