Light falls from glass to air. Find the angle of incidence for which the angle of deviation is 90o, if refractive index of glass is √2.
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Refractive index of glass = √2
Critical angle = Sin ⁻¹ 1/√2 = 45⁰
When a light ray from glass refracts into air, then angle of deviation is r - i (difference between angle of refraction and angle of incidence). This cannot be 90 deg. (as i and r are both less than 90 deg).
When a light rays gets totally internally reflected for (i > critical angle) then the angle of deviation can be 90 deg.
Then the angle of reflection = angle of incidence.
Around the point of incidence we have,
4 * angle of incidence + 2 * 90⁰ = 360⁰
Angle of incidence = 45⁰
As this angle is equal to or more than critical angle, total internal reflection takes place. Hence. that is the answer.
Critical angle = Sin ⁻¹ 1/√2 = 45⁰
When a light ray from glass refracts into air, then angle of deviation is r - i (difference between angle of refraction and angle of incidence). This cannot be 90 deg. (as i and r are both less than 90 deg).
When a light rays gets totally internally reflected for (i > critical angle) then the angle of deviation can be 90 deg.
Then the angle of reflection = angle of incidence.
Around the point of incidence we have,
4 * angle of incidence + 2 * 90⁰ = 360⁰
Angle of incidence = 45⁰
As this angle is equal to or more than critical angle, total internal reflection takes place. Hence. that is the answer.
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