Physics Paper 2 Mistakes

A child drops a ball.

The ball hits the ground and bounces.

Figure 1 shows the velocity-time graph for the ball from when the ball is dropped until when the ball reaches the top of its first bounce.

Air resistance has been ignored.

Describe the motion of the ball between points A and B on Figure 1. [2 marks]

Uniform acceleration

A child drops a ball.

The ball hits the ground and bounces.

Figure 1 shows the velocity-time graph for the ball from when the ball is dropped until when the ball reaches the top of its first bounce.

Air resistance has been ignored.

What direction is the ball moving between points C and D on Figure 1? [1 mark]

Up

A child drops a ball.

The ball hits the ground and bounces.

Figure 1 shows the velocity-time graph for the ball from when the ball is dropped until when the ball reaches the top of its first bounce.

Air resistance has been ignored.

When the ball hits the ground, energy is transferred from the ball to the Earth.

Explain how the data in Figure 1 shows this energy transfer. [4 marks]

• Velocity just after bounce < velocity just before bounce

  • ball has lost energy

• Loss of E_k + reduced max E_p after bounce

• Total energy of ball and Earth constant

A student carried out an investigation to determine the spring constant of a spring.

Table 1 gives the data obtained by the student.

Force in N	Extension in cm
0	0.0
2	3.5
4	8.0
6	12.5
8	16.0
10	20.0

Describe a method the student could have used to obtain the data given in Table 1. [6 marks]

Your answer should include any cause of inaccuracy in the data.

Your answer may include a labelled diagram.

• Set up apparatus as shown in diagram

• Record length of unstretched spring u/ metre ruler

• Hang 2N weight on bottom of spring

• Record new length of spring

• calculate extension

• Repeat steps 3 – 5:

  • add another 2N weight each time until 10N

• Sources of inaccuracy:

  • not clamping ruler vertical

  • not fixing ruler u/ clamp

  • parallax error

A student carried out an investigation to determine the spring constant of a spring.

Table 1 gives the data obtained by the student.

Force in N	Extension in cm
0	0.0
2	3.5
4	8.0
6	12.5
8	16.0
10	20.0

The student measured the extension for five different forces rather than just measuring the extension for one force.

Suggest why. [1 mark]

Reduce effect of random error

Seismometers on the Earth’s surface record the vibrations caused by seismic waves.

Figure 3 shows the vibration recorded by a seismometer for one P-wave.

Calculate the frequency of the P-wave shown in Figure 3. [1 mark]

0.4 Hz

Label this diagram of a wave.

1. Peak

2. Trough

3. Amplitude

4. Wavelength

Describe what the amplitude of a wave is.

• Maximum displacement of point on wave

• Away from undisturbed position

Describe what the wavelength of a wave is.

Distance from a point on one wave to equivalent point on adjacent wave

Describe what the frequency of a wave is.

No. of waves passing a point each sec

What is the equation for the time period of a wave?

$period=\frac{1}{frequency}$ $T=\frac{1}{f}$

• period — seconds (s)

• frequency — hertz (Hz)

Define wave speed.

Speed at which energy is transferred (or wave moves) through medium

What is the equation for wave speed?

wave speed = frequency × wavelength

$v=f\lambda$

• wave speed — metres per second (m/s)

• frequency — hertz (Hz)

• wavelength — metres (m)

Fill in this table:

Transition	Velocity (v)	Frequency (f)	Wavelength (λ)
Less Dense to Denser (e.g. Air to Solid)	__________	___________	____________
Denser to Less Dense (e.g. Solid to Air)	__________	__________	_____________

1. Increases

2. Decreases

3. Constant

4. Constant

5. Increases

6. Decreases

Explain why the study of seismic waves provides evidence for the structure of the Earth’s core. [2 marks]

• S-waves cannot travel through liquid

• S-waves don’t travel through outer core

Describe how ultrasound waves can be used for medical and industrial imaging.

• US waves frequency > than upper limit of human hearing

• US waves partially reflected at boundary b/ two diff media

• Time taken for reflections to reach detector can be used to determine how far away boundary is

Describe seismic waves.

• Produced by earthquakes

• P-waves and S-waves

  • provide evidence for structure and size of Earth’s core

Describe P-waves and S-waves.

• P-waves — longitudinal

  • travels at diff speeds in solids + liquids

• S-waves — transverse

  • cannot travel through liquid

Describe what echo sounding is.

