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, which of the following statements 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 C The angular width of the central maximum will decrease

As the speed of an electron increases.
Its de-Broglie wavelength decreases

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

and angular width for central maxima is $\frac{2\lambda }{d}$

Using these relations the angular width of the central maxima will decrease.