# With what velocity must an electron travel so that its momentum is equal to that of a photon of wavelength $\lambda=5200A^{\large\circ}$?

$(a)\;1400m/s\qquad(b)\;1200m/s\qquad(c)\;1235m/s\qquad(d)\;1300m/s$

$\lambda=\large\frac{h}{mu}$
Momentum ,$mu=\large\frac{h}{\lambda}$
$\Rightarrow \large\frac{6.625\times 10^{-34}}{5200\times 10^{-10}}$$Kgm/s$------(i)
Momentum of electron $=mu=9.108\times 10^{-31}\times u$------(ii)
Since both are same,therefore by (i) & (ii)
$9.108\times 10^{-31}\times u=\large\frac{6.625\times 10^{-34}}{5200\times 10^{-10}}$
$u=1400m/s$
Hence (a) is the correct answer.