Current Electricity - Result Question 74

79. 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

[2004]

(a) $R / 2$

(b) $R$

(c) $2 R$

(d) $R / 4$

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Answer:

Correct Answer: 79. (d)

Solution:

(d) $P=\frac{V^{2}}{R} \Rightarrow R=\frac{V^{2}}{P}=\frac{(220)^{2}}{60}=\frac{4(110)^{2}}{60}$

$R^{\prime}=\frac{(110)^{2}}{60}=\frac{R}{4}$