A photon of wavelength 400 nm passes through the following media. Arrange them in the descending order of the photon velocities in them.
A. Crown glass
B. Water
C. Diamond
D. Air
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → D, B, A, C
The speed of light in a medium is \( v = c/n \), so the larger the refractive index, the slower the light travels.
\( \displaystyle v = \frac{c}{n} \)
\( \text{Air (D): } n \approx 1.0003 \)
\( \text{Water (B): } n \approx 1.33 \)
\( \text{Crown glass (A): } n \approx 1.52 \)
\( \text{Diamond (C): } n \approx 2.42 \)
Refractive index increases in this order, so the speed decreases: D, B, A, C.
NCERT (2026-27):
Total Internal Reflection – …
