A 12 volt electric motor has 1,000 watts input and 1 HP output. Maintaining the same efficiency, how much input power will a 24 volt, 1 HP electric motor require?

A 12 volt electric motor has 1,000 watts input and 1 HP output. Maintaining the same efficiency, how much input power will a 24 volt, 1 HP electric motor require?

• A. 1,000 watts
• B. 2,000 watts
• C. 746 watts
• D. 1,200 watts

Answer: (A)

Power in and power out are linked by efficiency. If the motor delivers 1 horsepower, that’s about 746 watts of mechanical output. The first motor uses 1,000 watts of electrical input, so its efficiency is 746/1000 ≈ 74.6%. If the second motor keeps the same efficiency and still provides 1 HP, it must also supply about 746 watts of mechanical power, so the electrical input stays around 746 / 0.746 ≈ 1,000 watts. Changing the voltage from 12 V to 24 V doesn’t change the energy required per second to produce that much mechanical power; the motor will draw whatever current is needed to keep the input near 1,000 watts. The other options would imply a different efficiency or a different output, which isn’t given here.

Power in and power out are linked by efficiency. If the motor delivers 1 horsepower, that’s about 746 watts of mechanical output. The first motor uses 1,000 watts of electrical input, so its efficiency is 746/1000 ≈ 74.6%. If the second motor keeps the same efficiency and still provides 1 HP, it must also supply about 746 watts of mechanical power, so the electrical input stays around 746 / 0.746 ≈ 1,000 watts. Changing the voltage from 12 V to 24 V doesn’t change the energy required per second to produce that much mechanical power; the motor will draw whatever current is needed to keep the input near 1,000 watts. The other options would imply a different efficiency or a different output, which isn’t given here.