JEE Main · 2016 · 03 Apr 2016 · Offline · Atomic Structure

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 / λ

(where

λ

is wavelength associated with electron wave) is given by :

Answer: (C)

Solution

The plates accelerate the electron through potential

V

, giving it kinetic energy

e V = \frac{1}{2} m v^{2}

, so

v = \frac{2 e V}{m}

. The de Broglie relation

λ = \frac{h}{m v}

then gives

\frac{h}{λ} = m v = m \frac{2 e V}{m} = 2 m e V

JEE Main · 2016 · 03 Apr 2016 · Offline · Single correct option