First slide

Electrical power

Question

An electric bulb rated for 500 watts at 100 volts is used in a circuit having a 200 volt supply. The resistance R that must be put in series with the bulb so that the bulb draws 500 W is

Moderate

A

$10 Ω$
B

$20 Ω$
C

$50 Ω$
D

$100 Ω$

Solution

Rated current through the circuit, $i = \frac{500}{100} = 5 A$
Potential difference across $R, 100 = 5 \times R \Rightarrow R = 20 Ω$

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