Average force exerted on a non-reflecting surface at normal incidence is $2.4 \times 10^{-4} \mathrm{~N}$. If $360 \mathrm{~W} / \mathrm{cm}^2$ is the light energy flux during span of $1$ hour $30$ minutes. Then the area of the surface is:

Two monochromatic beams $A$ and $B$ of equal intensity $I$, hit a screen. The number of photons hitting the screen by beam $A $ is twice that by beam $ B$. Then what inference can you make about their frequencies ? 

Which of the following is incorrect statement regarding photon

When an inert gas is filled in the place vacuum in a photo cell, then

A monochromatic beam of light of wavelength $400\,nm$ incident normally upon a photosensitive surface ($25\%$ reflects and rest absorbs), produces a pressure of $5 \times 10^{-7}\,Nm^{-2}$ on it. If $0.1\%$ of the incident photons produce electrons then corresponding saturation current will be…………..$\mu A$ (consider area of photosensitive surface $= 5\,cm^2$)