Question

The electric motor operates on 200V supply and a current of 15 A. If the efficiency of motor is 40% then resistance of motor winding is

• A. 10 $\Omega$
• B. 8 $\Omega$
• C. 20 $\Omega$
• D. 25 $\Omega$

Answer 1

Answer: (B)

8 $\Omega$

input power $P=VI=200\ast 15=3000$

power dissipated as heat $I^{2}R=225R$

Efficiency=$\frac{\text{output power}}{\text{input power}}$

$\frac{40}{100}=\frac{3000-225R}{3000}$

$\frac{8}{20}=\frac{3000-225R}{3000}$

$24000=60000-4500R4500R=36000R=\frac{36000}{4500}R=8\Omega$