Which of the following statements are correct?
A. In a region of free space with electric field E, there is an energy density \( \displaystyle\frac{1}{2}\varepsilon_0E^{2} \)
B. An electromagnetic wave contains both electric and magnetic field.
C. Electromagnetic waves do not exert pressure
D. Hertz could not establish the wave nature of radiation.
E. No material medium is required for vibrations of electric field and magnetic field.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A, B and E only
(A) In a region of free space with electric field E, there is an energy density \( \frac{1}{2}\varepsilon_0E^{2} \) — Correct. An electric field stores energy in the space it occupies, with energy per unit volume \( u_E = \frac{1}{2}\varepsilon_0E^{2} \).
(B) An electromagnetic wave contains both electric and magnetic field. — Correct. It consists of oscillating electric and magnetic fields, perpendicular to each other and to the direction of propagation.
(C) Electromagnetic waves do not exert pressure — Incorrect. The waves carry energy and momentum, so they exert radiation pressure on a surface that absorbs or reflects them.
(D) Hertz could not establish the wave nature of radiation. — Incorrect. Hertz produced and detected electromagnetic waves, and showed that they undergo reflection, refraction, diffraction and polarisation like light, which established their wave nature.
(E) No material medium is required for vibrations of electric field and magnetic field. — Correct. Electromagnetic waves travel through vacuum; the changing fields sustain each other.
Note: Statements (B) and (E) of this question are from the latest textbook (2026-27). Statements (A), (C) and (D), on the energy density of an electric field, radiation pressure and Hertz’s experiments, are printed only in the pre-rationalised textbook (2022-23). They were removed from the latest book, and they also appear to be out of the CUET 2026 syllabus.
NCERT (2026-27):
Nature of Electromagnetic Waves – “It can be shown from Maxwell’s equations that electric and magnetic fields in an electromagnetic wave are perpendicular to each other, and to the direction of propagation.”
Nature of Electromagnetic Waves – “… They are self-sustaining oscillations of electric and magnetic fields in free space, or vacuum. 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.”
NCERT (Pre-rationalised edition, 2022-23):
Nature of Electromagnetic Waves – “… We have seen in chapter 2 that in a region of free space with electric field E, there is an energy density (ε0E2/2). … Since it carries momentum, an electromagnetic wave also exerts pressure, called radiation pressure.”
Nature of Electromagnetic Waves – “… Hertz not only showed the existence of electromagnetic waves, but also demonstrated that the waves, which had wavelength ten million times that of the light waves, could be diffracted, refracted and polarised. Thus, he conclusively established the wave nature of the radiation.”