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Total internal reflection of light can occur only when light is travelling under which of the following conditions?
AFrom rarer to denser medium, at any angle of incidence
BFrom rarer to denser medium, along the normal direction
CFrom denser to rarer medium, beyond the critical angle
DBetween two media having equal refractive indices
Answer & Solution
Correct answer: C. From denser to rarer medium, beyond the critical angle
1. Total internal reflection requires the refracted ray to bend away from the normal, which happens only when going from denser to rarer medium.
2. The chapter states that for angles of incidence larger than the critical angle, the angle of refraction exceeds 90 degrees and all light returns to the dense medium.
3. Going rarer to denser bends towards the normal and never gives r > 90 degrees, so that distractor fails.
4. Hence the correct condition is denser to rarer, beyond the critical angle.
_Source: Balbharati (Maharashtra Board) Class 10 Science & Technology, Ch 6 "Refraction of Light", p.87_
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