A 100 W light bulb is able to convert 10% of its power to visible radiation. The average intensity of the visible radiation at a distance of 1 m from the bulb is: 

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  1. 0.08 W/m2
  2. 0.8 W/m2
  3. 10 W
  4. 8 W/m2

Answer (Detailed Solution Below)

Option 2 : 0.8 W/m2
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Detailed Solution

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Given:

Power of the source P=100W

The distance from the source of radiation r=1m

Concept:

The intensity of visible radiation is the quantity of visible light emitted per unit time, per unit area

  • \(I=\frac{P}{4\pi r^2}\)

 

where P is the power of the source, Pi is the power of visible radiation, and r is the distance from the source of radiation.

Explanation:

10% of P=Pi

\(P_i=\frac{10}{100}\times100\)

\(\implies P_i=10\ W\)

Now, \(I=\frac{P}{4\pi r^2}\)

Put all values in above formula, we get,

\(I=\frac{10}{4\times3.14\times(1)^2}\)

\(I=0.796\ W/m^2\)

\(I=0.8\ W/m^2\)

Hence, the correct answer is Option-2-\(I=0.8\ W/m^2\).

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