'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
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