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Exam questions

Exam question © Edexcel International: London Examinations IGCSE Physics Higher Tier Paper 2H, May 2006

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Question 1 (a) A racing car is moving on a straight and level road. Several forces act on the racing car. The size and

direction of three forces are shown by arrows A, B and C.

(i) Mark with an X the centre of gravity of the racing car. (1 mark)

(ii) Complete the table. Use the letters A, B and C from the diagram to show the forces acting on the car. (2 marks)

Force Letter

force moving the racing car forward

backward force

weight

(iii) What causes most of the backward force acting on the racing car?

____________________________________________________________________ (1 mark)

(b) The racing car is moving forward at 10 m/s. The graph shows its velocity for the next 20 seconds.


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(i) What feature of the graph shows that the racing car is accelerating?

____________________________________________________________________ (1 mark)

(ii) Use the graph to calculate the distance travelled in metres in these 20 seconds.

____________________________________________________________________

____________________________________________________________________

Distance travelled = ____________ m (2 marks)

Total (7 marks)


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Answers

Mark scheme

(a) (i) The centre of the X should be at the top of the vertical line that shows force C, within the thick line that surrounds the 'IGCSE' logo.

If the X is more than 1 mm away from the vertical line, you do not get the mark.

1 mark

(ii) B

A

C

2 marks if all correct

1 mark if only one correct

(iii) Air resistance (or drag) 1 mark

(b) (i) The slope of the line (you would also be marked correct if you said that the line was going up).

1 mark

(ii) 500 2 marks

(1 mark if you got the answer wrong but you showed that you knew the distance was represented by the area under the graph, or you wrote down the equation s = ut + ½at2

Examiner feedback

(a) (i) Many students either did not answer this question, or put the X too far from the line of force C.

Remember – although all parts of an object have weight, when we think about the object as a whole, it acts as if all its weight is at the centre of gravity.

The diagram in the question shows the forces where they act. This is not always the case with force diagrams, but you can see that in this case each wheel has an upward force, and the force between the back tyre and the road is shown where the tyre touches the road.

So in this case, the arrow showing the weight of the car (arrow C) has been drawn from the centre of gravity of the car, so the X should be at the top of this arrow.

(ii) Most students got this correct.

(iii) Most students got this correct.

(b) (i) Many students just wrote that the car speeds, or that it accelerates. The question asks ‘what feature of the graph shows that the racing car is accelerating?’, so you need to refer to the graph in your answer.

Some answers just mentioned a straight line, without mentioning the slope. A ‘straight line’ could mean a horizontal line, which would not show acceleration, so mentioning the slope of the line was the key point in answering this part of the question.


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(ii) The distance the car has travelled can be calculated from the area under the graph. Many students got this wrong because they calculated the triangular part of the area (300 m), but they forgot to include the rectangle at the bottom (200 m).

Exam questions


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Question 2 (a) The diagram shows a lorry. It is travelling in a straight line and it is accelerating. The total forward

force on the lorry is F and the total backward force is B.

(i) Explain which is larger, force F or force B.

____________________________________________________________________ (1 mark)

(ii) State an equation which relates acceleration, mass and unbalanced force.

____________________________________________________________________ (1 mark)

(iii) An unbalanced force of 15 000 N acts on the lorry. The mass of the lorry is 12 500 kg. Calculate the lorry’s acceleration and give the unit.

____________________________________________________________________

____________________________________________________________________

Acceleration = ____________ (3 marks)

(b) Another lorry is travelling at a steady speed. Explain how this lorry can be accelerating even though its speed stays the same.

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________ (3 marks)

(c) The thinking distance is the distance which a vehicle travels in the driver’s reaction time. The braking distance is the distance which a vehicle travels when the brakes are on.

(i) State one factor which increases the thinking distance.

____________________________________________________________________

____________________________________________________________________ (1 mark)


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(ii) State one factor which increases the braking distance.

____________________________________________________________________

____________________________________________________________________ (1 mark)

Total (10 marks)


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Answers

Mark scheme

(a) (i) F is larger because the lorry is accelerating. 1 mark – you need the explanation as well to get the mark

(ii) force = mass × acceleration (or F = ma, or any correct rearrangement of the equation).

1 mark

(iii) 1.2 2 marks for the correct number (1 mark if you showed correct working but got the final answer wrong)

m/s2 or m s–2 or N/kg 1 mark

(b) Its direction changes (or it goes round a bend)

Any two of these points: because acceleration is a change of velocity; and velocity is a speed in a particular direction; acceleration (or velocity) is a vector (or not a scalar).

1 mark

2 marks (1 for each point)

(c) (i) The driver has consumed alcohol (has been drinking)/has taken drugs/is tired/is inexperienced/is elderly/is travelling at high speed.

(Answers such as poor weather/bad eyesight/lack of concentration do not count, as these only affect the time before the driver sees the hazard, not the thinking time).

