If the speeds of gamma rays, X-rays and microwaves are \( V_g \), \( V_x \) and \( V_m \), respectively in free space, then the correct relation between them is
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → \( V_g = V_x = V_m \)
Gamma rays, X-rays and microwaves are all electromagnetic waves. In free space every electromagnetic wave travels with the same speed \( c = 1/\sqrt{\mu_0\varepsilon_0} = 3\times10^{8}\,\mathrm{m\,s^{-1}} \), whatever its frequency or wavelength. They differ in frequency and wavelength, not in speed.
\( \displaystyle V_g = V_x = V_m = c \)
Option (4) \( V_g = V_x = V_m \) — Correct. All three travel at \( c \) in free space.
NCERT (2026-27):
Nature of Electromagnetic Waves – “… The velocity of electromagnetic waves in free space or vacuum is an important fundamental constant. It has been shown by experiments on electromagnetic waves of different wavelengths that this velocity is the same (independent of wavelength) to within a few metres per second, out of a value of 3×108 m/s. The constancy of the velocity of em waves in vacuum is so strongly supported by experiments and the actual value is so well known now that this is used to define a standard of length.”