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Geometrical Optics — Physics STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 SciencePhysicsGeometrical Optics1 Mark
Question
Total internal reflection can take place only if:
  1. Light goes from optically rarer medium (smaller refractive index) to optically denser medium.
  2. Light goes from optically denser medium to rarer medium.
  3. The refractive indices of the two media are close to each other.
  4. 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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