1 mark

(ii) Poor brakes/slippery road/worn tyres/high speed. 1 mark

Examiner feedback

(a) (i) Most students got this correct, but be careful to say that force F is bigger than force B because the lorry is accelerating, not just ‘moving forwards’.

(ii) If the question just asks you to ‘state an equation’, it doesn’t matter which form of the equation you write down. In this case, any of F = ma, m = F/a or a = F/m would have been correct.

You may have memorised this equation using a formula triangle. It is best to write out the equation in full in an exam. If you just draw the triangle, you may not be awarded the mark.

(iii) Always show your working in questions that involve calculations. If you make a mistake and get the final answer wrong, you will still get a mark if the first part of your working was correct.

(b) Some students answered this by saying that it is not possible for an object to accelerate without changing speed. Examiners are not out to trick you – so if the question says ‘explain how this lorry can be accelerating’ the answer is not likely to be ‘it isn’t’! The key thing here was to remember that acceleration is a vector quantity.

It is also helpful to look at the number of marks available. If there are 3 marks available (as in this question), then your answer needs to include three different points.

(c) (i) The question is about thinking distances, so answers that would affect the point at which the driver could see a hazard (such as poor visibility) do not affect the time the driver spends thinking about when to stop.

(ii) Some students answered this part of the question by writing ‘brakes’ or ‘speed’. Neither of these answers would have gained the mark, as ‘speed’ could be high or low, and ‘brakes’ could be good brakes or poor brakes. Saying ‘high speed’ or ‘poor brakes’ would have gained the mark.

Exam questions


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Question 3 (a) State the principle of moments.

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________ (2 marks)

(b) The diagram shows a weighing device called a steelyard.

The weight of the shoulder balances the weight of the arm. The weight of the rider is 8.0 N and this balances the weight of the load when x = 0.12 and y = 0.60 m.

Calculate the weight of the load in newtons.

_______________________________________________________________________

_______________________________________________________________________

Weight of load = ____________ N (2 marks)

Total (4 marks)


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Answers

Mark scheme

(a) When an object is in equilibrium (or balanced), the total clockwise moment = the total anticlockwise moment

1 mark 1 mark

(b) 40 2 marks (1 mark if you showed correct working but got the final answer wrong)

Examiner feedback

(a) Most students got 1 mark for saying that the total clockwise moments were equal to the total anticlockwise moments, but did not get the second for saying that this applied when the object was in equilibrium.

It is worth looking at the number of marks available for a question. In this case there were two marks available, so you know you should be writing down two points in your answer.

(b) Always show your working in questions that involve calculations. If you make a mistake and get the final answer wrong, you will still get a mark if the first part of your working was correct.

In this case, you would have gained 1 mark if you had written something like

load × 0.12 = 8 × 0.60

even if you had not worked out the load correctly.

Exam questions


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Question 4 (a) A teacher connects a 1.5 V cell to an ammeter and a thin metal plate as shown.

The ammeter shows a reading. The teacher tells the class that the charge carriers in the circuit are electrons. He leaves the circuit connected for ten seconds. A student touches the plate and it feels warm.

(i) Draw an arrow on the plate to show the direction of flow of the electrons. (1 mark)

(ii) Explain your answer.

____________________________________________________________________

____________________________________________________________________ (2 marks)

(b) Voltage is energy transferred per unit charge passed.

State the relationship between the volt, the joule and the coulomb.

_______________________________________________________________________

_______________________________________________________________________ (1 mark)

(c) The teacher replaces the metal plate with a glass slide of the same shape. He connects the circuit again for ten seconds. The ammeter reading is too low to read.

Explain why the glass slide does not get warm.

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________ (3 marks)

Total (7 marks)


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Mark scheme

(a) (i) Arrow from positive to negative. 1 mark

(ii) Electrons are negatively charged;

so they flow from negative to positive (or they are attracted to positive, or they are repelled by negative).

1 mark

1 mark

(b) The volt is a joule per coulomb (or you could have written joule = coulomb × volt)

1 mark

(c) It has a larger resistance/it is not a conductor/it has no free electrons;

so there is less/no current;

so less/no power/energy is transferred.

1 mark

1 mark

1 mark

Examiner feedback

(a) (i) Many students got this wrong. The key thing here is to remember that electrons have a negative charge.

Thinking about the direction of an electric current can be confusing sometimes, because when we are thinking about motors or electromagnetic effects, we talk about a ‘conventional current’, which we say flows from positive to negative. This convention was decided on before scientists discovered that current is a flow of electrons.

Read the question carefully; if it asks which way ‘electrons’ are flowing, the answer is from the negative terminal to the positive one. If the question asks which way ‘the current’ flows, the answer would be from positive to negative.

(ii) There are 2 marks here, so you need to have two things in your answer to gain full marks.

