Question

Diagram alongside shows graphs for four resistors A, B, C and D for voltage against current.

1. Which resistor is suitable for making a filament of an electric bulb?
2. Give a reason for your answer.

Answer 1

1. Resistor D is suitable for making the filament of an electric bulb.
2. The V–I graph of D is not a straight line; it curves towards the voltage axis. This shows that D's resistance increases as the current increases because the filament heats up. Hence, D is a non-ohmic resistance like the filament of an electric bulb.