# What is the highest spectral order illuminated with 633-nm laser light?

What is the highest spectral order that can be seen if a grating with 6500 slits per cm is illuminated with 633-nm laser light? Assume normal incidence.
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Aryan Novak
Given values:
Number of slits per centimeter,
Wavelength,
Angle of diffraction, $\theta ={90}^{\circ }$
The phenomenon of bending of the light waves around the cornerns of obstacle is called diffraction.
The condition for diffraction maximum is given by,
$n\lambda =d\mathrm{sin}\theta$
Where,
n= Order of diffraction
$\lambda =$ Wavelength of light
d= Separation between the slits
$\theta =$ Angle of diffraction
The number of slits per centimeter is equal to the separation between the slits.
Number of slits per cm, $N=\frac{1}{d}$
Substituting equation
$n\lambda =\frac{\mathrm{sin}\theta }{N}\phantom{\rule{0ex}{0ex}}n=\frac{\mathrm{sin}\theta }{\lambda N}$
Substituting number of slits per centimeter, wavelength and angle of diffraction in equation