(b) Many students mixed up units and quantities when answering this question. Remember that energy, charge and voltage are all quantities (things you can measure). Joules, coulombs and volts are the units you use when you measure those quantities.

(c) Many students scored 2 marks for saying that glass is an insulator so there will be no current through it, but did not gain the third mark by going on to say that this meant that no energy would be transferred.

Often examiners try to help you by giving hints in earlier parts of the question. In this case, part (b) mentioned energy transfer.

Again, look at the number of marks available. If you have said ‘glass is an insulator’, that is 1 mark. If you then say that this means no current will flow, that is your second mark. You need to say something else to get the third mark.

Exam questions

Exam question © Edexcel International: London Examinations IGCSE Physics Higher Tier Paper 2H, November 2007

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Question 5 A circuit contains a resistor R, a thermistor and a buzzer connected to a cell, as shown. The circuit can be used as a simple fire alarm.

(a) (i) Complete the sentence.

When the temperature increases, the resistance of a thermistor ____________.

(1 mark)

(ii) What happens to the current in the circuit when the temperature increases?

____________________________________________________________________ (1 mark)

(b) (i) State the equation which relates voltage, current and resistance.

____________________________________________________________________ (1 mark)

(ii) When temperature increases, does the voltage across R stay the same, increase or decrease?

____________________________________________________________________ (1 mark)

(iii) Explain your answer.

____________________________________________________________________

____________________________________________________________________ (2 marks)

(c) The buzzer starts to sound when the voltage across R is a particular value. Add a voltmeter to the circuit diagram to show how this voltage is measured.

(1 mark)

Total (7 marks)


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Mark scheme

(a) (i) decreases 1 mark

(ii) increases 1 mark

(b) (i) V = I × R (or voltage = current × resistance) 1 mark

(ii) increases 1 mark

(iii) The current in the circuit has gone up;

but its resistance has stayed the same.

1 mark;

1 mark

(c) The voltmeter should be shown connected in parallel across the buzzer, or across resistor R.

1 mark

Examiner feedback

(a) (i) Most students got this right.

(ii) Getting the answer correct depends on you getting the answer to part (i) worked out correctly.

So if you weren't sure if your answer to part (i) was correct, it is still worth trying later parts of the question!

(b) (i) Most students got this right.

You may have memorised this equation using a formula triangle. It is best to write out the equation in full in an exam. If you just draw the triangle, you may not be awarded the mark.

(ii) Some students did not read the question carefully enough, and answered as if they were thinking about the voltage across the thermistor, not the voltage across resistor R.

(iii) This question has 2 marks, so your answer needs to include two different ideas.

Exam questions


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Question 6 A student has two tubes. She puts a ticking watch at the end of tube 1. She points tube 1 towards a hard, flat surface. Then she puts a finger in one ear. She holds the second tube to her other ear and points this tube at the hard, flat surface.

The diagram shows five positions, A, B, C, D and E, for the second tube.

(a) (i) In which position do the ticks sound loudest?

Position ____________. (1 mark)

(ii) Explain your answer by adding lines to the diagram to show the direction of the sound waves.

(2 marks)

(b) Complete the sentences.

When sound waves arrive at the hard, flat surface they are ____________. (1 mark)

The angle of ____________ equals the angle of ____________. (1 mark)

(c) Suggest and explain one reason why the student puts a finger in one ear.

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________ (2 marks)

Total (7 marks)


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Mark scheme

(a) (i) E 1 mark

(ii) Your line should be drawn from the watch through tube 1, reflect from the surface and then go through tube E.

Your lines should include arrows to show that the sound is travelling from the watch to the surface, and then through tube E.

1 mark

1 mark

(b) Reflected.

Incidence, reflection (you can have the words in either order).

1 mark

1 mark (you need both words for the mark)

(c) To block out other sounds;

which could distract/confuse her.

OR

To block the sound coming directly from the watch;

which would be louder than the sound coming through the tube.

1 mark

1 mark

1 mark

1mark

Examiner feedback

(a) (i) The key to getting this right is to remember that sound waves reflect from surfaces just like light waves, with the angle of incidence equal to the angle of reflection.

(ii) Not many students answered this part of the question well. Many drew lines from the surface through more than one tube, or forgot to put arrows on their lines to show the direction in which the sound was travelling. If you are asked to draw lines to show the path of a wave, whether it is light or sound, remember to include arrows to show the direction in which it is moving. In this question, one of the 2 marks for part (ii) was for drawing the arrows correctly.

(c) A lot of students lost marks on this one, too. You will probably have done more experiments with light than with sound, but remember that experiments with light rays are usually done in a darkened room to make it easier to see the light rays you are interested in. Putting a finger in one ear is similar to this – it lets you concentrate on the sound you are experimenting with.

Exam questions


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Question 7 (a) The diagram shows a ray of light entering a glass block.

Calculate the refractive index of the glass.

_______________________________________________________________________

_______________________________________________________________________

Refractive index = ______________________.

