The resistance of hot tungsten filament is about 10 times the cold resistance. What will be the resistance of 100 W and 200 V lamp when not in use?

Options

A. `400 Omega`
B. `200 Omega`
C. `40 Omega`
D. `20 Omega`

Answer

C

Explanation

(c ) It is given `R_(Hot) = 10 R_(cold)` also resistance at rated
temperature `R = (V^(2))/(P) = (200 xx 200)/(100) = 400 Omega`
So resistance when lamp not in use.
`R_(Cold) = (R_(Hot))/(10) = (400)/(10) = 40 Omega`