An electron accelerated through a potential of 10000 V from rest has a de Broglie wavelength `lamda`. What should be the accelerating potential so that the wavelength is doubled?

Options

A. 20000 V
B. 40000 V
C. 5000 V
D. 2500 V

Answer

D

Explanation

The stored energy in the electron accelerated through a potential of 10000 V,
E = hf
or, `10000 xx e = (hc)/(lamda)` [where e = charge of electron `lamda`= de Broglie wavelength of the electron]
or, `5000 xx e = (hc)/(2lamda)`
The accelerating potential should be 5000 V so that the wavelength is doubled.