Question

An electric bulb is marked 100W, 220V. If the supply voltage drops to 115V, what is the heat energy produced by the bulb in 20 minutes?

Answer 1

The bulb is rated 100 W , 220V. 

The maximum current the bulb can draw is I then,

V*I = 100

220*I = 100

I = 100/220 = 5/11 A

The voltage is 115 V

then, the energy consumed per second is 

=115 I = 115 × 5/11 = 52.28 J/s  (approx) 

If the bulb is lit for 20 min 

Then, the energy consumed is = 52.28 × 20 × 60 =  62736J

so 62736 J amount of  energy is converted into heat and light energy in the 20 min.

Answer 2

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