Chapter 3: Electricity

Q&A -Ask Doubts and Get Answers

Q
Electricity

Question:

An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed will be –

(a) 100 W      (b) 75 W       (c) 50 W       (d) 25 W

Answer:

P = VI

P = frac{V^2}{R} -----(1)

The resistance of the electric bulb remains constant, so we will first find the resistance of the bulb to find the power consumed by the bulb at 110 W.

Given:

P = 100 W

V = 220 V

Using relation (1), we get

R = frac{V^2}{P}

R = frac{(220)^2}{100}

R = frac{220 	imes 220}{100}

R = 22 	imes 22

R = 484 Omega ---------(2)

Now, when the bulb is operated at 110 V, the electric power consumed by the bulb is given as

P = frac{V^2}{R}

R = 484 Omega {From (2)}

V = 110 V {Given}

P = frac{(110)^2}{484}

P = frac{110 	imes 110}{484}

P = 25 W

So, the correct option is (d).


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