Question

A bulb has a resistance of 20 Ω and the p.d. across its terminals is V. If the bulb is used for t seconds, then the energy consumed by the bulb is:

Options

• $$\frac{V}{20} \times t$$

• $$\frac{V^2}{20} \times t$$

• $$V \times t \times 20$$

• $$\frac{V \times t^2}{20}$$

Answer 1

$$\frac{V^2}{20} \times t$$

Explanation:

Electrical energy is $$W = \frac{V^2}{R}t$$. Substituting $$R = 20,\Omega$$ gives the correct expression. The other options do not follow from the energy formula.