Total Internal Reflection
2 marks · EasyExplain why total internal reflection does not occur when light travels from air into glass, even if the angle of incidence is large.
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Total internal reflection only happens when light moves from a more optically dense medium to a less optically dense medium, like from glass to air. When light travels from air to glass (from a less to a more dense medium), it cannot be totally internally reflected.
Also accept: Because light must go from dense to less dense medium for total internal reflection to occur.
Common mistakes: Confusing direction of total internal reflection.; Thinking it happens any time angles are large.
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Marking points
B1 · 1 mark · States total internal reflection needs light to travel from a denser to a less dense medium.
B1 · 1 mark · States that in air to glass light goes from less to more dense, so total internal reflection cannot occur.
Worked solution
Total internal reflection only happens when light moves from a medium with higher refractive index (denser) to a lower one. Air to glass is the opposite, so total internal reflection is not possible regardless of the angle.