Red light of wavelength 625 nm is incident normally on a optical diffraction grating with `2xx10^(5)` lines/m. Including central principal maxima, how many maxima may be observed on a screen which is far from the grating?

Options

A. 15
B. 17
C. 8
D. 16

Answer

B

Explanation

For principal maxima in grating spectra
`(sin theta)/(N)= n lambda`
where, n=(1, 2, 3) is the order of principal maximum and `theta` is the angle of diffraction.
`n=(1)/(lambdaN)=(1)/(6.25xx10^(-7)xx2xx10^(5))=8`
`therefore` Number of maxima `=2n+1=2xx8+1=17`