Define the terms: (i) work function, (ii) threshold frequency and (iii) stopping potential, with reference to photoelectric effect.
Calculate the maximum kinetic energy of electrons emitted from a photosensitive surface of work function 3.2 eV, for the incident radiation of wavelength 300 nm.    

Work function is the minimum amount of energy required to remove an electron to infinity, from the surface of a given metal.

Threshold frequency is the minimum frequency of the incident light which can cause the ejection of electrons without giving them additional energy.

The amount of potential that is required to stop the electron having the maximum kinetic energy from moving is known as stopping potential. 

Numerical.
The maximum kinetic energy of emitted photoelectron is given by
              $\mathrm{K}.\mathrm{E}. = \frac{1}{2}{{\mathrm{mv}}^2}_{\max } = \mathrm{hv}-{\mathrm{\varphi }}_0$

$\Rightarrow$                      $\boxed{\mathrm{E} = \frac{\mathrm{hc}}{\mathrm{\lambda }}-{\mathrm{\varphi }}_0}$
$\Rightarrow$                        $\mathrm{E} = \frac{6.6 \times {10}^{-34}\times 3\times {10}^8}{300 \times {10}^{-9}}-3.2 \times 1.6\times {10}^{-19}$

$$\begin{gathered} = 6.6 \times {10}^{-19}-5.12 \times {10}^{-19} \\ = 1.48 \times {10}^{-19}\mathrm{J}. \end{gathered}$$