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Which of the following conditions are necessary and sufficient for total…

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PHYSICS

Which of the following conditions are necessary and sufficient for total internal reflection to take place at the boundary between two optical media?

  • I. Light is passing from optically denser medium to optically less dense medium
  • II. Light is passing from optically less dense medium to optically denser medium
  • III. Angle of incidence is greater
  • IV. Angle of incidence is lesser

A. I and II only

B. II and III only

C. III and IV only

D. I and III only

QUICK ANSWER…

D

DETAILS…  

Total internal reflection, as the name implies is simply the complete reflection of light at the boundary when light travels from a denser medium to a less dense medium.

For instance, if light is traveling from water to air, it is possible to totally reflect the light back to the water at the junction. This phenomenon is called total internal reflection.

For this to happen, two conditions must be met.

  1. Light must be travelling from a denser medium to a less dense medium.
  2. The angle of incidence of this light at the boundary must be greater than the critical angle.

Now for the right answer to the above question:

  1. A is not the right answer. I and II cannot be correct at the same time.
  2. B is incorrect. no, its from denser to less dense medium.
  3. C is incorrect. III and IV cannot be correct at the same time.
  4. D is correct.

KEY-POINTS…

You may please note this/these:

  • For total internal reflection to occur, two conditions must be met.
  • Light must be travelling from the denser medium to the less dense medium.
  • The angle of incidence must be greater than the critical angle.
  • If the angle of incidence is same as the critical angle, the ray will travel along the surface.
  • If the angle of incidence is less than the critical angle, the ray will not reflect inwards but there will be refraction.

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/ culled from 2020 JAMB-UTME physics past question 29 /

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