State the laws of photoelectric effect

Write Einstein photo electric equation. Explain the laws of photoelectric emission on the basis of photoelectric equation.

A $100 \mathrm{W}$ 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 sodium light is $589 \mathrm{nm}$.

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

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

Light of frequency $7.21\times {10}^{14}\mathrm{Hz}$ is incident on a metal surface. Electrons with a maximum speed of $6.0\times {10}^5\mathrm{Hz}$ are ejected from the surface. What is the threshold frequency for photoemission of electrons?

 Given Planck's constant $h=6.6\times {10}^{-34} \mathrm{Js}$.

 The mass of the electron ${\mathrm{m}}_{\mathrm{e}}=9.1\times {10}^{-31 }\mathrm{kg}$.