IGCSE Physics 0625 Paper 6: Precision, Graphs and the Marks Everyone Loses

Physics Paper 6 is the only paper you sit where you can get the right number and still lose the mark.

Write 1.4 when the column shows 1.40. Head a column Length instead of length / cm. Calculate a gradient from two points that are almost touching. Every one of those is a correct answer that scores zero, and together they account for more lost marks in Alternative to Practical than any genuine physics misunderstanding.

The good news is that Physics Paper 6 recycles a small set of experiments. Pendulums, springs, resistance wires, lenses, cooling curves, density. Once you know the set and you have fixed the precision habits, this becomes the most reliable 40 marks on your timetable.

The six experiments that keep coming back

Cambridge does not have an infinite supply of one-hour experiments that work on paper. Look across five years of 0625 Paper 6 and the same contexts cycle through, lightly re-dressed.

Refraction through a glass block, moments and balancing a metre rule, and specific heat capacity appear regularly too. If you have worked through all of these once, very little in the exam will be genuinely unfamiliar.

The technique that earns the most marks: count many, then divide

If a question asks you to find the period of a pendulum, the answer is never "start the stopwatch, let it swing once, stop the stopwatch."

You time 20 oscillations and divide by 20.

The reason matters, because examiners ask for it. Your reaction time — roughly 0.2 s at each end — is a fixed, absolute error. It does not shrink when the measurement gets shorter. So:

The absolute error is identical. The percentage error collapses. That is the whole argument, and writing it in that form — "the timing error is the same but is a much smaller fraction of a longer time" — is what scores.

Precision: where correct answers score zero

Decimal places follow the instrument, not the number

If you read a ruler to the nearest millimetre, every length in that column has one decimal place in centimetres. A reading that lands exactly on 16 cm is written 16.0, not 16. Dropping the zero implies you measured less precisely than you did, and the mark scheme catches it.

The same applies to a stopwatch reading 12.30 s — the trailing zero is information, not decoration.

Table headings carry the unit, and only there

Cambridge's convention is quantity / unit:

The unit goes in the heading once. It never appears beside individual numbers in the body of the table.

Reading a scale correctly

• Parallax — read at eye level, perpendicular to the scale. On a ruler, the classic fix is "view the scale from directly above the mark."
• Meniscus — read the bottom of the curve for water, at eye level.
• Zero error — check the instrument reads zero before you start. If it does not, subtract the offset from every reading. This is a systematic error and no amount of repeating will remove it.
• The worn ruler end — start measuring from the 1.0 cm mark rather than the end, and subtract. Examiners like this answer.

Graphs: the four marks almost everyone can get

A typical Paper 6 graph question is worth four or five marks, and they are awarded almost mechanically. Get these in order and they are yours.

1. Axes — labelled with quantity and unit
   Same convention as the table: extension / cm. Independent variable on the x-axis. This mark requires no physics at all.
2. Scale — fill at least half the grid
   If your plotted points occupy less than half the printed grid in either direction, you lose the scale mark. Use 1, 2, 5 or 10 units per square. Never 3 or 7 — the arithmetic afterwards becomes a trap.
3. Plotting — small, sharp crosses
   Accurate to within half a small square. Use a fine pencil and a small neat cross or encircled dot, not a blob covering two squares.
4. Best-fit line — one thin line, judged by eye
   Roughly equal numbers of points either side. Do not join the dots. Do not force it through the origin unless the physics requires it. If the question expects a curve, draw a smooth curve, not a series of straight segments.
5. Gradient — a large triangle, drawn on the graph
   Your triangle must span at least half the length of your line. Draw it, label the co-ordinates you used, and show the subtraction. A gradient with no visible triangle usually loses a mark even if the number is right.

Errors and improvements: the two-clause rule

The last part of most Paper 6 questions asks for a source of error, an improvement, or both. This is the biggest mark-loser in the paper, and the fix is a sentence structure.

Name the change, then name the error it removes.

If your improvement is one clause long, it is almost certainly worth nothing. Two clauses, every time.

If you have never done these experiments

Many schools enter students for Paper 6 rather than Paper 5 precisely because they do not have the lab time or equipment. That leaves a real gap: the questions assume you have watched a spring stretch past its limit of proportionality, or seen a ray bend at a glass block.

PapaMarks has free interactive versions of several of these — load a spring and watch the load–extension graph build in real time, measure the density of an irregular solid by displacement, or send a ray through a glass block and watch the refraction angle change. They are quick, and they turn the written descriptions in the exam into something you have actually seen happen.

Common questions

The one-line version

Learn the six recurring experiments as procedures, always count many and divide, keep your decimal places consistent, draw a gradient triangle that spans half the line, and never write a one-clause improvement. None of that is physics knowledge — which is exactly why it is the fastest 20% of your grade to secure.