Question

The speed of light is minimum in:

• A. Water
• B. Air
• C. Vacuum
• D. Glass

Hint:

A higher refractive index of a medium means light travels slower in it, compare the refractive indices of the four given media.

Answer 1

The Correct Option is D

Step 1: Recall how speed changes with medium.
Light travels fastest in vacuum, at \(3 \times 10^{8}\) m/s, and slows down when entering a denser optical medium.
Step 2: Connect speed with refractive index.
The refractive index of a medium is given by \(n = c/v\), so a higher refractive index means a lower speed of light in that medium.
Step 3: Compare refractive indices.
Vacuum has refractive index 1, air is very close to 1, water is about 1.33, and glass is about 1.5, the highest among these four.
Step 4: Draw the conclusion.
Since glass has the highest refractive index of the four media listed, light travels slowest in glass.
Step 5: Rule out other options.
Vacuum and air allow light to travel close to its maximum speed. Water slows light down less than glass does.
Final Answer: D) Glass.