Identify the correct statements among the following:
(A) An electromagnetic wave travels in vacuum like sound waves.
(B) An ultraviolet wave is not an electromagnetic wave.
(C) An electromagnetic wave can travel from earth to the planet, Saturn.
(D) An electromagnetic wave may have less velocity in a medium than in vacuum.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (C) and (D) only
(A) An electromagnetic wave travels in vacuum like sound waves. — Incorrect. Sound is a mechanical wave and needs a material medium, so it cannot travel through vacuum. An electromagnetic wave needs no medium.
(B) An ultraviolet wave is not an electromagnetic wave. — Incorrect. Ultraviolet radiation is part of the electromagnetic spectrum, between visible light and X-rays.
(C) An electromagnetic wave can travel from earth to the planet, Saturn. — Correct. Space between the planets is nearly vacuum, and electromagnetic waves travel through vacuum at \( c \).
(D) An electromagnetic wave may have less velocity in a medium than in vacuum. — Correct. In a medium the speed is lower than \( c \).
\( \displaystyle v = \frac{1}{\sqrt{\mu\varepsilon}} = \frac{c}{\sqrt{\mu_r\varepsilon_r}} \lt c \)
NCERT (2026-27):
Nature of Electromagnetic Waves – “… They differ from all the other waves we have studied so far, in respect that no material medium is involved in the vibrations of the electric and magnetic fields.”
Nature of Electromagnetic Waves – “… These replace ε0 and μ0 in the description to electric and magnetic fields in Maxwell’s equations with the result that in a material medium of permittivity ε and magnetic permeability μ, the velocity of light becomes,
\( \displaystyle v = \frac{1}{\sqrt{\mu\varepsilon}} \qquad (8.11) \)
Thus, the velocity of light depends on electric and magnetic properties of the medium.”