Question

In India electricity is supplied for domestic use at $220\, V$. It is supplied at $110 \,V$ in USA. If the resistance of a $60 \,W$ bulb for use in India is $R$, the resistance of a $60 \,W$ bulb for use in USA will be

• A. R
• B. 2R
• C. R/4
• D. R/2

Answer 1

Answer: (C)

R/4

Answer 2

In India, $P_I= \frac{(220)^2}{R}$
In USA, $P_U= \frac{(110)^2}{R_U}$
as $P_I=P_U\Rightarrow \frac{(220)^2}{R} = \frac{(110)^2}{R_U}$
$\Rightarrow R_U= \frac{110\times110}{220 \times 220} R = \frac{R}{4}$.