The diagram shows a graph. For a uniform metallic wire, what could the graph not represent?

Question 17

The diagram shows a graph.

For a uniform metallic wire, what could the graph not represent?

y-axis                          x-axis

A          current                         potential difference

B          resistance                    length

C         resistance                    temperature in °C

D         potential difference     current

Reference: Past Exam Paper – November 2015 Paper 11 Q31

Solution:

Answer: C.

A uniform metallic wire obeys Ohm’s law (V = IR). So, a current-p.d. graph and a p.d.-current graph would be straight line. [A and D incorrect]

Resistance of wire: R = ρL / A

So, a resistance-length graph would also be a straight line. [B incorrect]

A graph of resistance against temperature will not be a straight line as the resistance of the metal wire increases with temperature. The higher the temperature, the greater the increase in temperature. So, the graph would be a curve, not a straight line.