Edexcel IGCSEPhysicsGeneral Applications11 Marks

11 A student investigates how the resistance of a wire depends on its length. [Figure 9] shows the circuit the student uses.

(a)Explain why the voltmeter is connected in parallel with the wire.[2]
(b)The student measures the potential difference (p.d.) across the wire and the current through it for different lengths. [Table 5] shows the student's results.[9]

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Mark scheme

Marking points from the official mark scheme. The mark or mark type is shown in brackets.

Question 11(a)
B1 for voltmeter has very high / infinite resistance
B1 for so negligible / no current flows through it / so it does not affect the circuit current
Question 11(b)
M1 for correct calculation of resistance (R=V/I) for at least one data point
C1 for correct calculation of all resistance values in the table
A1 for suitable scales for axes and axes labelled (including units) for a graph of Resistance vs Length
C1 for plotting points accurately and drawing a straight line of best fit through the origin
M1 for calculating the gradient of the line (showing working)
A1 for correct value of gradient (e.g. 0.048-0.052 Ω/cm)
C1 for stating the relationship: resistance is directly proportional to length (as a straight line through the origin)
M1 for linking the gradient to the resistance per unit length / resistivity if cross-sectional area were known
A1 for explanation of why the line should pass through the origin (zero length, zero resistance)

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