(a) Define electric resistance and state Ohm’s law.
(b) A metallic conductor kept at constant temperature is subjected to various potential differences and the corresponding currents are measured. Explain qualitatively why a straight-line V–I characteristic passing through the origin is obtained.
(c) Describe how the numerical value of the resistance of the conductor can be obtained from such a V–I graph. What is the physical significance of the slope of the graph?
(d) State two reasons why, at higher temperatures, the graph may deviate from a straight line even for the same conductor.