Wave property of electron implies that they will show diffraction effected . Davisson and Germer demonstrated this by diffracting electron from crystals . The law governing the diffraction from a crystals is obtained by requiring that electron waves reflected from the planes of atoms in a crystal inter fere constructiely

If a strong diffraction peak is observed when electrons are incident at an angle `i` from the normal to the crystal planes with distance `d` between them (see fig) de Brogle wavelength `lambda_(dB)` of electrons can be calculated by the relationship (n is an intenger)

Options

A. `dcos i=nlambda_(dB)`
B. `d sin i=nlambda_(dB)`
C. `2dcos i=nlambda_(dB)`
D. `2dsin i= n lambda_(nB)`

Explanation

The Bragg's relation for having an intensity, maximum for diffraction pattern is
`2dsin theta=n lambda` where `theta` is glancing angle,
Here, `theta=(90^(@)-i)`
`:. 2d sin (90^(@)-i)=n lambda` or `2d cosi=nlambda`