Calculate the angle of incidence and critical angle.

Question

Given the refractive index of flint glass = 1.61, the refractive index of water = 1.34, and the refractive index of air = 1.00.

a) Calculate the angle of incidence in the glass if light passes from flint glass into air and the angle of refraction = 80°

b) For light passing from flint glass into water, what is the value of the critical angle in degrees?

Answer 1

When light goes from denser medium to less dense medium, the light bends away from the normal.

The equation for this for case 1 is n_flint sin θ_flint = n_air sin θ_air. n_flint = 1.61, n_air ≈ 1.00, θ_air = 80°.

Solve for θ_{flint .} sin θ_flint = 1.00 x 0.98 / 1.61 = 0.61

θ_flint = arcsin (0.61) = 37.6°

Case 2: The critical angle for light going from flint glass to water is given by θ_c = arcsin (n_water / n_flint)

θ_c = arcsin (1.34 / 1.61) = 56.3°