Name this shape: ______________________. (2 marks)

(b) (i) Diamond has a refractive index of 2.4. A ray of light enters a diamond at an angle of incidence 36º. Would it change direction more than, the same as or less than the ray entering the glass block?

____________________________________________________________________ (1 mark)


____________________________________________________________________

____________________________________________________________________ (1 mark)

(c) A teacher produces a list of the apparatus required to determine the refractive index of glass. One item is shown. Add three more items.

(3 marks)

Total (7 marks)

Glass block


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Mark scheme

(a) n = sin i / sin r

sin 36° / sin 23° = 1.50

1 mark

1 mark

(b) (i) more 1 mark

(ii) n (refractive index) is greater, so the angle of refraction is smaller for the same angle of incidence

OR

the light slows down more, so the angle of refraction will be less than 23°).

1 mark

(c) Any three things from this list:

• raybox (or pins)

• paper

• board

• protractor

• rule

• set square

• pencil/pen.

3 marks (one for each item)

Commentary

(a) The most common mistake in this question was forgetting the sines.

(b) (i) Not many students answered this correctly. Remember that the larger the refractive index, the more bending occurs at the boundary.

(ii)

(c) Your answer to this part of the question will depend on how you investigated refraction in lessons. You can use a ray box to trace what happens to a ray of light passing through a glass block, or there is an alternative method using pins. Some students wrote pins and a raybox, but only got 1 mark for these two objects, because you do not normally use both in the same investigation.

Some students put vague replies such as ‘torch’ or ‘light’. Responses like these did not gain a mark. You need to be specific – give the correct name for a piece of apparatus.

Exam questions


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Question 8 (a) The diagram shows what happens when water waves pass close to the edge of a piece of plastic.

Name the wave behaviour shown.

_______________________________________________________________________ (1 mark)

(b) (i) The diagram below shows water waves about to pass through a gap. One wavefront is shown after it has passed through the gap.

On the diagram, draw two more wavefronts that have passed through the gap. (3 marks)

(ii) State two changes which would make the wavefronts become more curved after passing through the gap.

1. _______________________________________________________________

2. _______________________________________________________________ (2 marks)

(c) (i) Sound waves with a frequency of 25 000 Hz are directed at a gap. Give a reason why they are not heard on the other side of the gap.

____________________________________________________________________ (1 mark)

(ii) Calculate the wavelength in metres of these sound waves.

The speed of sound is 340 m/s.

____________________________________________________________________

____________________________________________________________________

Wavelength = ____________ (3 marks)

Total (10 marks)


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Mark scheme

(a) Diffraction. 1 mark

(b) (i) Two more wavefronts shown;

with the same wavelength (the same distance between them);

with the correct shape:

1 mark

1 mark

1 mark

(ii) Increase wavelength (or decrease frequency);

decrease size of gap.

1 mark

1 mark

(c) (i) They are beyond the audible range (or you could say the frequency is too high, or give the range of human hearing).

1 mark

(ii) v = f × λ (or any other correct form of the equation).

λ = 340/25 000

= 0.0136 m/s

1 mark

1 mark

1 mark


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Examiner feedback

(a) Most students got this right.

(b) (i) Most students got this correct as well.

(ii) Some students mentioned changing the speed of the waves or the depth of the water, which did not get a mark. Changing the depth changes the speed of waves in water, and changing the speed affects the wavelength of the waves. However, it is the size of the wavelength compared with the size of the gap that affects the amount of diffraction.

(c) (i) Most students realised that the sound could not be heard because of its frequency, and that the gap was not relevant.

(ii) Notice that 1 mark is given for writing down the equation, and 1 mark for substituting the values in the equation. If you have written these things down, you still get 2 marks even if you make a mistake in the final calculation. Always show your working.

Exam questions


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Question 9 (a) Geothermal resources may be used to produce electricity. One advantage is that geothermal

resources are renewable. Describe two other advantages and two disadvantages.

Advantages:

1. __________________________________________________________________

2. __________________________________________________________________

Disadvantages:

1. __________________________________________________________________

2. __________________________________________________________________ (4 marks)

(b) The diagram shows a heat exchanger in a geothermal power station.

On the dotted lines write A, B, C or D where:

A is the hot geothermal water in

B is the geothermal water out

C is the liquid in from the condenser

D is the vapour out to the turbine.

(2 marks)

(c) The data show how the temperature varies with depth where the ground is suitable for geothermal electricity production.

Temperature (°C) 25 40 63 100 155 245

Depth (m) 0 200 400 600 800 1000

(i) Plot a graph of temperature (y-axis) against depth (x-axis).


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(ii) Draw a smooth curve through your points.

(5 marks)

(iii) Geothermal electricity production is possible using temperatures as low as 85 °C.

Use your graph to find the depth in metres where this temperature occurs.

