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Draw a ray diagram to show the refraction of a monochromatic ray through a prism when it suffers minimum deviation.

Answer
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Hint: As we all know when a light deviates with a minimum amount after refraction through the prism, angle of incidence (i) and the angle of emergence (e) are equal.

Complete step by step answer:

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The above diagram shows the path of light traced when it passes through a prism such that the angle of deviation of light is minimum.
We know that deviation angle, δis given by
δ=i+eA
Where i is the angle of incidence
e is the emergent angle
A is the angle of prism.
Thus, the angle of deviation depends upon the angle of incidence. A plot between angle of deviation and angle of incidence is shown below from where it is clear that corresponding toi=e, δis minimum and for all other values of i, there are two values of δ.
So, at minimum deviationie.
δ=δm, i=e
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When a light deviates with a minimum amount, the angle of incidence and the angle of emergence are equal.
Also, the light inside the prism passes parallel to the base of prism BC.

Note:
If a ray enters the prism from air with a refractive index n1=1, the direction of the ray after it passes through the prism will depend only on its apex angle Q and the refractive index n of the glass from which prism is made. Passage of a ray through an optical prism is depicted in the picture above.
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