JEE Main · 2021 · 26 Aug 2021 · Shift 2 · Current Electricity

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An electric bulb of 500 watt at 100 volt is used in a circuit having a 200 V supply. Calculate the resistance R to be connected in series with the bulb so that the power delivered by the bulb is 500 W.

(A) $20Ω$ ✓ Correct
(B) $5Ω$
(C) $10Ω$
(D) $30Ω$

Answer: (A)

Solution

The bulb gives its rated

500

W only when it carries its rated

100

V, and then it draws

I = \frac{P}{V} = \frac{500}{100} = 5 A

The series resistance carries the same current and must take up the rest of the supply voltage,

200 - 100 = 100

V, so

R = \frac{100}{5} = 20 Ω

JEE Main · 2021 · 26 Aug 2021 · Shift 2 · Single correct option

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