Question

If the electron has same momentum as that of a photon of wavelength $5200\stackrel{\circ }{A}$, then the velocity of electron in m /sec is given by

• A. ${10}^3$
• B. $1.4\times {10}^3$
• C. $7\times {10}^{-5}$
• D. $7.2\times {10}^6$

Answer 1

The correct option is B $1.4\times {10}^3$

If momenta of the electron and photon are equal, their wavelenghths should also be equal.
$\lambda =\frac{h}{mv}\Rightarrow v=\frac{h}{m\lambda }=\frac{6.6\times {10}^{-34}}{9.1\times {10}^{-31}\times 5200\times {10}^{-10}}\Rightarrow v=1.4\times {10}^{3}m/s$.