A diffraction grating with 270 lines per mm is used in an experiment to study the visible spectrum of a gas discharge tube. 1. At what angle from the beam axis will the fourth order peak occur if the tube emits light with wavelength of 665.0 nm?2. At what angle will the second order peak occur?

1) θ = 45.91°

2) θ = 21.04°

Explanation:

We are given;

Wavelength; λ = 665 nm = 6.65 × 10^(-7) m.

Distance between slits; d = 1mm/270 = 1/270 mm = (1/270) × 10^(-3) m

1) To find the angle, we will use the formula;

d sin θ = mλ

Where m is the order of peak which in this question is 4.

Thus, we have;

sin θ = mλ/d

sin θ = (4 × 6.65 × 10^(-7))/((1/270) × 10^(-3))

sin θ = 0.7183

θ = sin^(-1) 0.7183

θ = 45.91°

2) Similarly, d sin θ = mλ

Where m is the order of peak which in this question is 2. Thus;

sin θ = (2 × 6.65 × 10^(-7))/((1/270) × 10^(-3))

sin θ = 0.3591

θ = sin^(-1) 0.3591

θ = 21.04°