An electrical bulb is marked $100 W, 220 V$ . The bulb is connected to the supply. What is the resistance of its filament and how much is the current flowing through it? Its the filament resistance of the glowing bulb greater, smaller or the same as compared to its resistance when it is not glowing?

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Solution

Step-1 Given data
Power of bulb $= 100 W$
Voltage of bulb $= 220 V$
Step-2 Finding the resistance and current of the bulb
Resistance of the filament, $R = \frac{V^{2}}{P}$ [Where V is the voltage and P is the power]
$R = \frac{220 \times 220}{100}$
$R = 484 W$
Current of the filament, $I = \frac{V}{R}$
$I = \frac{220}{484}$
$I = 0.45 A$
Hence, the resistance of the bulb is $484 W$ and the current of the bulb is $0.45 A$
Heating the filament of the glowing bulb then its resistance will be greater as compared to the resistance when the bulb is not glowing.

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An electrical bulb is marked 100W,220V. The bulb is connected to the supply. What is the resistance of its filament and how much is the current flowing through it? Its the filament resistance of the glowing bulb greater, smaller or the same as compared to its resistance when it is not glowing?