Question

The radiation pressure exerted by a 450 W light source on a perfectly reflecting surface placed at 2m away from it, is :

• A. $1.5 \times 10^{-4} \text{ Pascals}$
• B. 0
• C. $6 \times 10^{-5} \text{ Pascals}$
• D. $3 \times 10^{-5} \text{ Pascals} $

Hint:

Use the formula for radiation pressure on a perfectly reflecting surface. Remember to calculate the intensity of the light at the given distance.

Answer 1

The Correct Option is C

\( P_{rad} = \frac{2I}{C} \) 

Where I = intensity at surface C = Speed of light \( Power = \frac{450}{Area} = \frac{450}{4\pi r^2} \) 

\( I = \frac{450}{4\pi \times 4} = \frac{450}{16\pi} \) 

\( P_{rad} = \frac{2 \times 450}{16\pi \times 3 \times 10^8} = \frac{150}{8\pi \times 10^8} \) 

\( = 5.97 \times 10^{-8} \approx 6 \times 10^{-8} \) Pascals