Question

In a DC motor, the input is measured as 2 kW ± 4% and the losses are 200 ± 5 W.

The percentage limiting error of the output power is 
1. 9%
2. 6.5%
3. 1.5%
4. 4.7%

Answer 1

Correct Answer - Option 4 : 4.7%

Input = 2 kW ± 4%

Error in the input \(= \frac{4}{{100}} \times 2 \times {10^3} = 80\;W\)

Losses = 200 ± 5 W

Output = Input – Loses

= (2000 ± 80) – (200 ± 5)

= 1800 ± 85 W

Limiting error in the measurement of output

Losses \( = \frac{{85}}{{1800}} \times 100 = 4.72\% \)