Choose the correct statements from the following:
(A) Electromagnetic waves do not follow the principle of superposition.
(B) The variations in the electric field and in the magnetic field of electromagnetic waves, if any, never happen simultaneously.
(C) Electromagnetic waves are produced by accelerated charges.
(D) The energy of electromagnetic waves is divided equally into electric and magnetic field vectors.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (C) and (D) only
In an electromagnetic wave the electric and magnetic fields oscillate in phase, at right angles to each other and to the direction of travel.
(A) Electromagnetic waves do not follow the principle of superposition. — Incorrect. Maxwell's equations are linear, so electromagnetic waves obey the principle of superposition; interference and diffraction of light depend on it.
(B) The variations in the electric field and in the magnetic field of electromagnetic waves, if any, never happen simultaneously. — Incorrect. The two fields vary in phase: they reach their maxima and their zeros at the same place and time.
(C) Electromagnetic waves are produced by accelerated charges. — Correct. An accelerated charge produces a changing electric field, which produces a changing magnetic field, and so on; a charge at rest or in uniform motion does not radiate.
(D) The energy of electromagnetic waves is divided equally into electric and magnetic field vectors. — Correct. With \( E = cB \) and \( c^{2} = 1/\mu_0\varepsilon_0 \), the two energy densities are equal.
\( \displaystyle \frac{1}{2}\varepsilon_0 E^{2} = \frac{1}{2}\varepsilon_0 c^{2}B^{2} = \frac{B^{2}}{2\mu_0} \)
NCERT (2026-27):
Sources of Electromagnetic Waves – “… It is an important result of Maxwell’s theory that accelerated charges radiate electromagnetic waves.”
Exercises – “… 8.10 In a plane electromagnetic wave, the electric field oscillates sinusoidally at a frequency of 2.0 × 1010 Hz and amplitude 48 V m–1. … (c) Show that the average energy density of the E field equals the average energy density of the B field.”