Question

How many red photon (wavelength l) must strike a totally reflecting screen per second at normal incidence, if the exerted force is to be 1N ?

• A. $\frac{\lambda}{h}$
• B. $\frac{2\lambda}{h}$
• C. $\frac{\lambda}{2h}$
• D. Infinity

Answer 1

Answer: (C)

$\frac{\lambda}{2h}$

Answer 2

$\frac{2nh}{\lambda} = 1$ or n = $\frac{\lambda}{2h}$