A-LevelPhysicsPhysical quantities and units9702/23 · May/June 2018 · Q18 Marks

Answer all the questions in the spaces provided. (a) An analogue voltmeter is used to take measurements of a constant potential difference across a resistor. For these measurements, describe one example of

(a)(i)a systematic error,[1]
(a)(ii)a random error.[1]
(b)The potential difference across a resistor is measured as 5.0V ± 0.1 V. The resistor is labelled as having a resistance of 125 Ω ± 3%.
(b)(i)Calculate the power dissipated by the resistor. power = ........................................................................................... W[2]
(b)(ii)Calculate the percentage uncertainty in the calculated power. percentage uncertainty = .............................................................. %[2]
(b)(iii)Determine the value of the power, with its absolute uncertainty, to an appropriate number of significant figures. power = ........................................................................................... W[2]

Mark scheme

Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.

[B1] zero error or wrongly calibrated scale
[B1] reading scale from different angles or wrongly interpolating between scale readings/divisions
[C1] P=V²/R or P=VI and V=IR
[A1] P = 5.0²/125 or 5.0×0.04 or (0.04)² × 125 = 0.20 W
[C1] %V=2% or ∆V/V = 0.02
[A1] %P = (2 × 2%) + 3% or %P = (2 × 0.02 + 0.03) × 100 = 7%
[C1] absolute uncertainty in P = (7 / 100) × 0.20 = 0.014
[A1] power = 0.20 ± 0.01 W or (2.0 ±0.1) × 10⁻¹ W

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