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) is an optical phenomenon where a wave of light striking the interface between two media is not refracted into the second medium but is entirely reflected back into the first medium. This question asks for the necessary conditions for TIR to occur.
Step 2: Detailed Explanation:
There are two fundamental conditions that must be met for total internal reflection to happen:
1. Direction of Travel: The light must be traveling from a medium with a higher refractive index (optically denser) to a medium with a lower refractive index (optically rarer). Therefore, statement B is correct and statement C is incorrect.
2. Angle of Incidence: The angle of incidence (\(\theta_i\)) in the denser medium must be greater than a specific angle called the critical angle (\(\theta_c\)). Therefore, statement A is correct.
Additionally, let's analyze statement D:
The critical angle is defined by Snell's Law when the angle of refraction is 90\textdegree. If \(n_1\) is the refractive index of the denser medium and \(n_2\) is that of the rarer medium, then:
\[ n_1 \sin(\theta_c) = n_2 \sin(90^\circ) \]
\[ \sin(\theta_c) = \frac{n_2}{n_1} \]
This formula clearly shows that the critical angle \(\theta_c\) depends on the refractive indices of both media. Therefore, statement D is correct.
Step 3: Final Answer:
The true statements are A, B, and D.