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Papers 5 and 6 · AO3

Papers 5 and 6: experiments and planning

Core and Extended · Paper 5 or Paper 6 (20%)

🎯What you need to be able to do

  • Carry out (Paper 5) or describe and analyse (Paper 6) the standard experimental contexts in the syllabus.
  • Turn a relationship into a straight-line graph and use its gradient and intercept.
  • Plan an investigation: choose the variable, apparatus, method, controls, table and analysis.
  • Identify hazards and suggest precautions; suggest specific improvements.

📚The contexts

The syllabus lists the contexts you should expect: measuring lengths, volumes, forces, short times and small distances; derived quantities such as extension per unit load, resistance or acceleration; testing the relationship between two variables; comparing angles of reflection or densities; heating and cooling; springs and balances; timing motion or oscillations; electric circuits (connecting them and measuring current and p.d.); optics with pins, mirrors, prisms, lenses and glass blocks; and unfamiliar procedures with simple apparatus. The skills page covers readings, tables and graphs; this page covers the experiments.

Timing oscillations: the pendulum

A pendulum hangs from a clamp; its length l is measured from the pivot to the centre of the bob, and a fiducial mark is placed below the lowest point. A graph of T squared against l is a straight line through the origin through five plotted crosses.
Plotting T2 (not T) against l gives a straight line.
  • Measure l from the pivot to the centre of the bob; keep the swings small (about 10°).
  • Time 20 oscillations, starting and stopping as the bob passes the fiducial mark; repeat and average; T = t / 20.
  • Why: reaction time (~0.2 s) is a large fraction of one period (~1 s) but a small fraction of 20.

Straight-line graphs from circuits

A cell, an ammeter, an unknown resistor X and a resistance box R in series. A graph of 1 over I against R is a straight line with gradient 0.333 per ohm and intercept 1.67; X equals the intercept divided by the gradient, 5.0 ohms.
Rearrange so that the plotted quantities form y = mx + c; the unknown then comes from the gradient and intercept.

Paper 5 and Paper 6 often give an equation and ask you to plot an unfamiliar combination (1/V, 1/I, T2…) against a variable. Write the equation in the form y = mx + c, identify what the gradient and intercept represent, then read them from your line. Connect ammeters in series and voltmeters in parallel; open the switch between readings so wires do not heat up (their resistance would change).

Optics: pins and a mirror or block

On paper on a pin board, a plane mirror stands on a line. Pins P1 and P2 mark a ray towards the mirror at an angle to the normal; P3 and P4 are placed in line with the images of P1 and P2 seen in the mirror. The rays are drawn and the angles measured.
Pins well apart (at least 5 cm) make the ray direction more accurate.

The same method traces a ray through a rectangular or semicircular glass block, or a prism: mark the outline, place two pins on the incident ray, sight two more through the block, and join up. A converging lens’s focal length can be estimated by focusing a distant window on a screen.

Heating and cooling

Three cups of hot water with thermometers: one with no insulation and no lid, one wrapped in cotton wool, and one wrapped with a lid. Each starts with the same volume of water at the same temperature, and the temperature is read every 30 s for 5 minutes.
Change one thing at a time: here, the insulation.
  • Control: the volume of water, the starting temperature, the room (draughts), the cup type, the time between readings.
  • Compare the temperature fall in the same time or plot cooling curves on the same axes.
  • Hazard: hot water can scald — stand to pour, keep cups away from the bench edge, wipe up spills.

Other contexts to know

springs: measure lengths against a vertical ruler with a set square; extension = new length − original length (topic 1c)
density: two methods (measuring and displacement), then compare using the 10% rule (topic 1b)
moments: balance a metre rule on a pivot with loads at measured distances (topic 1c)
specific heat capacity: heater, thermometer, energy from IVt or a joulemeter (topic 2b)
resistance of a wire: V and I for different lengths of constantan wire, R = V/I against length (topic 4b)

📝The planning question

The last question usually asks you to plan an experiment you do not carry out. Marks go to these points — use them as headings:

  1. Variable: state the one independent variable you will change (in words, not just implied by the method).
  2. Apparatus: name what you need in addition to what is given — always a way to measure the dependent variable (e.g. a stop-watch) and the independent variable.
  3. Method: what you do and what you measure, and that you repeat for a new value of the variable.
  4. Control variables: name at least one (two for full marks) that could affect the result.
  5. Table: columns for the independent and dependent variables, each headed quantity / unit.
  6. Conclusion: how you will use the readings — plot a graph of y against x, or compare values to see whether and how y changes.
  7. Extra: at least five values; repeat each measurement and average.

