In: Physics
Laser light from argon ion laser of wavelength 488.0 nm passes through a diffraction grating. The first bright spots occur at an angle 6.726 degree left and right from the central maximum. How many additional pares of bright spots are there beyond the first bright spots?
Wavelength = 488 nm
= 488 x10 -9 m
Angle of first bright spot = 6.726 o
Condition for first bright spot is d sin =
from this grating element d = / sin
= 4.1666 x10 -6 m
Number of lines per meter in grating N = 1/ d
= 240000
Maximum order n = d / at maximum order sin = 1.So, d sin = n
d = n
n = 8.53
So, number of pairs of bright spots n = 8
Additional pairs of bright spots are there beyond the first bright spots = n -1
= 7