Total internal reflection can take place only if: - Vidyadip

MCQ

Total internal reflection can take place only if:

A
Light goes from optically rarer medium $($smaller refractive index$)$ to optically denser medium.
✓
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

Correct option: B.

Light goes from optically denser medium to rarer medium.

$T.I.R. ($Total Internal reflection$)$
$i < C ($condition for $T.I.R.)$
By Snell's Law
$\text{n}_1\sin\text{i}=\text{n}_2\sin90^{\circ}$
$\sin\text{i}=\frac{\text{n}_2}{\text{n}_1}=\sin\text{C}$
$\text{þ} \ \text{C}=\sin^{-1}$
$\because \ -1\leq\sin\text{i}\leq1$
$n_1 > n_2($ 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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