Question

Q) A parallel beam of fast moving electrons is incident
normally on a narrow slit. A fluorescent screen is
placed at a large distance from the slit. If the
speed of the electrons is increased, which of the
following statements is correct? [NEET-2013]

(1) The angular width of the central maximum of the diffraction pattern will increase

(2) The angular width of the central maximum will
decrease

(3) The angular width of the central maximum will be unaffected

(4) Diffraction pattern is not observed on the screen in the case of electrons​

Answer 1

Answer:

We know that \lambda=\dfrac{h}{mv}λ=  

mv

h

​  Also for angular width

\omega=\dfrac{2\lambda}{d}ω=  

d

2λ

​  So we can say \omega\propto\lambda\propto \dfrac{1}{v}ω∝λ∝  

v

1

​  So if the velocity increases, the angular width of the central maximum will decrease.

Explanation: