Question

A bulb rated at (100W-200V) is used on a 100 V line. The current in the bulb is

• A. 1/4 amp
• B. 4 amp
• C. 1/2 amp
• D. 2 amp

Answer 1

Answer: (A)

The correct option is A 1/4 amp
Given,

$P=100W$; power of the bulb

$V=200V$; voltage rating

So value of resistance-

$P=\frac{V^2}{R}$

$\Rightarrow R=\frac{V^2}{P}$

$\Rightarrow R=\frac{{200}^2}{100}$

$\Rightarrow R=400\Omega$

Now applied voltage changes to $100V$, so current passing through the resistance-

$I=\frac{V}{R}$

$\Rightarrow I=\frac{100}{400}$

$\Rightarrow I=\frac{1}{4}A$