I keep getting “Total internal reflection” questions wrong in Ray Optics & Optical Instruments. What's the trap?
expecting TIR when light goes from rarer to denser medium.
The usual trap: expecting TIR when light goes from rarer to denser medium. How to avoid it: TIR needs dense-to-rare travel AND an angle beyond the critical angle. Go back to the definition — past a critical angle, light going from denser to rarer medium reflects entirely instead of refracting.
Key point
Total internal reflection
Common mistake
expecting TIR when light goes from rarer to denser medium.
Memory tip
TIR needs dense-to-rare travel AND an angle beyond the critical angle.
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