The source of electromagnetic waves can be

The correct answer is Option (2) → an accelerated charge.

Electromagnetic waves are produced by an accelerated charge. Its changing velocity makes its electric field change with time; the changing electric field produces a changing magnetic field, which in turn produces a changing electric field, and this disturbance travels outward as a wave. A charge at rest or moving uniformly has fields that do not radiate.

Option (1) a charge moving with a constant velocity. — Incorrect. A charge moving with constant velocity is a steady current; it produces a steady magnetic field but no radiation.

Option (2) an accelerated charge. — Correct. Acceleration makes the fields of the charge vary with time, which is the source of the wave; an oscillating charge radiates at its frequency of oscillation.

Option (3) a charge at rest. — Incorrect. A charge at rest has only a static electric field.

Option (4) a charge moving parallel to a magnetic field. — Incorrect. A charge moving parallel to a magnetic field feels no magnetic force (\( \sin 0^\circ = 0 \)), so it moves with constant velocity and does not radiate.

NCERT (2026-27):
Sources of Electromagnetic Waves – “How are electromagnetic waves produced? Neither stationary charges nor charges in uniform motion (steady currents) can be sources of electromagnetic waves. The former produces only electrostatic fields, while the latter produces magnetic fields that, however, do not vary with time. It is an important result of Maxwell’s theory that accelerated charges radiate electromagnetic waves.”