Question

A light of energy flux \[ 9\ \text{W cm}^{-2} \] is incident for \(20\) minutes on a black surface of area \[ 100\ \text{cm}^2. \] Then the maximum average force exerted on the surface is \[ (c=3\times10^8\ \text{m s}^{-1}) \]

• A. \[ 3\times10^{-3}\ \text{N} \]
• B. \[ 3\times10^{-6}\ \text{N} \]
• C. \[ 3\times10^{-8}\ \text{N} \]
• D. \[ 10\ \text{N} \]

Hint:

For a perfectly absorbing surface: \[ P_{\text{rad}}=\frac{I}{c}. \] For a perfectly reflecting surface: \[ P_{\text{rad}}=\frac{2I}{c}. \] Force is obtained from \[ F=P_{\text{rad}}A. \]

Answer 1

The Correct Option is B