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'O' Level Standard Questions - Refraction

Q5. Two faces of a glass prism with a refractive index of 1.50 have an angle of 40° between them.

A ray of light is incident on one of the faces at an angle of 45°.

Trace the path of the ray through the prism and find the angle between the direction of the ray entering the prism and the direction of the ray leaving the prism.

Snell's Law: n1sin θ1 = n2sin θ2

nairsin θair = nglasssin θglass

1 x sin 45o = 1.50 x sin θglass

sin θglass= sin 45o/1.50 = 0.471

θglass= 28o

We now need to calculate a few angles....

nairsin = nglasssin θglass

sin θair= 1.50 x sin 12o

sin θair= 0.312

θair= 18o

 

Therefore the ray changes direction by 23o