First slide

Electrical power

Question

Two electric bulbs have tungsten filament of same length. If one of them gives 60 watts and other 100 watts, then

Moderate

A

100 watt bulb has thicker filament
B

60 watt bulb has thicker filament
C

both filaments are of same thickness
D

it is impossible to get different wattage unless the lengths are different

Solution

$R \propto \frac{1}{P}$
Hence resistance of 60 watt bulb will be more than resistance of 100 watt bulb
Further R $= ρ (\frac{1}{{πr}^{2}}) or R \propto \frac{1}{r^{2}}$
So, the radius of 100 watt bulb will be more than 60 watt bulb. Hence 100 watt bulb has thicker filament

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