Depth = ____________ m. (1 mark)

Total (12 marks)


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Mark scheme

(a) Advantages – any two from:

• does not take up much space

• does not produce pollution

• does not produce greenhouse gases

• does not depend on the weather.

2 marks, one for each correct point.

Disadvantages – any two from:

• has to be located in a fixed place

• there are not many suitable places

• may bring up hazardous minerals in the water.

2 marks, one for each correct point.

(b) top left: D

upper right: C

bottom left: A

bottom right: B

2 marks (12 mark for

each one correct)

(c) (i) Sensible scales on axes, and plotting the correct variable on each axis.

Axes correctly labelled with quantities and units.

Points plotted correctly to the nearest mm (you lose one mark if one point is more than 1 mm from its correct position, and no marks for this part of (c) (i) if two or more points are more than 1 mm out of place).

1 mark

1 mark

2 marks


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Mark scheme

(ii) Points joined with a smooth curve. 1 mark

(iii) 540 m (any answer between 520 and 560 m would be marked correct). 1 mark

Examiner feedback

(a) Physics exams often have questions asking you to give some advantages and disadvantages of a particular way of generating electricity, and these questions are not usually answered well.

Some students give statements that contradict each other (such as writing down a similar thing as both an advantage and a disadvantage).

Marks are not usually given for any comments about cost (whether saying that a particular resource is cheap or expensive).

(c) (i) You have probably been told to use all the graph paper if you can. But it is more important to have a scale that is easy to read – don’t use an awkward scale just to fill the whole grid.

(ii) Smooth curves are easier to draw if your hand is on the inside of the curve. For this question, it is easier to draw a smooth curve through the points if you turn the paper upside down (or, if you are left-handed, turn it so the top of the question is on your left).

(iii) Be as accurate as you can when reading values from a graph. Draw lines on the graph if it helps you to work out the value, or use a ruler to make sure you are reading along the grid lines correctly.

Exam questions


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Question 10 The diagram shows the inside of a vacuum flask. It may be used to keep soup hot.

(a) Energy transfer can take place by conduction, by convection, and by radiation. Which two of these energy transfers cannot take place through a vacuum?

____________ and ____________ (1 mark)

(b) Explain how the vacuum flask reduces energy transfer by radiation.

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________ (2 marks)

(c) In some vacuum flasks, both the case and the double-walled container are made of metal. These vacuum flasks are stronger. However, they are heavier.

State and explain one disadvantage apart from cost.

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________ (2 marks)

Total (5 marks)


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Mark scheme

(a) Conduction, convection (you can put the answers in either order). 1 mark (you need both to get the mark)

(b) The silvered surfaces;

reflects heat/infrared (or is a poor emitter/absorber of radiation/infrared).

1 mark

1 mark

(c) Any two points from:

• metal is a better heat conductor (or is a poorer heat insulator)

• so the contents will cool/lose heat more quickly

• the casing becomes hot

(you would also get marks if you talked about cold contents gaining heat from the surroundings).

2 marks (1 mark for each point)

Examiner feedback

(a) Most students got this part of the question correct.

(b) Most students got this correct.

(c) Some students gave answers such as ‘weight’ or ‘it might break if you dropped it’. But the question said that these metal vacuum flasks are heavier, so you get no marks for repeating what you have already been told. The question also said they were stronger, so the comment about breaking is not relevant.

Exam questions


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Question 11 (a) A technician uses a hammer to force a nail into a wooden beam.

The hammer has a mass of 0.40 kg. It has a speed of 5.0 m/s just before it hits the nail.

Calculate the kinetic energy of the hammer just before it hits the nail and give its unit.

_______________________________________________________________________

_______________________________________________________________________

Kinetic energy of the hammer = ____________ (3 marks)

(b) The technician raises the hammer to a height of 0.75 m above the beam before bringing it down to hit the nail.

Calculate the increased gravitational potential energy of the hammer at a height of 0.75 m above the beam.

________________________________________________________________________

________________________________________________________________________

Increased gravitational potential energy = ____________ (2 marks)

(c) (i) After raising the hammer to a height of 0.75 m, how much work does the technician do in hitting the nail with the hammer? Give its unit.

____________________________________________________________________

Work done = ____________ (2 marks)


____________________________________________________________________

____________________________________________________________________ (2 marks)

Total (9 marks)


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Mark scheme

(a) 12 × 0.40 × 25 (or give the formula: 1

2 mv2)

= 5

J (or joules)

1 mark

1 mark

1 mark

(b) 0.40 × 10 × 0.75 (or give the formula: mgh)

= 3 J

1 mark

1 mark

(c) (i) 5 – 3 = 2

J

1 mark

1 mark

(ii) Conservation of energy;

means work done = kinetic energy – potential energy.

1 mark

1 mark

Examiner feedback

(a) Most students got this right.

Notice from the mark scheme that you can get a mark for showing the equation or putting the numbers into it, even if you get the final answer wrong, so it is always worth showing your working.

