Choose the correct statements from the following.
A. Like light waves, thermal radiations are also electromagnetic radiation.
B. Electromagnetic waves can travel in vacuum but mechanical waves cannot do so.
C. Gamma rays are more energetic than X-rays.
D. Microwaves are heat waves so they always produce heating.
E. Displacement current is a fictitious current and has nothing in common with conduction current.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A, B and C only
Each statement is judged separately against the properties of electromagnetic waves.
(A) Like light waves, thermal radiations are also electromagnetic radiation — Correct. Thermal radiation from a hot body is mainly infrared, which is part of the electromagnetic spectrum like visible light.
(B) Electromagnetic waves can travel in vacuum but mechanical waves cannot do so — Correct. An electromagnetic wave is a self-sustaining oscillation of electric and magnetic fields and needs no medium, whereas a mechanical wave needs a material medium.
(C) Gamma rays are more energetic than X-rays — Correct. Gamma rays lie beyond X-rays in the spectrum, with higher frequency, and the photon energy is \( E = h\nu \).
(D) Microwaves are heat waves so they always produce heating — Incorrect. The waves called heat waves are the infrared waves. Microwaves cause heating only in a material that absorbs them, such as water in food.
(E) Displacement current is a fictitious current and has nothing in common with conduction current — Incorrect. The displacement current \( \varepsilon_0\,d\Phi_E/dt \) is a real source of magnetic field, exactly like a conduction current (Ampere-Maxwell law), so it does have something in common with it.
The correct statements are A, B and C, which is Option (2).
NCERT (2026-27):
Infrared Waves – “… Infrared waves are sometimes referred to as heat waves.”
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.”
Gamma Rays – “They lie in the upper frequency range of the electromagnetic spectrum and have wavelengths of from about 10–10m to less than 10–14m.”
Displacement Current – “… In all respects, the displacement current has the same physical effects as the conduction current.”