Q.An accelerating (oscillating) electric charge is said to be the source of an electromagnetic wave. Explain, in your own words, how an oscillating charge produces a self-sustaining electromagnetic wave, referring to the way a changing electric field creates a magnetic field and a changing magnetic field creates an electric field in turn.

Starting point: the oscillating charge. As the charge accelerates back and forth (Section 8.3), the electric field it produces at nearby points in space is continuously CHANGING in time, since the charge's own position (and hence the field pattern around it) keeps changing.

Step 1: changing $E$ produces $B$. By the Ampère-Maxwell law (Section 8.2, Exercise 1), a changing electric field acts as a displacement current and so produces a magnetic field circling around it, at points a little further out from the charge than the electric-field change itself.

Step 2: changing $B$ produces $E$. This newly created magnetic field is ALSO changing in time (since it grew from nothing as the disturbance arrived). By Faraday's law of electromagnetic induction, a changing magnetic field induces an electric field at points further out still.

The chain repeats, indefinitely. This newly induced electric field is itself changing, so it triggers another magnetic field further out (step 1 again), which triggers another electric field further out again (step 2 again), and so on without end. Each pair of fields regenerates the next pair a little further from the source, so the whole disturbance keeps recreating itself and steadily advances outward -- a genuinely self-sustaining process that, once started by the oscillating charge, needs no further push to keep travelling, even long after the source charge's own oscillation might have stopped.

Trace the chain step by step: oscillating charge -> changing E -> B via Ampère-Maxwell -> changing B -> E via Faraday -> repeat.

• Describing only ONE step of the chain (e.g. only 'the charge creates a field') without showing how the fields keep REGENERATING each other further out.
• Forgetting that BOTH Faraday's law and the Ampère-Maxwell law are needed together for the chain to work -- either alone is not enough.