Question

The source of electromagnetic waves can be

• A. A charge moving with a constant velocity.
• B. An accelerated charge.
• C. A charge at rest.
• D. A charge moving parallel to a magnetic field.

Hint:

A fundamental result of Maxwell's theory is: \[ \text{Accelerated Charge} \Longrightarrow \text{Electromagnetic Radiation} \] A charge at rest or moving with constant velocity does not radiate electromagnetic waves.

Answer 1

The Correct Option is B

Concept: Electromagnetic waves are produced whenever an electric charge undergoes acceleration. A changing electric field produces a magnetic field and a changing magnetic field produces an electric field, resulting in the propagation of electromagnetic waves.

Step 1:Examine a charge at rest. A stationary charge produces only a static electric field. \[ {\text{No electromagnetic waves are produced.}} \]

Step 2: Examine a charge moving with constant velocity. A uniformly moving charge produces constant electric and magnetic fields. There is no changing field pattern required for radiation. \[ {\text{No electromagnetic waves are produced.}} \]

Step 3: Examine an accelerated charge. When a charge accelerates, \[ \text{Electric field changes with time} \] and \[ \text{Magnetic field changes with time} \] These changing fields propagate through space as electromagnetic waves. \[ {\text{Electromagnetic waves are emitted.}} \]

Step 4: State the answer. \[ { \text{An accelerated charge is the source of electromagnetic waves.} } \] Hence, the correct option is \[ {(B)} \]