Read it level, measure from l₀. Extension is the total stretch.
Stretching a spring is one of the most common Paper 6 questions. You hang loads on a spring, read its length on a vertical metre rule, work out the extension e = l − l0, plot a graph, find the spring constant k and then use the spring to find an unknown mass. Watch the set-up built step by step, with the variables and the graphs beside it, then build it yourself and check it against the mark points.
Past-paper referenceOriginal experiment, wording and figures, written in the style of Cambridge IGCSE Physics 0625 Paper 6 (Alternative to Practical). It is not copied from a past paper. The “what the examiners said” notes are our paraphrase of the Principal Examiner Reports for Teachers.
Practise next: 0625/62 February/March 2025, (measuring the length of a spring, l against m, and the mass of an unknown object) · official past papers
Practise next: 0625/62 May/June 2023, (l₀, extensions, table headings and a graph of L against e) · official past papers
Practise next: 0625/61 May/June 2024, (a technique for l₀, L against e and the spring constant from the gradient) · official past papers
Practise next: 0625/62 May/June 2024, (spring constant from oscillations and from a graph) · official past papers
Examiner reports used: 0625 March 2025, June 2023 and June 2024 (Papers 61 and 62), with the November 2024 Paper 43 report on the spring practical.
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What a full-mark diagram shows
The set-up
A spring hanging from a clamp stand, with slotted masses on a hanger, and a metre rule clamped upright close to the spring.
Reading the length
A pointer (or a set square held horizontally) at the bottom of the coils, the rule checked vertical with a set square, and the scale read at eye level.
The table
Headings L / N, l / cm and e / cm; lengths to 0.1 cm; e = l − l0, the total extension every time.
The graph
Neat crosses, a thin best-fit line not forced through the origin, a large triangle for the gradient, and clear lines to read off an unknown value.
Habits the examiner reports keep asking for
Say how, not just what: “use a set square” is too vague. Say where it goes and what it checks.
Extension is always from l0, not the increase since the previous load.
Record lengths to 0.1 cm with the unit: 10.0 cm, not 10 cm.
A best-fit line balances the points; it does not just join the first and last points, and it is not forced through the origin.
To time oscillations more accurately, time more of them (then divide), and use T = t / 20, not 20 / t.