And remember always to give the units for your answers.

(b) Most students got this right.

(c) Many students tried using work = force × distance to calculate this, and so got the wrong answer. If the question is about energy, then it is worth thinking about whether the law of conservation of energy applies. In this question, the kinetic energy of the hammer just before it hits the nail is greater than the gravitational potential energy of the hammer at the top of the swing – so the technician must have added some energy. The difference between the energy at the start (the gravitational potential energy) and the end (the kinetic energy) must be the work done on the hammer.

Exam questions


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Question 12 (a) The kelvin temperature of a fixed mass of gas is not proportional to one of the following quantities.

Place a tick () next to this quantity.

average kinetic energy of its molecules

celsius temperature

pressure at constant volume

(1 mark)

(b) A car handbook recommends that the tyre pressures should be checked. Explain why this should be done when the tyres are cold.

_______________________________________________________________________

_______________________________________________________________________ (2 marks)

(c) The pressure in a tyre at a temperature of 290 K is 200 kPa. Calculate the pressure in kPa in the tyre when the temperature is 310 K.

_______________________________________________________________________

_______________________________________________________________________

Pressure = ____________ kPa (2 marks)

(d) (i) State the relationship between pressure, force and area.

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________ (1 mark)

(ii) A four-wheel car has a weight of 10 000 N. The pressure in each tyre is 200 kPa. Calculate in m2 the area of each tyre which is in contact with the road. Assume the weight of the car is distributed uniformly.

____________________________________________________________________

____________________________________________________________________

Area = ____________ m2 (2 marks)

Total (8 marks)


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(a) Celsius temperature. 1 mark

(b) When tyres heat up;

the pressure increases (or the recommended tyre pressures are for cold air).

1 mark

1 mark

(c) (200 × 310)/290

= 214

(213.8 or 213.79 would also have been marked correct)

1 mark

1 mark

(d) (i) pressure = force/area (or P = F/A, or any correct rearrangement of the formula) 1 mark

(ii) A = F/P = 10 000/200 000 = 0.05

0.05/4 = 0.0125 (m2)

OR

2 marks for working out the weight on each tyre (10 000/4 = 2500), and then dividing this by the pressure (2500/200 000 = 0.0125 m2).

1 mark

1 mark

Examiner feedback

(a) Most students got this one wrong. Y is proportional to X if Y = kX (where k is a constant). For example, pressure = force/area, so for a constant area, pressure is proportional to force.

You can calculate the kelvin temperature by adding 273 to the celsius temperature. The addition of 273 means that the two temperatures are not proportional to one another (the celsius temperature does go up if the kelvin temperature goes up, but it does not double if the kelvin temperature doubles).

(b) For this part of the question, you need to think about what would happen if you checked the pressure when the tyres were hot. If you weren't sure, part (c) of the question may have given you a clue.

(c) Most students answered this one correctly.

(d) (i) Most students answered this correctly.

You may have memorised this equation using a formula triangle. In an exam, it is always best to write out the equation in full, as you may not get the mark if you just draw the triangle.

(ii) Most students lost marks on this question by forgetting to convert kPa to Pa before doing the calculation, or by forgetting that the car has four wheels!

Exam questions

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Question 13 (a) (i) A student takes a balloon to a swimming pool. The balloon is filled with air at a pressure of

120 kPa. The volume of the balloon is 0.025 m3. He takes the balloon to the bottom of the pool. The pressure inside the balloon increases by 20 kPa.

Calculate the new volume of the balloon.

____________________________________________________________________

____________________________________________________________________

New volume = ____________ m3

(2 marks)

(ii) State two assumptions you have made in your calculation.

1. __________________________________________________________________

2. __________________________________________________________________

(2 marks)

(b) (i) Define density.

____________________________________________________________________

(1 mark)

(ii) Did the density of the air in the balloon decrease, stay the same or increase when the student took the balloon to the bottom of the pool?

____________________________________________________________________

(1 mark)

(iii) Explain your answer.

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

(2 marks)

Total (8 marks)

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Mark scheme

(a) (i) 120 × 0.025 = 140 × V

V = 0.0214

(0.021 would have also been marked correct)

1 mark

1 mark

(ii) The mass of air in the balloon is fixed (or the number of molecules stays the same);

the temperature does not change.

1 mark

1 mark

(b) (i) mass/volume 1 mark

(ii) increased 1 mark

(iii) The mass is the same;

but the volume has decreased.

1 mark

1 mark

Examiner feedback

(a) (i) A lot of students tried using the wrong formula to work out the answer to this one, and so gained no marks. If you look at what you are given in the question, you have two different pressures and a volume, and you are asked to calculate a volume. The formula you know that links these variables is p1 × V1 = p2 × V2.

Many students also used 20 kPa as the second pressure, instead of adding this to 120 kPa (the question told you that the pressure increased by 20 kPa).

