Question

A DC motor has an input power of \(5\,\text{kW}\) and total losses of \(1\,\text{kW}\). The efficiency of the motor is

• A. \(75\%\)
• B. \(80\%\)
• C. \(85\%\)
• D. \(90\%\)

Hint:

Efficiency of a machine is \[ \boxed{ \eta= \frac{\text{Output Power}}{\text{Input Power}}\times100\%. } \]

Answer 1

The Correct Option is B

Step 1: Calculate the output power. \[ P_{\text{out}} = P_{\text{in}} - \text{Losses} = 5-1 = 4\,\text{kW}. \]

Step 2: Find the efficiency. \[ \eta = \frac{P_{\text{out}}}{P_{\text{in}}}\times100 = \frac{4}{5}\times100 = 80\%. \] Hence, \[ \boxed{80\%} \] Therefore, \[ \boxed{(B)} \] is the correct answer.