Question

when will angle of refraction be equal to 90°?

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Answer 1

Answer:When the angle of incidence is equal to the critical angle, the angle of refraction is equal to 90 degree.

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Explanation: If the angle of incidence is bigger than this critical angle, the refracted ray will not emerge from the medium, but will be reflected back into the medium.

Answer 2

Explanation:

Angle of refraction will be zero. Because, for the light to refract it has enter into the second medium.

At 90° as angle of incidence the light only glides on the interface. So there will be no refraction.