• Uses high frequency sound waves

  • detects objects in deep water + measure water depth

Figure 4 shows a simple seismometer made by a student.

To test that the seismometer works, the student pushes the bar magnet into the coil and then releases the bar magnet.

Why does the movement of the bar magnet induce a potential difference across the coil? [1 mark]

MF around coil changes

Figure 4 shows a simple seismometer made by a student.

To test that the seismometer works, the student pushes the bar magnet into the coil and then releases the bar magnet.

The seismometer cannot detect small vibrations.

Suggest two changes to the design of the seismometer that would make it more sensitive to small vibrations. [2 marks]

• Stronger MF

• More turns on coil

The further a swimmer dives below the surface of the sea, the greater the pressure on the swimmer.

Explain why. [2 marks]

• Increasing depth = increasing height above swimmer

  • increases force of water acting on swimmer

Figure 7 shows the apparatus a student used to investigate the reflection of light by a plane mirror.

The student drew four ray diagrams for each angle of incidence.

The student measured the angle of reflection from each diagram.

Table 2 gives the student’s results.

	Angle of reflection
Angle of incidence	Test 1	Test 2	Test 3	Test 4
20	19	22	20	19
30	31	28	32	30
40	42	40	43	41
50	56	49	53	46

For each angle of incidence, the angle of reflection has a range of values.

This is caused by an error.

Suggest what the student may have done during the investigation to cause each angle of reflection to have a range of values. [1 mark]

Misjudging centre of ray

Figure 7 shows the apparatus a student used to investigate the reflection of light by a plane mirror.

The student drew four ray diagrams for each angle of incidence.

The student measured the angle of reflection from each diagram.

Table 2 gives the student’s results.

	Angle of reflection
Angle of incidence	Test 1	Test 2	Test 3	Test 4
20	19	22	20	19
30	31	28	32	30
40	42	40	43	41
50	56	49	53	46

The student concluded that for a plane mirror, the angle of incidence is equal to the angle of reflection.

Explain whether you agree with this conclusion. [2 marks]

Use examples from the results in Table 2 in your answer.

• Angle of reflection usually diff to angle of incidence

• At 20°, 30° + 40° – one other measurement that is the same

Figure 7 shows the apparatus a student used to investigate the reflection of light by a plane mirror.

The student drew four ray diagrams for each angle of incidence.

The student measured the angle of reflection from each diagram.

Table 2 gives the student’s results.

	Angle of reflection
Angle of incidence	Test 1	Test 2	Test 3	Test 4
20	19	22	20	19
30	31	28	32	30
40	42	40	43	41
50	56	49	53	46

The student concluded that for a plane mirror, the angle of incidence is equal to the angle of reflection.

What extra evidence could be collected to support the student’s conclusion? [1 mark]

Collect results for 10° and 60°

Figure 7 shows the apparatus a student used to investigate the reflection of light by a plane mirror.

The student drew four ray diagrams for each angle of incidence.

The student measured the angle of reflection from each diagram.

Table 2 gives the student’s results.

	Angle of reflection
Angle of incidence	Test 1	Test 2	Test 3	Test 4
20	19	22	20	19
30	31	28	32	30
40	42	40	43	41
50	56	49	53	46

State one change the student should make to the apparatus if he wants to use the same method to investigate diffuse reflection. [1 mark]

Replace mirror w/ irregular reflecting surface

Figure 10 shows a boat towing a small dinghy.

The tension force in the tow rope causes a horizontal force forwards and a vertical force upwards on the dinghy

• horizontal force forwards = 150 N

• vertical force upwards = 50 N

Draw a vector diagram to determine the magnitude of the tension force in the tow rope and the direction of the force this causes on the dinghy. [4 marks]

• Magnitude of the tension force in the tow rope = ________ N

• Direction of the force on the dinghy caused by the tension force in the tow rope = ____________

• 158 N

• 19° above the horizontal

A student used a simple transformer to investigate how the number of turns on the secondary coil affects the potential difference (p.d.) across the secondary coil.

The student kept the p.d. across the primary coil fixed at 2V.

Figure 12 shows the results collected by the student.

Figure 12 contains one anomalous result.

