A) when a ray moves from denser to rarer and incident angle is greater than critical angle
B) when a ray moves from rarer to denser and incident angle is less than critical angle
C) when a ray moves from rarer to denser and incident angle is equal to critical angle
D) none of the above
Correct Answer: A
Solution :
Total internal reflection is the phenomenon of reflection of light into a denser medium from an interface of denser medium and rarer medium. The essential conditions for total internal reflection are: (i) Light should travel from a denser medium to a rarer medium. (ii) Angle of incidence in denser medium should be greater than the critical angle for the pair of media in contact. We may define critical angle for a pair of media in contact as the angle of incidence in the denser medium corresponding to which angle of refraction in the rarer medium is \[{{90}^{o}}\]. It is represented by C and its value depends on the nature of media in contact. Note In total internal reflection, 100% of incident light is reflected back into the same medium, and there is no loss of intensity. That is why images formed by total internal reflection are much brighter than those formed by mirrors or lenses.
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