If $\lambda_0$ and $\lambda$ be threshold wavelength and wavelength of incident light, the velocity of photoelectron ejected from the metal surface is:
(1) $\sqrt{\frac{2h}{m}\left(\lambda_0 - \lambda\right)}$
(2) $\sqrt{\frac{2hc}{m}\left(\lambda_\mathrm{o} - \lambda\right)}$
(3) $\sqrt{\frac{2hc}{m}\left(\frac{\lambda_0 - \lambda}{\lambda\lambda_0}\right)}$
(4) $\sqrt{\frac{2h}{m}\left(\frac{1}{\lambda_\mathrm{o}} - \frac{1}{\lambda}\right)}$