Question

The resistance of hot filament of the bulb is about 10 times the cold resistance. What will be the resistance of 100 W-220 V lamp, when not in use?​

Answer 1

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

Answer 2

Answer:

484ohm

Explanation:let hot resistance be R

let cold resistance be r

according to given conditions R=10r

given- power = 100w V=220v

P=vi

100=220×I

I=5/11

according to ohm's law

V=IR

220=5/11×R

R=484ohm

since when the lamp is not in use no current passes thus no resistance is created