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## QuestionPhysicsClass 12

The work function of caesium is $$2.14\mathit{eV.}$$ Find
The wavelength of the incident light if the photo current is brought to zero by a stopping potential of   $$0.06V$$ .

The photo current is brought to zero, this happens when the maximum kinetic energy of photons becomes equal to the potential energy $$v_o$$  by the stopping potential $$v_o$$  i.e.
$$h=6.62\times 10^{-34} \;Js$$
$$e=1.6\times 10^{-19}C$$
$$ev_o=\mathit{hv}-\phi_o=\frac{\mathit{hc}}{\lambda }-\phi_o$$
$$\lambda =\frac{\mathit{hc}}{ev_o+\phi_o}$$
$$=\frac{6.62\times 10^{-34}\times 3\times 10^8}{\left(1.6\times 10^{-19}\times 0.60\right)+\left(2.14\times 1.6\times 10^{-19}\right)}$$
$$=4.54\times 10^{-7}\text{ m }$$