Exam technique

Your three papers

As an Extended candidate you take three papers.

• Every question on every paper is compulsory.
• Papers 2 and 4 test both the Core and the Supplement content.
• You may use a calculator in every paper.
• Paper 6 has its own page: Paper 6.

Paper 2: multiple choice

• You have 45 minutes for 40 questions. That is just over 1 minute per question.
• Do not get stuck. Mark a hard question, move on, and come back at the end.
• Answer every question. There is no penalty for a wrong answer.
• Cover the options first. Work out your own answer, then look for it. The wrong options are often the answers you get from common mistakes.
• For a calculation, write your working on the question paper. Then check the unit and the power of ten in each option.
• Read every word. Underline words such as not, least, most and incorrect.
• Cross out options you know are wrong. Then choose between the rest.
• On a graph, check which quantity is on each axis before you read it.

Question: A ferry travels 12 km in 0.50 hours. What is its average speed?

• A 0.042 km/h
• B 6.0 km/h
• C 12 km/h
• D 24 km/h

Weak answer: B

Why it is weak: the student multiplied 12 × 0.50 instead of dividing. Option B was written to catch this mistake.

Full-mark answer: D. speed = distance ÷ time = 12 ÷ 0.50 = 24 km/h

Paper 4: theory

• You have 1 hour 15 minutes for 80 marks. That is just under 1 minute per mark.
• Use the marks as a guide. A 3-mark question usually needs 3 separate points.
• Show every step of a calculation: the equation, the numbers put in, the answer and the unit. Method marks count even if the final answer is wrong.
• Convert units first, for example g to kg, cm to m, minutes to s.
• Round only at the end. Keep the full value in your calculator until then.
• If a later part uses your answer to an earlier part, use your answer, even if you are not sure of it. You can still get the method marks.
• Use the exact physics words: “thermal energy”, not “heat energy”; “weight” is a force, “mass” is not.
• Do not copy out the question. Every line you write should add something new.
• Draw diagrams and graphs with a ruler and a sharp pencil. Label them.

Question (3 marks): A 1500 W kettle is switched on for 2.0 minutes. Calculate the energy it transfers.

Weak answer: 1500 × 2 = 3000

Why it is weak: the time is still in minutes and there is no unit, so the answer is wrong and loses most of the marks. Multiplying power by time is the right method, so it may still earn a method mark. Writing the equation first makes that mark safer.

Full-mark answer:

t = 2.0 × 60 = 120 s

E = Pt = 1500 × 120 = 180 000 J = 1.8 × 10⁵ J

Command words

The command word in a question tells you what kind of answer gets the marks. These are the command words used in this syllabus. The meanings are explained here in our own words. The questions and answers are examples written for this site.

Calculate

What it asks for: work out a number from the values given. Show the equation, the numbers put in, the answer and the unit.

Question (2 marks): A trolley of mass 2.0 kg accelerates at 3.0 m/s². Calculate the resultant force on it.

Weak answer: 6

Why it is weak: no working and no unit.

Full-mark answer: F = ma = 2.0 × 3.0 = 6.0 N

Comment

What it asks for: give your judgement on a statement or a result, and back it up with physics.

Question (2 marks): A heavy ball and a light ball are released together, from rest, at the same height. Air resistance is too small to matter. A student says that the heavy ball falls faster. Comment on the student’s statement.

Weak answer: The student is wrong.

Why it is weak: it gives a judgement but no physics to support it.

Full-mark answer: The student is wrong. With no air resistance, both balls fall with the same acceleration of free fall, g. They speed up at the same rate and land at the same time.

Compare

What it asks for: say how two things are the same or different. Mention both things in each point.

Question (2 marks): Compare the motion of the particles in a solid and in a gas.

Weak answer: Gas particles move.

Why it is weak: it only mentions the gas, and solid particles also move.

Full-mark answer: In a solid, the particles vibrate about fixed positions. In a gas, the particles move freely and randomly in all directions, far apart from each other.

Deduce

What it asks for: reach a conclusion from the information in the question, such as a table or a graph. Point to the information you used.

Question (2 marks): A spring stretches 2.0 cm with a load of 1.0 N, 4.0 cm with 2.0 N and 6.0 cm with 3.0 N. Deduce the relationship between the load and the extension.

Weak answer: When the load goes up, the extension goes up.

Why it is weak: it does not give the exact relationship.

Full-mark answer: The extension is directly proportional to the load. When the load doubles from 1.0 N to 2.0 N, the extension doubles from 2.0 cm to 4.0 cm.

Define

What it asks for: give the exact meaning of a term, in words or as an equation with its symbols named.

Question (1 mark): Define momentum.

Weak answer: How hard something is to stop.

Why it is weak: it is a description, not the definition.

Full-mark answer: Momentum is mass × velocity.

Describe

What it asks for: say what happens or what something is like, step by step. You do not need to give reasons.

Question (2 marks): A ray of light passes from air into a glass block at an angle to the surface. Describe what happens to the ray.

Weak answer: It bends.

Why it is weak: it does not say which way it bends.

Full-mark answer: The ray bends towards the normal as it enters the glass. Inside the block it travels in a straight line.

Determine

What it asks for: find an answer from the information given, often by reading from a graph or doing a calculation.

