The work function of a photosensitive material is 4.0 eV . This...

The work function of material is given by \begin{aligned} & \phi=\mathrm{hv} \\ & \phi=\frac{\mathrm{hc}}{\lambda} \end{aligned}$$\text{ ..(i) }\left[\because v=\frac{c}{\lambda}\right]$$ where, $\mathrm{h}=$ Planck's constant $=6.63 \times 10^{-34} \mathrm{~J}-\mathrm{s}\mathrm{c}=$ speed of length $=3 \times 10^8 \mathrm{~ms}^{-1}$ and $\lambda=$ wavelength of light Here, $\phi=4 \mathrm{eV}=4 \times 1.6 \times 10^{-19} \mathrm{~J}$ Substituting the given values in Eq. (i), we get $\Rightarrow \quad 4 \times 1.6 \times 10^{-19}=\frac{6.63 \times 10^{-34} \times 3 \times 10^8}{\lambda}$ or $\quad \lambda=\frac{6.63 \times 10^{-34} \times 3 \times 10^8}{4 \times 1.6 \times 10^{-19}} =3.108 \times 10^{-7} \mathrm{~m} \simeq 310 \mathrm{~nm}$