Question

Out of the following options which one can be used to produce a propagating electromagnetic wave?
A. A charge moving at constant velocity
B. A stationary charge
C. A charge less particle
D. An accelerating charge

Answer 1

Hint: An electromagnetic wave is produced when there is a change in the electric and magnetic field due to a charge. We need to check all the given options for which there is a change taking place in the electric and magnetic field on acceleration or deceleration in order to find the correct answer.

Complete step-by-step answer:
An electric charge at rest will produce an electric field around it while a moving charge will produce an electric as well as magnetic field around it.
The electromagnetic waves are produced when there is a sudden change in the electric and magnetic field of a moving charge.
A stationary charge cannot produce the electromagnetic waves as its electric field stays constant while it is at rest. A charge moving at constant velocity also cannot produce electromagnetic waves as the constant motion means that there is no change in the electric and magnetic field of the moving charge.
The electromagnetic waves are produced only when an electric charge undergoes acceleration or deceleration. The change in the electric and the magnetic field of the charge on acceleration or deceleration is manifested in the form of electromagnetic waves.

So, the correct answer is “Option d”.

Note: 1. A charge less particle cannot produce any electromagnetic wave as there is no electric or magnetic field associated with it and changes in electric and magnetic fields are necessary because of electromagnetic waves.
2. The actual principle behind the production of electromagnetic waves from an accelerating or a decelerating charge is related with the conservation of electromagnetic energy of the charge undergoing acceleration or deceleration.