Total Internal Reflection

Total internal reflection occurs when light travels from a denser medium to a less dense medium and the angle of incidence is greater than the critical angle. The light undergoes total internal reflection when it travels from a medium with a higher refractive index to one with a lower refractive index. - In the case of air to water, the light travels from air (refractive index ) to water (refractive index ). Total internal reflection can occur for certain angles of incidence. - For other options, the refractive index of the second medium is either equal or smaller, preventing total internal reflection.

The correct option is (C): 30°

Step 1: Understanding the Concept:
The critical angle is a specific angle of incidence that occurs only when light travels from a denser medium to a rarer medium. It is the boundary condition for the phenomenon of total internal reflection.

Step 2: Key Formula or Approach:
According to Snell's Law of refraction: where and are the refractive indices of the first (denser) and second (rarer) media, and and are the angles of incidence and refraction, respectively. The critical angle ( ) is the angle of incidence ( ) for which the angle of refraction ( ) is exactly 90°. At this point, the refracted ray grazes the boundary between the two media.

Step 3: Detailed Explanation:
When light travels from a denser medium ( ) to a rarer medium ( ), where , as the angle of incidence increases, the angle of refraction also increases. There exists a particular angle of incidence, called the critical angle , for which the angle of refraction becomes 90°. Setting and in Snell's Law: Since , we get: If the angle of incidence is greater than the critical angle ( ), the light ray does not refract into the rarer medium at all; instead, it is completely reflected back into the denser medium. This phenomenon is called total internal reflection. Therefore, the critical angle is defined as the angle of incidence that results in an angle of refraction of 90°. The other options are incorrect: the angle of reflection is always equal to the angle of incidence, so it would be , not 0° or 90°. An angle of refraction of 0° corresponds to normal incidence ( ).

Step 4: Final Answer:
The critical angle is the angle of incidence for which the angle of refraction is 90°.

Step 1: Understanding the Concept:
This question tests the conditions and phenomena associated with Total Internal Reflection (TIR). We need to evaluate each statement for its correctness.

Step 2: Detailed Explanation:
(A) Total internal reflection occurs when a ray of light travels from a rarer transparent medium to a denser medium.
This is incorrect. A necessary condition for TIR is that the light must travel from a denser medium to a rarer medium. So, this statement is false.
(B) In total internal reflection, the incident ray of light remains in the same medium after reflection.
The term "reflection" itself implies that the ray bounces back into the original medium. In total internal reflection, the entire ray is reflected, so it certainly remains in the same (denser) medium. This statement is true.
(C) In total internal reflection, the angle of incidence inside the denser transparent medium is equal to the angle of reflection in the same medium.
Total internal reflection is still a reflection phenomenon. Therefore, it must obey the laws of reflection. The first law of reflection states that the angle of incidence is equal to the angle of reflection ( ). This statement is true.
(D) In total internal reflection inside a denser medium there is no angle of refraction.
TIR occurs when the angle of incidence exceeds the critical angle. Under this condition, no light passes into the rarer medium, meaning there is no refracted ray. Consequently, there is no angle of refraction to be measured. This statement is true.

Step 3: Final Answer:
Statements (B), (C), and (D) are correct, while statement (A) is incorrect. The correct option is the one that includes (B), (C), and (D).