Question

Which statements are true for total internal reflection?
A. The angle of incidence must be greater than the critical angle
B. light goes from an optically denser medium to an optically rarer medium.
C. light goes from an optically rarer medium to an optically denser medium.
D. The critical angle depends on the refractive index of both media.
Choose the correct answer from the options given below:

• A. A, B and C only
• B. A, B and D only
• C. A, B, C and D
• D. B, C and D only

Hint:

To remember the conditions for TIR, think of light trying to "escape" from a slow medium (like water) into a fast medium (like air). It can only escape if its angle is not too shallow. If it's too shallow (i.e., angle of incidence is too large), it gets trapped and reflects back.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Total Internal Reflection (TIR) occurs when light, traveling from one medium to another, is entirely reflected back into the first medium instead of being refracted. This question requires identifying the conditions necessary for TIR.
Step 2: Detailed Explanation:
Two key conditions must be satisfied for total internal reflection:
1. Direction of Travel: Light must travel from a medium with a higher refractive index (denser) to a medium with a lower refractive index (rarer). Thus, statement B is correct, and statement C is incorrect.
2. Angle of Incidence: The angle of incidence (\(\theta_i\)) in the denser medium must exceed the critical angle (\(\theta_c\)). Hence, statement A is correct.
Analyzing statement D:
The critical angle is defined using Snell's Law when the angle of refraction equals 90\textdegree. If \(n_1\) represents the refractive index of the denser medium and \(n_2\) that of the rarer medium:
\[ n_1 \sin(\theta_c) = n_2 \sin(90^\circ) \]
\[ \sin(\theta_c) = \frac{n_2}{n_1} \]
This equation demonstrates that the critical angle \(\theta_c\) depends on the refractive indices of both media. Consequently, statement D is correct.
Step 3: Final Answer:
The correct statements are A, B, and D.