Which consumed the least amount of energy?

Which consumed the least amount of energy?

• A. a 5-watt LED bulb used for 24 hours
• B. a 20-watt incandescent bulb used for 12 hours
• C. a 40-watt fluorescent lamp used for 10 hours
• D. a 60-watt electric fan used for 6 hours

Answer: (A)

Energy consumption equals power times time. Multiply each device’s power by how long it runs: the 5-watt LED bulb for 24 hours uses 5 × 24 = 120 watt-hours (0.12 kWh), the 20-watt incandescent for 12 hours uses 20 × 12 = 240 Wh, the 40-watt fluorescent for 10 hours uses 40 × 10 = 400 Wh, and the 60-watt fan for 6 hours uses 60 × 6 = 360 Wh. The smallest amount is 120 Wh, so the 5-watt LED bulb used for 24 hours consumes the least energy.

Energy consumption equals power times time. Multiply each device’s power by how long it runs: the 5-watt LED bulb for 24 hours uses 5 × 24 = 120 watt-hours (0.12 kWh), the 20-watt incandescent for 12 hours uses 20 × 12 = 240 Wh, the 40-watt fluorescent for 10 hours uses 40 × 10 = 400 Wh, and the 60-watt fan for 6 hours uses 60 × 6 = 360 Wh. The smallest amount is 120 Wh, so the 5-watt LED bulb used for 24 hours consumes the least energy.