Red light of wavelength $625\ nm$ is incident normally on an optical diffraction grating with $2 imes 10^{5}lines/m$. Including central principal maxima, how many maxima may be observed on a screen which is far from the grating

Question

Red light of wavelength $625\ nm$ is incident normally on an optical diffraction grating with $2 	imes 10^{5}lines/m$. Including central principal maxima, how many maxima may be observed on a screen which is far from the grating

Dr. Abubacker · Accepted Answer

(b) Here, wavelength, $\lambda = 625nm = 625 	imes 10^{- 9}m$
Number of lines per meter, $N = 2 	imes 10^{5}$
For principal maxima is grating spectra $\frac{\sin	heta}{N} = n\lambda$,
Where $n( = 1,2,3)$ is the order of principal maxima and $	heta$ is the angle of diffraction
The maximum value of $\sin	heta$ is 1
$	herefore n = \frac{1}{N\lambda} = \frac{1}{2 	imes 10^{5} 	imes 625 	imes 10^{- 9}} = 8$
$	herefore$ Number of maxima $= 2n + 1 = 2 	imes 8 + 1 = 17$

Q. Red light of wavelength $625\ nm$ is incident normally on an optical diffraction grating with $2 \times 10^{5}lines/m$. Including central principal maxima, how many maxima may be observed on a screen which is far from the grating

Explanation

Reviewed by Dr. Abubacker

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