'O' Level Standard Questions - Refraction

Q1.

(a) A ray of light falls on a glass block and the angle of incidence is 45°. If the angle of refraction is 30°, what is the refractive index of the glass?

Refractive index of air = 1

 

Snell's Law: n1sin θ1 = n2sin θ2

nairsin θair = nglasssin θglass

sin 45o = nglasssin 30o

nglass= sin 45o /sin 30o

nglass = 0.707/0.500

nglass = 1.41

(b) If the angle of incidence of a ray of light falling on water is 65° and the refractive index of water is 1.33, calculate the angle of refraction.

nairsin θair = nwatersin θwater

sin 65o = 1.33 x sin θwater

sin θwater= sin 65o/1.33

sin θwater= 0.906/1.33 = 0.681

θwater= 42.9o

(c) A ray of light is refracted as it travels out of glass into air. If that glass has a refractive index of 1.50 and the angle of incidence is 20°, what is the angle of refraction as it enters the air?

nairsin θair = nglasssin θglass

sin θair = 1.50 x sin 20o

sin θair= 0.51

θair= 31o