Direction : Question Numbers. 150 and 151 are based on the following paragraph.
Wave property 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 (See figure).

Electrons accelerate by potential V are diffracted from a crystal. If `d=1Å` and `i=30^(@)`, V should be about `(h=6.6xx10^(-34)Js,m_(e)=9.1xx10^(-31)kg,e=1.6xx10^(-19)C)`

Options

A. 1000 V
B. 2000 V
C. 50 V
D. 500 V

Answer

C

Explanation

According to Bragg.s law
`2d sin theta= nlambda`
`:.` for first order diffraction,
`2d sin (90^(@)-30^(@))=lambda`
`lambda=2xx1xx(sqrt(3))/(2)=sqrt(3)Å`
Now `lambda=(h)/(sqrt(2meV)) rArr V=(h^(2))/(2melambda^(2))`
`V=((6.6xx10^(-34))^(2))/(2xx9xx10^(-31)xx1.6xx10^(-19)xx3xx10^(-20))`
`V=50 V`