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Question -

About 5% of the power of a 100 Wlight bulb is converted to visible radiation. What is the average intensity ofvisible radiation

(a) at a distance of 1 m from thebulb?

(b) at a distance of 10 m?

Assumethat the radiation is emitted isotropically and neglect reflection.



Answer -

Power rating of bulb, P = 100 W

It isgiven that about 5% of its power is converted into visible radiation.

Power of visible radiation,

Hence, the power of visibleradiation is 5W.

(a) Distance of a point from the bulb, d = 1 m

Hence,intensity of radiation at that point is given as:

(b) Distanceof a point from the bulb, d1 = 10 m

Hence,intensity of radiation at that point is given as:

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