Light is incident normally on a diffraction grating through which the first order diffraction is seen at `32^@`. The second order diffraction will be seen at

Options

A. at`80^@`
B. at`64^@`
C. at`48^@`
D. there is no ssecond order diffraction

Answer

D

Explanation

Angle of first order of diffraction `(theta_(1)) = 32^(@)` . We know that the angle of diffraction for the nth order `(theta_(n))` is given by `d sin theta_(n) = n lambda`.
For first order diffraction we get
`d sin 32^(@) = 1 xx lambda or , lambda = d sin 32^(@)`
Now for second order diffraction ,
`d sin theta_(2) = 2 xx lambda or , d sin theta_(2) = 2 xx d sin 32^(@)`
or `sin theta_(2) = 2 xx sin 32^(@) = 2 xx 0.529 = 1.06`
Since the sine of any angle cannot be greater than 1, therefore there is no second order diffraction.