Practice portal › Ray Optics and Optical Instruments › Refraction through a Prism
Asked in GUJCET 2025 · Deviation and minimum deviation
Given: an equilateral prism, so the refracting angle is A=60°, and the angle of minimum deviation is δₘ=46°.
Idea: minimum deviation happens on the symmetric path, where the angle of incidence equals the angle of emergence. Then δₘ=i+e-A becomes δₘ=2i-A.
Rearranging, i=(A+δₘ)/2.
i=(60°+46°)/2=(106°)/2.
So the ray must strike the face at 53°.
As a check, this prism's glass has n=(sin 53°)/(sin 30°)=1.6, an ordinary value for flint glass.
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