Question

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

• A. $\frac{1}{4}$amp
• B. 4 amp
• C. $\frac{1}{2}$amp
• D. 2 amp

Answer 1

Answer: (A)

$\frac{1}{4}$amp

Answer 2

$P = \frac{V^{2}}{R} \Rightarrow 100 = \frac{(200)^{2}}{R}$ ⇒ $R = \frac{4 \times 10^{4}}{10^{2}} = 400\Omega$

Now, $i = \frac{V}{R} = \frac{100}{400} = \frac{1}{4}amp$