The resistance of hot tungsten filament is about 10 times the cold resistance. What will be the resistance of 100W and 220V lamp when not in use?
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When the lamp is in use, it is hot.
Using Joule's Law of heating,
P= V²/ R
R=200²/100. =400Ω when operating
It is given resistance of hot lamp is 10 times the cold lamp.
Hence, R cold=. 400/10
=40Ω
Hope it helps you dear..
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