What is the resistance of the filament of a bulb rated at (100 W – 250 V)? What is the current through it when connected to 250 V line? What will be power if it is connected to a 200 V line?

Solution

Power of the bulb, $P = VI = \frac{V^{2}}{R}$
Resistance across the bulb is then,
$R = \frac{V^{2}}{P} = \frac{250 \times 250}{100} = 625 Ω$

The current flowing through the lamp
$I = \frac{P}{V} = \frac{100 W}{250 V} = 0.8 A$
Now,
Power of the lamp when it is connected to a 200 V line is
$P = \frac{V^{2}}{R} = \frac{200 \times 200}{625} = 64 W$

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Current Electricity

What is the resistance of the filament of a bulb rated at (100 W – 250 V)? What is the current through it when connected to 250 V line? What will be power if it is connected to a 200 V line?

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