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Difficulty: EasyRefraction of Light, Total Internal Reflection, and Prisms

Which of the following conditions is necessary for total internal reflection to occur when light travels between two media?

  1. Light must travel from an optically denser medium to an optically less dense medium, and the angle of incidence must be greater than the critical angle.Answer
  2. B
    Light must travel from an optically less dense medium to an optically denser medium, and the angle of incidence must be greater than the critical angle.
  3. C
    Light must travel from an optically denser medium to an optically less dense medium, and the angle of incidence must be less than the critical angle.
  4. D
    Light must travel from an optically less dense medium to an optically denser medium, and the angle of incidence must equal zero degrees.

Answer

Total internal reflection requires light to travel from an optically denser medium to an optically less dense medium with an angle of incidence greater than the critical angle.
For total internal reflection to happen, two strict conditions must be satisfied: (1) light must travel from a medium with a higher refractive index to one with a lower refractive index, and (2) the angle of incidence must be strictly greater than the critical angle for that boundary.

Step-by-Step Solution

1
Identify the optical density requirement
Light must attempt to pass from a medium of higher refractive index (denser) into a medium of lower refractive index (less dense) so that the refracted ray bends away from the normal.
Bending away from the normal allows the angle of refraction to reach 90∘90^\circ at the critical angle.
2
Identify the angle of incidence requirement
The angle of incidence in the denser medium must exceed the critical angle (i>Ci > C).
When the incidence angle exceeds the critical angle, no refraction is possible and all energy is reflected back into the denser medium.

Key Concept

Conditions for Total Internal Reflection
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Topics

Refraction of Light, Total Internal Reflection, and Prisms

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