Question

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

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

Answer 1

Answer: (C)

Since, power rating of bulb in both the countries India and USA should be same, so
$\frac{V_1^2}{R_1}=\frac{V_2^2}{R_2}$
$\Rightarrow \frac{220\times 220}{R_1}=\frac{110\times 110}{R_2}$
$\Rightarrow \frac{R_2}{R_1}=\frac{110\times 110}{220\times 220}$
$\Rightarrow R_2=\frac{R}{4}\left(\because R_1=R\right)$