Question

1)What color of laser light shines through a diffraction grating with a line density of 500 lines/mm if the third maxima from the central maxima (m=3) is at an angle of 45°? Show all work in your answer.

Hint: Calculate the wavelength then use Table 1 to identify the color.​

2) How would the interference pattern produced by a diffraction grating change if the laser light changed from red to blue?

Answer 1

(a)

condition for diffraction maxima

d sin theta = m lamda

lamda = ( 1/N) sin theta /m

= ( mm/500 lines) sin 45 /3

=(10^-3/500)sin 45/3

=471.3 nm

it is blue color wavelength

(b) if we change red color light instead of blue light wave length increase so number maxima from the central decreases

so m values less than 3

if we take lamda 620 nm we get m = 2

if we take lamda 750 nm we get m = 1