Question

What is the force exerted by a photon of intensity 1.4 kWm^–2 if it falls on a perfect absorber of radius 2 metre ?

• A. 2.35 × 10^–4 N
• B. 10⁸ N
• C. 8.35 × 10⁴ N
• D. 8.8 × 10^–8 N

Answer 1

Answer: (A)

2.35 × 10^–4 N

Answer 2

$\mathrm { F } _ { \mathrm { ex } } = \frac { \mathrm { P } } { \mathrm { c } } = \frac { \mathrm { IA } } { \mathrm { c } }$

I = 1.4 × 10³ W/m²

A = 4pr² = 4 × 3.14 × (2)² m²

F_ex = 2.35 × 10^–4 N