If a 40-watt bulb operates for 5 hours, how many kilowatt-hours does it consume?

• A. 0.1 kWh
• B. 0.2 kWh
• C. 0.5 kWh
• D. 1 kWh

Answer: (B)

To determine how many kilowatt-hours a 40-watt bulb consumes when it operates for 5 hours, you start by converting watts to kilowatts. A watt is one-thousandth of a kilowatt, so a 40-watt bulb is equivalent to 0.04 kilowatts.

Next, you multiply the power (in kilowatts) by the time (in hours) to find the energy consumed in kilowatt-hours. The calculation is as follows:

0.04 kW x 5 hours = 0.2 kWh.

This signifies that the bulb consumes 0.2 kilowatt-hours over the duration of five hours. Understanding this calculation is essential in assessing energy consumption for various electrical devices, thereby allowing for better management of energy usage in practical applications.