✏️Worked example

A student lets a marble roll from rest down a ramp and times it between two marks drawn on the ramp. Plan an experiment to investigate how one variable affects the time t between the marks. You are given a ramp, a set of marbles and a metre rule. [7] (Modelled on the planning question, 0625/52 and 0625/62 June 2026 Q4.)

Variable: the height of the top of the ramp (the angle of the slope).

Extra apparatus: a stop-watch; blocks to raise the ramp (the metre rule measures the height).

Method: set the ramp height, measure it with the metre rule; release the marble from rest at the same starting line each time; measure the time t between the two marks; repeat three times and average; change the height and repeat for at least five heights (e.g. 5, 10, 15, 20, 25 cm).

Controls: the same marble (mass and size); the same distance between the marks; the same starting point; the same ramp surface.

Table: height h / cm | t1 / s | t2 / s | t3 / s | mean t / s.

Conclusion: plot a graph of mean t against h and describe how t changes as h increases.

Check it. Every one of the seven headings above has at least one sentence. A method without “repeat for a new value”, or a table without units, loses a mark each.
Controlling the variable you are changing. If the height is the independent variable, do not list “same height” as a control.

📝Practise

In the style of Paper 5 and Paper 6.

1. (Practical.) A student measures the density of a cube of modelling clay by (1) measuring its sides and its mass, and (2) displacement in a measuring cylinder. State one technique that improves each method. [2] (Modelled on 0625/52 and 0625/62 June 2026 Q1.)
(1) Measure each side at several places and average (or use a set square so the ruler is straight against the edge). (2) Lower the clay gently on a thread so no water splashes out; read the bottom of the meniscus at eye level; use a measuring cylinder with small divisions.
2. (Practical.) In the circuit above, a student plots 1/I against R and finds a gradient of 0.25 A−1 per Ω and an intercept of 2.0 A−1. Calculate the resistance X and the e.m.f. E. [3] (Modelled on 0625/52 and 0625/62 June 2026 Q3.)
G = 1/E, so E = 1 / 0.25 = 4.0 V. c = X/E, so X = c / G = 2.0 / 0.25 = 8.0 Ω.
3. (Practical.) Explain why the switch should be opened between readings in an electrical experiment. [1]
So the wires and components do not heat up; a change in temperature changes their resistance.
4. (Practical.) A student times 1 oscillation of a pendulum as 1.3 s. Suggest two improvements. [2]
Time 20 oscillations and divide by 20; repeat and take a mean; use a fiducial mark at the centre of the swing to start and stop the timing.
5. (Practical.) Plan an experiment to investigate how the length of a constantan wire affects its resistance. Include the apparatus, method, a control variable and how you would present the results. [6]
Apparatus: power supply, ammeter, voltmeter, switch, constantan wire on a metre rule, crocodile clips. Method: connect the wire in series with the ammeter; connect the voltmeter across the wire between the clips; set a length (e.g. 20.0 cm), close the switch, read V and I, open the switch; repeat for at least five lengths up to 100 cm; R = V/I. Control: the same wire (diameter and material); a small current so the temperature stays constant. Table: length / cm, V / V, I / A, R / Ω. Plot R against length: a straight line through the origin shows R is proportional to length.
6. (Practical.) Why are optics pins placed at least 5 cm apart when marking a ray? [1]
The direction of the line through them is then more accurate (a small error in positioning a pin causes a smaller error in the angle).

🔗Go deeper — other people’s work

These are external resources, not mine. If one stops working, tell me and everything above it on this page still stands.

  • Institute of Physics — practical physics experiment guides
  • Cambridge International — the 0625 syllabus list of apparatus for the practical papers