Question

if the angle of refraction is 90 then it is called as critical angle ?
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Answer 1

Answer:

no

critical angle is that angle which occurs when refraction stops and reflection occurs essentially when rays travel from denser to rarer medium

sin c=nr/nd

Answer 2

When light travels from denser to rarer medium, the angle of incidence at which angle of refraction is 90 degree is called critical angle of incidence . Answer: When light ray travels from a denser to rarer medium, the angle of incidence at which angle of refraction is 90 degree is called Critical Angle of incidence.