Question

A stream of electrons from a heated filament was passed between two charged plates kept at a potential difference $V$ esu. If $e$ and $m$ are charge and mass of an electron, respectively, then the value of $h/ \lambda$ (where $\lambda$ is wavelength associated with electron wave) is given by :

• A. $meV$
• B. $2 meV$
• C. $\sqrt{meV}$
• D. $\sqrt{ 2 meV}$

Answer 1

Answer: (D)

$\sqrt{ 2 meV}$

Answer 2

$\lambda = \frac{h}{P} = \frac{h}{\sqrt{2mE}} = \frac{h}{\sqrt{2me\,V}}$
$\Rightarrow \frac{h}{\lambda} = \sqrt{2me\,V}$