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Date November 2019 Marks available 2 Reference code 19N.3.SL.TZ0.2
Level Standard level Paper Paper 3 Time zone 0 - no time zone
Command term Estimate Question number 2 Adapted from N/A

Question

The resistance R of a wire of length L can be measured using the circuit shown.

In one experiment the wire has a uniform diameter of d = 0.500 mm. The graph shows data obtained for the variation of R with L.

The gradient of the line of best fit is 6.30 Ω m–1.

Estimate the resistivity of the material of the wire. Give your answer to an appropriate number of significant figures.

[2]
a(i).

Explain, by reference to the power dissipated in the wire, the advantage of the fixed resistor connected in series with the wire for the measurement of R.

[3]
a(ii).

The experiment is repeated using a wire made of the same material but of a larger diameter than the wire in part (a). On the axes in part (a), draw the graph for this second experiment.

[2]
b.

Markscheme

evidence of use of ρ = given gradient × wire area
OR
substitution of values from a single data point with wire area ✔

ρ=«=6.30×π×0.500×10-322=»1.24×10-6«Ω  m»

NOTE: Check POT is correct.
MP2 must be correct to exactly 3 s.f.

a(i).

measurement should be performed at a constant temperature
OR
resistance of wire changes with temperature ✔

series resistance prevents the wire from overheating
OR
reduces power dissipated in the wire ✔

by reducing voltage across/current through the wire ✔

a(ii).

ANY straight line going through the origin if extrapolated ✔
ANY straight line below existing line with smaller gradient ✔

b.

Examiners report

[N/A]
a(i).
[N/A]
a(ii).
[N/A]
b.

Syllabus sections

Core » Topic 1: Measurements and uncertainties » 1.1 – Measurements in physics
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Core » Topic 1: Measurements and uncertainties
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