Physics (AS & A Level) · May / June 2016 · Paper 51 · Question 2
9702
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The question as text
A student is investigating how the extension of a loaded wire depends on the diameter of the wire. The apparatus is set up as shown in Fig. 2.1. wire load F Fig. 2.1 A load F is applied to the wire and the extension e is measured. The experiment is repeated for wires of the same material and same initial length L but different diameter d. It is suggested that e and d are related by the equation e = 4LF πEd 2 where E is a constant. 1
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2(a)[1]
π 4LF E
2(b)[3]
T1 1 d / 106 m–2 T2 13 or 12.8 9.8 or 9.77 6.9 or 6.93 4.7 or 4.73 3.2 or 3.19 1.9 or 1.93 All values to 2 s.f. or 3 s.f. Allow a mixture of significant figures. Must be values in table. U1 From ± 2 to ± 0.1 Allow more than one significant figure.
2(c)(i)[2]
G1 Six points plotted correctly Must be within half a small square. Do not allow “blobs”.
ECF allowed from table. U2 Error bars in 1 d plotted correctly All error bars to be plotted. Must be accurate to less than half a small square.
2(c)(ii)[2]
G2 Line of best fit If points are plotted correctly then lower end of line should pass between (3.2, 3.0) and (3.6, 3.0) and upper end of line should pass between (11.2, 10.0) and (11.6, 10.0). G3 Worst acceptable straight line. Steepest or shallowest possible line that passes through all the error bars. Line should be clearly labelled or dashed. Examiner judgement on worst acceptable line. Lines must cross. Mark scored only if error bars are plotted.
2(c)(iii)[2]
Gradient of the line of best fit; the triangle used should be at least half the length of the drawn line. (1)
Absolute uncertainty: gradient of line of best fit − gradient of worst acceptable line, or ½(steepest worst line gradient − shallowest worst line gradient). (1)
(Should be about 9 × 10⁻¹⁰.)
2(d)(i)[2]
= π× 4 60.479 gradient gradient LF Do not penalise POT. (Should be about 7 × 1010.) N m–2 or Pa Allow in base units: kg m–1 s–2.
2(d)(ii)[1]
Percentage uncertainty in E: (Δgradient/gradient + 0.01/2.50 + 0.5/19.0) × 100. Must be larger than 3%. (1)
2(e)[2]
e in the range 15.5 × 10⁻³ to 18.0 × 10⁻³ m, given to 2 or 3 s.f. Allow mm. (1)
Absolute uncertainty in e, using percentage uncertainty = (Δgradient/gradient + 0.01/2.50 + 0.5/19.0 + 2 × 0.02/0.23) × 100, or e = gradient/d². (1)
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