A motor of 1/5 hp (0.2 hp) with 75% efficiency has an electrical input power of approximately?

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Enhance your understanding of the fundamentals of electricity with the AMT General Exam. Study with multiple-choice questions crafted to improve your knowledge and confidence. Prepare effectively for your success!

Multiple Choice

A motor of 1/5 hp (0.2 hp) with 75% efficiency has an electrical input power of approximately?

Explanation:
Input power is found by dividing the mechanical output by the efficiency. A 1/5 hp motor equals about 0.2 hp, which is 0.2 × 746 ≈ 149 W of mechanical output. With 75% efficiency, the electrical input power must be P_in = P_out / η ≈ 149 W / 0.75 ≈ 199 W. So the approximate electrical input power is 199 W. (The 149 W figure is the output power, 746 W is 1 hp in watts, and 375 W would correspond to a different combination of output and efficiency.)

Input power is found by dividing the mechanical output by the efficiency. A 1/5 hp motor equals about 0.2 hp, which is 0.2 × 746 ≈ 149 W of mechanical output. With 75% efficiency, the electrical input power must be P_in = P_out / η ≈ 149 W / 0.75 ≈ 199 W. So the approximate electrical input power is 199 W. (The 149 W figure is the output power, 746 W is 1 hp in watts, and 375 W would correspond to a different combination of output and efficiency.)

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