Chapter 34, Problem 72A

The wattage marked on a lightbulb is not an inherent property of the bulb but depends on the amount of voltage to which it is connected, usually 110 V or 120 V.

a. Calculate the Current through a 40-W bulb connected to 120 V.

b. Calculate the current through the same bulb when it is connected to 60 V.

To determine

To find: The current though 40 W bulb

Explanation of Solution

The current though 40 W bulb is

  $I=\frac{P}{V}=\frac{40\text{W}}{120\text{V}}=0.333\text{A}$

To determine

To find: The current through bulb when connected to 60 V

Explanation of Solution

The current through bulb when connected to 60 V is

  $I=\frac{P}{V}=\frac{40\text{W}}{60\text{V}}=0.667\text{A}$