Question

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, then which of the following is correct?

• A. Diffraction pattern is not observed on the screen in the case of electrons
• B. The angular width of the central maximum of the diffraction pattern will increase
• C. The angular width of the central maximum will decrease
• D. The angular width of the central maximum will be unaffected

Answer 1

The correct option is B

The angular width of the central maximum of the diffraction pattern will increase

Angular width $\propto \frac{1}{\lambda }$

$\lambda =\frac{h}{mv}$

$\lambda \propto \frac{1}{v}$

If velocity of electron increases then l decreases hence angular width increases.