Work function of nickel is 5.01 eV. When ultraviolet radiation of wavelength 200 $\stackrel{\mathrm{o}}{\mathrm{A}}$ is incident on it, electrons are emitted. What will be the maximum velocity of emitted electrons?

$\text{ Energy corresponding to }2000\text{Å}=12375/2000\mathrm{eV}=6.2\mathrm{eV}$

E=W+KE

Maximum kinetic energy is

$\begin{array}{l}(6.2-5.01)\mathrm{eV}=1.19\mathrm{eV}\\ \text{ Now, }\frac{1}{2}\times 9.1\times {10}^{-31}\times v_{max}^2=1.19\times 1.6\times {10}^{-19}\\ \text{ or }{v}_{max}^2=\frac{1.19\times 1.6\times {10}^{-19}\times 2}{9.1\times {10}^{-31}}\\ =0.418\times {10}^{12}=41.8\times {10}^{10}\\ \text{ or }{v}_{max}=6.46\times {10}^5{\mathrm{ms}}^{-1}\end{array}$