Suggest one possible reason why this anomalous result occurred. [1 mark]

Too few turns on secondary

A student used a simple transformer to investigate how the number of turns on the secondary coil affects the potential difference (p.d.) across the secondary coil.

The student kept the p.d. across the primary coil fixed at 2V.

Figure 12 shows the results collected by the student.

The transformer changes from being a step-down to a step-up transformer.

How can you tell from Figure 12 that this happens? [1 mark]

p.d. across secondary goes above 2V

A spot-welder is a device that uses a transformer to produce a large current to join box sheets of metal together.

Figure 13 shows a transformer demonstrating how a large current can heat and join two nails together.

Calculate the current from the power supply needed to provide a power output of 336 W. [5 marks]

Use the data in Figure 13.

The transformer is 100% efficient.

• $P = VI$

  • $$336 = I × 1.75$$

  • $$I = 192$$

• $\frac{V_{p}}{V_{s}}=\frac{n_{p}}{n_{s}}$

  • $$\frac{640}{4}=\frac{V_{p}}{1.75}$$

  • $$V_{p}=280V$$

• $V_{p}I_{p}=V_{s}I_{s}$

  • $$280× I_{p}=1.75×192$$

  • $I_{p}=1.2A$

A satellite is in a circular orbit around the Earth.

Figure 14 shows the velocity of the satellite at two different positions in the orbit.

Explain why the velocity of the satellite changes as it orbits the Earth. [3 marks]

• Gravity causes satellite to accelerate

• Acceleration cause change in direction

• Direction changes → velocity changes

In 1772, an astronomer called J Bode developed an equation to predict the orbital box radii of the planets around the Sun.

Table 3 shows Bode’s predicted orbital radii and the actual orbital radii for the planets that were known in 1772.

Planet	Predicted orbital radius in millions of kilometres	Actual orbital radius in millions of kilometres
Mercury	60	58
Venus	105	108
Earth	150	150
Mars	240	228
Jupiter	780	778
Saturn	1500	1430

J Bode used his equation to predict the existence of a planet with an orbital radius of 2940 million kilometres.

The planet Uranus was discovered in 1781.

Uranus has an orbital radius of 2875 million kilometres.

Explain why the discovery of Uranus was important. [2 marks]

• Supported prediction

• Provides evidence that equation is correct

Light is usually described as a wave.

Light can also be described as a stream box of particles. These are two different scientific models of light.

Why do scientists sometimes have different models like the wave and particle models of light? [1 mark]

Diff models may be appropriate in diff situations

Sometimes an old scientific model is replaced by a new model.

Explain why scientists replace an old scientific model with a new model. [4 marks]

Include an example from Physics in your answer.

• New evidence

• Evidence cannot be explained w/ existing model

• New model explains new evidence

• Nuclear model of atom replaced plum pudding model

Some students used water waves in a ripple tank to model the behaviour of light waves.

Figure 16 shows what happens to the wave fronts as they pass the boundary between deep water and shallower water.

Explain why refraction happens at the boundary between the deep water and shallower water. [3 marks]

• Speed slower in shallow water

• Edge of wave entering shallow water slows down

• Part of wave in deeper water continues at higher speed

Some students used water waves in a ripple tank to model the behaviour of light waves.

Figure 17 shows the wave fronts travelling parallel to the boundary between deep water and shallower water.

Explain why the wave fronts in Figure 17 do not refract at the boundary. [2 marks]

• Every point on wave enters shallow water at same time

• Every point slow down at same time

The circle in Figure 18 represents a straight wire carrying a current. The cross shows box that the current is into the plane of the paper.

Complete Figure 18 to show the magnetic field pattern around the wire. [2 marks]

• three circles w/ clockwise arrows

Figure 19 shows a simple electric motor.

When there is a current in the coil, the coil rotates continuously.

Explain why. [4 marks]

• Sides of coil parallel to magnet experience force

• Forces cause moments – act in same direction

• Every half turn two halves of commutator swap f/ one carbon brush to other

• Each half turn commutator reverses current

Two students investigated the reflection of light by a plane mirror.

Figure 4 shows the different equipment the students used.

Explain two ways that Method A is better than Method B. [4 marks]

• Don’t need to move mirror to measure angles

  • more likely to record correct angle of incidence and reflection

• Ray in method A does not diverge

  • easier to judge centre position of ray

Compressions are areas of high __________ while rarefactions are areas of low _____________.

pressure