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Ray Optics and Optical Instruments — Physics STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 SciencePhysicsRay Optics and Optical Instruments1 Mark
MCQ

Total internal reflection can take place only if:

  • A
    Light goes from optically rarer medium (smaller refractive index) to optically denser medium.
  • B
    Light goes from optically denser medium to rarer medium.
  • C
    The refractive indices of the two media are close to each other.
  • D
    The refractive indices of the two media are widely different.
✓

Answer

  1. Light goes from optically denser medium to rarer medium.

Explanation:

T.I.R. (Total Internal reflection)

i < C (condition for T.I.R.)

By Snell's Law

$\text{n}_1\sin\text{i}=\text{n}_2\sin90^{\circ}$

$\sin\text{i}=\frac{\text{n}_2}{\text{n}_1}=\sin\text{C}$

$\text{þ} \ \text{C}=\sin^{-1}$

$\because \ -1\leq\sin\text{i}\leq1$

n1 > n2 (so we can conclude that light goes from optically denser medium to rarer medium & incident angle is greater than the critical angle.)

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