Question (2 marks): The speed–time graph of a cyclist is a straight line from 2.0 m/s at time 0 to 8.0 m/s at 3.0 s. Determine the acceleration of the cyclist.

Weak answer: 8.0 ÷ 3.0 = 2.7

Why it is weak: it uses the final speed instead of the change in speed, and it has no unit.

Full-mark answer: acceleration = change in speed ÷ time = (8.0 − 2.0) ÷ 3.0 = 2.0 m/s²

Explain

What it asks for: give the reasons why or how something happens. Link each cause to its effect, for example with “because” or “so”.

Question (2 marks): A metal spoon is left in a cup of hot tea. Explain why the handle becomes hot.

Weak answer: Because the tea is hot.

Why it is weak: it does not say how the thermal energy reaches the handle.

Full-mark answer: Metal is a good thermal conductor. Thermal energy is transferred along the spoon by free electrons moving through the metal and by vibrating atoms passing energy to their neighbours.

Give

What it asks for: a short answer, either from the information in the question or from memory.

Question (1 mark): Give one example of a renewable energy resource.

Weak answer: Electricity.

Why it is weak: electricity is a way of transferring energy, not an energy resource.

Full-mark answer: Solar energy.

Identify

What it asks for: name, pick out or recognise something. One clear answer is enough.

Question (1 mark): Identify the type of electromagnetic wave used by a television remote control.

Weak answer: Radio waves or infrared.

Why it is weak: it gives two answers and one is wrong, so it scores nothing.

Full-mark answer: Infrared.

Justify

What it asks for: support an answer or a decision with evidence or a physics reason.

Question (2 marks): A student says a 60 cm copper wire has less resistance than a 30 cm copper wire of the same thickness. Is the student correct? Justify your answer.

Weak answer: No.

Why it is weak: there is no reason.

Full-mark answer: No. Resistance is directly proportional to length. The 60 cm wire is twice as long, so its resistance is twice as large.

Predict

What it asks for: say what you expect to happen, using the information given or a pattern. Usually you do not need to explain unless the question asks.

Question (1 mark): A lamp is lit by a battery. A second, identical lamp is added in series. Predict what happens to the brightness of the first lamp.

Weak answer: It changes.

Why it is weak: it does not say how it changes.

Full-mark answer: The first lamp becomes dimmer.

Sketch

What it asks for: a simple drawing or graph by hand. It must show the main shape and features clearly, with labelled axes, but it does not need exact values.

Question (2 marks): Sketch the current–voltage graph for a filament lamp, for p.d. from 0 upwards.

Weak answer: A straight line through the origin.

Why it is weak: that is the graph for a fixed resistor, not a filament lamp.

Full-mark answer:

The key features: current on the y-axis and p.d. on the x-axis, both labelled. The curve starts at the origin. It gets less steep as the p.d. increases, because the filament gets hotter and its resistance increases.

State

What it asks for: a short, clear answer. No explanation is needed.

Question (1 mark): State the unit of power.

Weak answer: kWh

Why it is weak: the kilowatt-hour is a unit of energy, not power.

Full-mark answer: watt (W)

Suggest

What it asks for: use your physics in a new situation where more than one answer could be right. Give a sensible idea and a reason.

Question (2 marks): A street light on an island is powered by a solar cell and a battery. Suggest why it may not stay lit all night during the rainy season.

Weak answer: Because of the rain.

Why it is weak: it does not link the weather to the energy supply.

Full-mark answer: There is less sunlight on cloudy days. The solar cell transfers less energy to the battery, so the battery may run out before morning.

Significant figures

• Significant figures are the digits that carry meaning, counted from the first digit that is not zero. 0.0450 has 3 significant figures. 2.0 has 2.
• If the question says how many significant figures to give, do that.
• Otherwise, when you multiply or divide measured values, give your final answer to the same number of significant figures as the least precise value you used. If you are unsure, 2 or 3 significant figures is usually right.
• Counted numbers (such as 10 swings) and conversion factors (such as 60 s in a minute) are exact. They do not limit the significant figures.
• Round only at the end. Rounding in the middle of a calculation can change the final answer.
• Write numerical answers as decimals, not fractions.
• Write very large and very small numbers in standard form, for example 3.0 × 10⁸ m/s.
• Cambridge papers use a dot on the line for the decimal point. Numbers of 10 000 and above are printed with a space between each group of three digits.

Question (2 marks): A runner covers 125 m in 9.4 s. Calculate the average speed.

Weak answer: 13.29787234 m/s

Why it is weak: it copies every digit from the calculator. The time, 9.4 s, has only 2 significant figures.

Full-mark answer: speed = distance ÷ time = 125 ÷ 9.4 = 13 m/s (2 significant figures)

Units

• Write the unit with every answer. A number without a unit can lose a mark. A few quantities have no unit, such as refractive index.
• Make the units match before you substitute. For example, power in W and time in s give energy in J.
• Write unit symbols exactly. Capital and small letters mean different things: mA means milliamperes, but MA would mean megaamperes.
• Use Cambridge notation: m/s, m/s², kg/m³, N/kg, J/(kg °C).

Convert before you calculate

Exam-day checklist

• Show every step of your working.
• Write the unit with every answer.
• Convert units before you calculate.
• Round only at the end, to a sensible number of significant figures.
• Use the marks as a guide to how many points to make.
• Answer every multiple-choice question.