Question

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

(1) \(1.5 \times 10^{-8}\) Pascals

(2) 0

(3) \(6 \times 10^{-8}\) Pascals

(4) \(3 \times 10^{-8}\) Pascals

Answer 1

Correct option is : (3) \(6 \times 10^{-8}\) Pascals

\(P_{rad} = \frac{21}{C}\)

Where \(I = \) intensity at surface

\(C = \) Speed of light

\(I = \frac{Power}{Area} = \frac{450}{4 \pi r^2}\)

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

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

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