The wave properties of electrons implies that they will show diffraction effects. Davisson and Germer demonstrated this by diffracting electrons from crystals. The law governing the diffraction from a crystal is obtained by requiring that electron waves reflected from the planes of atoms in a crystal interfere constructively as shown in fig :
(i). Electrons accelerated by potential V are diffracted from a crystal. If d = 1Aͦ and i = 30°, V should be about (h = 6.6 × 10−34Js),
(me = 9.1 × 10−31kg,e = 1.6 × 10−19C)
(a) 1000V
(b) 2000V
(c) 50V
(d) 500V
(ii). What is the glancing angle in the above experiment?
(a) 30°
(b) 15°
(c) 45°
(d) 60°
(iii). 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, de- Broglie wavelength λdB of electrons can be calculated by the relationship (n is an integer) :
(a) dcosi = nλdB
(b) dsini = nλdB
(c) 2d cos i = nλdB
(d) 2d sin I = nλdB