(ii) Equations for the gas laws show the relationships between two variables, but they all assume that the other things that could vary are kept the same. In this case, the equation p1 × V1 = p2 × V2 works only if the mass of gas and its temperature stay the same.

(b) (i) Some students put weight instead of mass, or put area instead of volume.

(iii) If you remember that density depends on mass and on volume, you should be able to say something about the mass (it stays the same) and volume (it decreases) – for 1 mark each.

Exam questions


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Question 14 (a) A teacher sets up the apparatus shown. A copper wire carrying a current is placed between the poles

of two bar magnets. This wire dips into a small tray of mercury.

The teacher sets up the apparatus in a fume cupboard because mercury vapour is poisonous.

Draw arrows on the diagram to show the direction of:

(i) the current in the copper wire and label it I (1 mark)

(ii) the magnetic field between the poles and label it M (1 mark)

(iii) the resulting force on the copper wire and label it F. (1 mark)

(b) At first the copper wire does not move.

State two changes that could be made to increase the force acting on the copper wire.

1. __________________________________________________________________

2. __________________________________________________________________ (2 marks)

(c) Give two reasons why mercury is used in this demonstration.

1. __________________________________________________________________

2. __________________________________________________________________ (2 marks)

Total (7 marks)


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Mark scheme

(a) (i) Downwards arrow on the copper wire, labelled I. 1 mark

(ii) Arrow from N to S on the magnets, labelled M. 1 mark

(iii) Arrow from copper wire pointing away from the support, labelled F. 1 mark

(b) Increase the current (any of the following would also have been marked correct: reduce the resistance, increase the voltage/power supply, use a thicker wire, use shorter connecting wires);

move the magnets closer together (or use stronger magnets, or a stronger field).

1 mark

1 mark

(c) Any two from:

• it is a liquid at room temperature

• it is metallic

• it is a conductor

• to allow the end of the wire to move

• it is non-magnetic.

2 marks (one for each point)

Examiner feedback

(a) (i) You need to remember the difference between ‘conventional current’ and the flow of electrons. In the days before electrons were discovered, scientists agreed to talk about the current flowing from the positive terminal of a cell or battery towards the negative terminal. This ‘conventional current’ is the current we talk about when we are thinking about electricity and magnetism.

(ii) Many students showed two conflicting directions for the magnetic field. When two poles of a magnet are close to each other like this, all the field lines go from the North pole of one magnet to the South pole of the other.

(iii) You needed to use Fleming’s left-hand rule to work out which way the copper wire would move. Even if you can’t remember the rule, you should be able to remember that the three things (current, field and force) are all at right angles to each other – then you have a 50 per cent change of getting the direction correct!

(b) Most students got this part of the question correct.

(c) Most students got this part of the question correct.

Exam questions


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Question 15 (a) The diagram shows a flat circular coil carrying a current. On the diagram, sketch the magnetic field

pattern of the coil. Use arrows to show the direction of the magnetic field lines.

(3 marks)

(b) When there is a current in the coils, the electromagnet shown below is able to carry small loads from a hook. When the current is switched off the hook and load fall off.

(i) Name a suitable material for the core and the hook.

____________________________________________________________________ (1 mark)

(ii) Explain why this material is suitable.

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________ (2 marks)

Total (6 marks)


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Mark scheme

(a) correct shape for the lines;

in the correct direction;

at least three lines drawn:

1 mark

1 mark

1 mark

(b) (i) Iron. 1 mark

(ii) Any two from:

• it is a soft magnetic material

• it is easy to magnetise

• it is easy to demagnetise.

2 marks (one for each point)

Examiner feedback

(a) You can use your right hand to work out the direction of the magnetic field of a coil. If you curl your fingers up so they are pointing in the direction in which current flows around the coil, your thumb will be pointing towards the north end of the coil.

(b) The important property of iron for use in electromagnets is that it is a ‘soft’ magnetic material, which means it is easy to magnetise, but it also loses its magnetism very easily when the current is switched off.

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Question 16 The diagram shows a transformer. It has a core made of laminated iron and a coil of insulated wire on each side. This transformer has 30 turns on the coil on side A. It has 10 turns on side B.

(a) How would it be used as a step-up transformer?

____________________________________________________________________

____________________________________________________________________ (1 mark)

(b) Why is the wire insulated?

____________________________________________________________________

____________________________________________________________________ (1 mark)

(c) The transformer is used as a step-up transformer. The input is an alternating voltage of 4 V. Calculate the output voltage in volts.

____________________________________________________________________

____________________________________________________________________

Output = ____________V (2 marks)

(d) Complete the sentence.

In a transformer, an alternating input voltage drives an alternating current in the input coil. This produces a ____________ ____________ ____________ in the core. (1 mark)

Total (5 marks)


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Mark scheme

(a) Connect the input to side B (or connect the output to side A). 1 mark

(b) To stop the electricity going through the iron core. 1 mark

(c) 12 V (1 mark if you show the equation but get the final answer wrong). 2 mark

(d) Alternating magnetic field. 1 mark

Examiner feedback

(a) Remember that if you want to increase the voltage (a step-up transformer), the input should be connected to the side with the smallest number of coils.

