The work function of aluminium is  $4.2eV.$ If two photons, each of energy $3.5 eV$strike an electron of aluminium, then emission of electrons will be

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:

A $100 \;W$ sodium lamp radiates energy uniformly in all directions. The lamp is located at the centre of a large sphere that absorbs all the sodium light which is incident on it. The wavelength of the sodium light is $589\; nm$.

$(a)$ What is the energy per photon associated with the sodium light?

$(b)$ At what rate are the photons delivered to the sphere?

Dual nature of radiation is shown by

Assertion : The phtoelectrons produced by a monochromatic light beam incident on a metal surface have a spread in their kinetic energies.
Reason : The work function of the metal is its characteristics property.