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Home » 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
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
CBSE | Class 10 | Electricity | NCERT | Physics
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

(d) 25 W

Step 1: Using the above ratings, determine the bulb’s resistance.

Bulb rating: P=100W, V=220V

Power, P=\frac{V^{2}}{R}
\Rightarrow \mathrm{R}=\frac{\mathrm{V}^{2}}{\mathrm{P}}=\frac{220 \times 220}{100}=484 \Omega

Step 2: The amount of energy used by the bulb
V ′ =110V is now the voltage drop across the bulb.
As a result, the bulb’s power consumption will be:

\mathrm{P}_{\mathrm{b}}=\frac{\mathrm{V}^{\prime 2}}{\mathrm{R}}=\frac{110 \times 110}{484}

P=25W

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