Question

A coil is needed to operate an arc lamp of 150 V, 50 Hz. The lamp of resistance of 5 ohms when running at 10A. Find inductance of the choke coil, if the same arc lamp is to be operated on 160 V, DC. What is the additional resistance required?

• A. 5Ω
• B. 4.5Ω
• C. 5.5Ω
• D. 2.5Ω

Answer 1

The correct option is D 2.5Ω

A choke coil whose voltage= $250V$ (rms)

Frequency= $50Hz$

Resistance= $15\Omega$

Running at= $10A$ (rms)

Inductive choke coil= (Refer to Image)

$10=\frac{250}{\sqrt{{15}^2+x_{L}2}}$

or, $\sqrt{{15}^2+x_L^2}=\frac{250}{10}$

or, $\sqrt{125+X_L^2}=25$

or, $X_L^2=625-225=400$

or, $X_L=20$

Now, $X_L=WL$

or, $20=50\times L\times 2\Pi$

or, $L=\frac{20}{50\times 2\Pi }$

or, $L=\frac{1}{5\Pi }H$ .