Question

A stream of photons impinging normally on a completely absorbing screen in vacuum exerts a pressure P. If I is the irradiance then –

• A. P = $\frac{2I}{c}$
• B. P = Ic
• C. P = $\frac{I}{c}$
• D. P = 2Ic

Answer 1

Answer: (C)

P = $\frac{I}{c}$

Answer 2

Pressure = $\frac{F}{A}$= $\frac{P \times n}{At}$ = $\frac{h}{\lambda}$ × $\frac{n}{At}$

Irradiance = Intensity = I = $\frac{nhc}{\lambda At}$