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For a conductor, the current I and the voltage V across it are directly proportional (the V-I graph is a straight line through the origin, i.e. ohmic behaviour). Which type of graph best represents the variation of power P dissipated with the current I?

1. An upward parabola through the origin (P proportional to I²).
2. A straight line through the origin.
3. A horizontal straight line.
4. A rectangular hyperbola.

Correct answer: An upward parabola through the origin (P proportional to I²).

Solution

Since V is proportional to I (constant R), P = VI = I² R, so P versus I is a parabola opening upward.

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