Question

A single phase 150 V electric motor absorbs 8.0 A while running at 1500 rev/min and developing 2.8 N-m of torque. The phase angle between voltage and current is \(60^\circ\). What is power efficiency of the motor?

• A. 53%
• B. 63%
• C. 73%
• D. 83%

Hint:

To make calculations faster during exams, use the approximation \(\pi \approx \frac{22}{7}\):
\[ \omega = \frac{2 \times \frac{22}{7} \times 1500}{60} = \frac{1100}{7} \text{ rad/s} \] \[ P_{\text{out}} = 2.8 \times \frac{1100}{7} = 0.4 \times 1100 = 440 \text{ W} \] \[ \text{Efficiency} = \frac{440}{600} \approx 73.33% \] This simple approximation avoids complex decimal division.

Answer 1

The Correct Option is C