Total internal reflection of light can occur only when light travels from which type of medium to which other type of medium?

Introduction / Context:
Total internal reflection (TIR) is an important optical phenomenon used in fibre optics, prisms and many optical instruments. It occurs only under specific conditions related to the direction of light travel and the refractive indices of the media. This question tests whether you understand that TIR can take place only when light travels from an optically denser medium to an optically rarer medium and the angle of incidence exceeds a certain critical angle.

Given Data / Assumptions:

• Total internal reflection requires a pair of media with different refractive indices.
• The options list different combinations: air to glass, air to water, water to glass, and diamond to glass.
• We assume refractive index of diamond is greater than that of glass; glass is greater than that of water; water is greater than that of air.
• The question asks which pair allows TIR in principle.

Concept / Approach:
The two conditions for total internal reflection are: (1) Light must travel from a medium of higher refractive index (denser) to one of lower refractive index (rarer). (2) The angle of incidence in the denser medium must be greater than the critical angle for the interface. If light travels from a rarer to a denser medium (like air to glass or air to water), TIR cannot occur. Among the options, diamond has a higher refractive index than glass, so light going from diamond to glass is from denser to rarer medium and can, in principle, undergo total internal reflection if the incidence angle is sufficiently large.

Step-by-Step Solution:
Step 1: Recall that TIR requires light to move from a denser medium to a rarer medium.Step 2: Evaluate each option in terms of relative refractive index.Step 3: Air to glass: air is rarer, glass is denser; so this is rarer to denser and cannot give TIR.Step 4: Air to water: air is rarer, water is denser; again rarer to denser, TIR not possible.Step 5: Water to glass: water is less dense than glass in optical terms, so this is still rarer to denser; TIR not possible.Step 6: Diamond to glass: diamond has a higher refractive index than glass, so light travels from denser to rarer medium, satisfying the first condition for TIR.Step 7: Conclude that only the diamond to glass pair can show total internal reflection (for angles above the critical angle).

Verification / Alternative check:
Standard tables list refractive indices: diamond around 2.4, typical glass around 1.5, water around 1.33 and air close to 1. Light going from diamond (2.4) to glass (1.5) can undergo TIR. Light going from air (1.0) to glass, air to water or water to glass always travels from a lower to a higher refractive index, so only refraction and reflection occur, not total internal reflection.

Why Other Options Are Wrong:
In air to glass and air to water, light is incident from a rarer medium to a denser medium, so it bends toward the normal and TIR cannot occur in that direction. In water to glass, water has a lower refractive index than glass, so the transition is still from rarer to denser. TIR occurs only when light tries to leave the denser medium at a large angle, which is not the case in these options.

Common Pitfalls:
Students sometimes think that any interface can show total internal reflection, ignoring the requirement that light must attempt to go from denser to rarer. Another error is to associate TIR solely with glass without checking the relative indices. To answer correctly, always identify which medium is optically denser and ensure that light is travelling from that medium to a less dense one.

Final Answer:
Total internal reflection can take place when light travels from diamond to glass.