The resistance of hot filament of the bulbis about 10 times the cold resistance. What will be the resistance of 100 W-220V lamp,when not in use?
(α) 48 Ω
(b) 400 Ω
(c) 484 Ω (d) 48.4 Ω
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Answer:
When the lamp is in use, it is hot.
Using Joule's Law of heating,
P=
R
V
2
R=
100
200
2
=400Ω when operating
It is given resistance of hot lamp is 10 times the cold lamp.
Hence, R
cold
=
10
400
=40Ω
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