About 5 % of the power of 100 W light bulb is converted to visible radiation. What is the average intensity of visible radiation at a distance of 10 m ? Assume that the radiation is emitted isotropica

Question

About 5 % of the power of 100 W light bulb is converted to visible radiation. What is the average intensity of visible radiation at a distance of 10 m ? Assume that the radiation is emitted isotropically and neglect reflection.

TestHub · Accepted Answer

Total power = 100 W

Visible radiation power = 5% of total power

$= \frac{5}{100} \times 100 = 5 W$

At a distance of 10 m, the energy distributed in the form of sphere Area of sphere = 4π (radius)²

The intensity of visible radiation

$= \frac{Power}{Area}$ $= \frac{5}{4 \times 3 \cdot 14 {(10)}^{2}} = 4 \times 1 0^{- 3} W m^{- 2}$

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