Electrons ejected from the surface of a metal, when light of certain frequency is incident on it, are stopped fully by a retarding potential of 3V. photoelectric effect in this metallic surface begins at a frequency $6×10^{14}s^{-1}$. The frequency of the incident light in $s^{-1}$ is [Planck’s constant = $6.4×10^{-34}Js$, charge on the electron = $1.6×10^{-19}C$]

$13.5×10^{14}$

The maximum kinetic energy of emitted photoelectrons

$K_{max}=eV_s=e(3V)=3eV$

Work function, $\phi_0=hv_0=(6.4×10^{-34})(6×10^{14})J$

$=\frac{(6.4×10^{-34})(6×10^{14})}{1.6×10^{-19}}eV=2.4eV$

According to Einstein’s photoelectric equation

$hv=K_{max}+\phi_0$ where hv is incident energy

hv = 3 eV + 2.4 eV = 5.4 eV

∴ The frequency of the incident light is $v=\frac{5.4eV}{h}=\frac{5.4×1.6×10^{-19}J}{6.4×10^{-34}J}=13.5×10^{14}s^{-1}$