Question

White light is spread out into spectral hues by a diffraction grating. If the grating has 1000 lines per cm, at what angle will red light (λ = 640 nm) appear in first order?

Answer 1

3.67°

Explanation: Given that λ=640nm , m = 1

Considering the slit separation

d = 1cm/1000

= 1.000×10^-3cm

= 1.000×10-5m

We then have

Sinθ = mλ/d

Sinθ= (1×640×10^-9)/1.000×10-5m

Sinθ = 0.064

θ= sin-1 0.064

θ= 3.669°

= 3.67°