(b) Some students thought the insulation on the wires was to prevent electric shocks, or to provide heat insulation. The insulation on the wires is to stop electricity flowing straight through the core from the input to the output connections.

(c) Remember to show your working. There are 2 marks for this part of the question, so if you write down the correct equation but make a mistake in calculating your answer, you will still get 1 mark.

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Question 17 A scientist measured the activity of a radioactive isotope. The table shows her results.

Time (hours) Activity (megabecquerels)

0 64 000

1 45 000

2 32 000

3 23 000

4 16 000

(a) (i) Plot these results on the grid and draw a curve of best fit.

(3 marks)

(ii) Calculate the half-life in hours of this radioactive isotope.

Half-life = ____________ hours (1 mark)

(b) The scientist measured the activity in megabecquerels. How many becquerels (Bq) are there in a megabecquerel (MBq)?

1 MBq = ____________ Bq (1 mark)

Total (5 marks)


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Mark schemes

(a) (i) All points correctly shown (points not correct if the ‘blobs’ are bigger than 2 mm, or are more than 1 mm from the correct position);

curve of best fit drawn:

2 marks

1 mark

(ii) 2 1 mark

(b) 1 000 000 (or million, or 106) 1 mark

Commentary

(a) (i) It is easier to draw a smooth curve if your hand is on the inside of the curve – so turn the paper round. And if you are asked for a ‘curve of best fit’ don’t use a ruler to join the points.

Don’t make the ‘blobs’ for your points too big, or you may lose marks.

(ii) In many questions like this, you need to read numbers from the graph you have just plotted. But in this case you can use numbers from the table – as the first reading is 64 000 and there is a number exactly half of this also in the table (32 000). Using numbers from the table (if you can) avoids the possibility of making a mistake reading numbers from the graph.

(b) Many students got this one wrong, thinking that 1 MBq = 1000 Bq. Remember that ‘kilo’ means 1000 (as in kilogram, kilometre) and ‘mega’ means million, or 1 000 000.

Exam questions


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Question 18 (a) Uranium-234 is radioactive. It emits alpha particles and decays to thorium-230. Complete the nuclear

equation for this decay.

(2 marks)

(b) Geiger and Marsden studied the structure of atoms. The diagram shows part of the equipment which they used.

(i) The block of lead helped to shield the scientists from radiation. What was its other purpose?

____________________________________________________________________

____________________________________________________________________ (1 mark)

(ii) Most of the alpha particles went straight through the gold foil. What explanation did the scientists suggest for this?

____________________________________________________________________

____________________________________________________________________ (1 mark)

(iii) Some of the alpha particles were deflected. What explanation did the scientists suggest for the deflection?

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________ (2 marks)


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(iv) Only a small proportion of the alpha particles deflected through a large angle. What explanation did the scientists suggest for the proportion being small?

____________________________________________________________________

____________________________________________________________________ (1 mark)

(v) Some alpha particles were deflected less than others. What two reasons did the scientists suggest for this?

1. _______________________________________________________________

_______________________________________________________________

2. _______________________________________________________________

_______________________________________________________________ (2 marks)

(vi) The alpha particles were detected when they hit a zinc sulfide screen. How did the scientists know that an alpha particle had hit the screen?

____________________________________________________________________

____________________________________________________________________ (1 mark)

Total (10 marks)


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Mark scheme

(a) 230 and 90 for thorium;

4 and 2 for helium

1 mark

1 mark

(b) (i) To produce a narrow beam in one direction. 1 mark

(ii) Most of the gold atom is empty space. 1 mark

(iii) They are repelled by the nucleus of the atom;

as both have a positive charge.

1 mark

1 mark

(iv) The nucleus is very small. 1 mark

(v) They were further away from the nucleus;

they were moving faster.

(You can have the answers in either order.)

1 mark

1 mark

(vi) It made a tiny flash of light/scintillation. 1 mark

Examiner feedback

(a) Most students got this equation correct.

(b) (i) Some students said the other purpose of the lead block was to make all the alpha particles go towards the gold foil. Don’t forget that the lead absorbs alpha particles – it does not reflect them. Reflection would be the only way a shaped block of lead like this could send all the alpha particles towards the foil.

(ii) It was not enough here just to say ‘there is space in the gold’, you had to point out that most of the gold atom is empty space.

(iii) Remember that the alpha particles do not collide with the nucleus – they are deflected from their path by electrostatic forces.

(iv) It was not good enough here just to say the nucleus was ‘small’ – you had to say it was very small.

(v) Remember that the force between two charges gets less if they are further apart, which is why particles further from the nucleus are deflected by a smaller angle.

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