With what velocity must an electron travel so that its momentum is equal to that of photon with a wavelength of $\lambda =5200 \stackrel{\mathrm{o}}{\mathrm{A}}$

Momentum of photon having wavelength $\lambda$ is

$p=\frac{h}{\lambda }=\frac{6.626\times {10}^{-34}}{5200\times {10}^{-10}} {\mathrm{kgms}}^{-1}$

Momentum of electron moving with a velocity $p$ is

$p_e=mv=9.1\times {10}^{-31}v$

Since the photon and the electron have same momentum

$\Rightarrow 9.1\times {10}^{-31}v=\frac{6.626\times {10}^{-34}}{5200\times {10}^{-10}}$

$\Rightarrow v=1400 {\mathrm{ms}}^{-1}$