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.

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., 4 × 10 - 3 W m - 2, 5 × 10 - 3 W m - 2, 6 × 10 - 3 W m - 2, 7 × 10 - 3 W m - 2

MARKS App · Accepted Answer

Total power = 100 W Visible radiation power = 5% of total power = 5 1 0 0 × 1 0 0 = 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 = Power Area = 5 4 × 3 · 1 4 1 0 2 = 4 × 1 0 - 3 W m - 2

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