Does an electromagnetic field persist if no current is flowing?

Does an electromagnetic field persist if no current is flowing?

• A. Yes, it persists due to stored energy.
• B. It remains for a short time after current stops.
• C. It exists only in static conditions.
• D. No, it collapses when current ceases to flow.

Answer: (D)

When an electromagnetic field exists, it can be sustained by energy stored in the field itself, not only by ongoing current. Electric fields arise from charges and can persist with no current if charges remain separated (as in a capacitor). Magnetic fields come from currents, but the energy stored in that magnetic field can keep the field present for a short time after the current drops, until that energy is dissipated or radiated away. And in free space, electromagnetic waves carry fields without any conducting current, so the field can persist as radiation even without a current in a wire. So, the field can remain after current stops because energy is stored in the field, and it only fades as that stored energy leaks away. The statement that it collapses immediately with no current ignores this stored-energy aspect and the possibility of radiation.

When an electromagnetic field exists, it can be sustained by energy stored in the field itself, not only by ongoing current. Electric fields arise from charges and can persist with no current if charges remain separated (as in a capacitor). Magnetic fields come from currents, but the energy stored in that magnetic field can keep the field present for a short time after the current drops, until that energy is dissipated or radiated away. And in free space, electromagnetic waves carry fields without any conducting current, so the field can persist as radiation even without a current in a wire.

So, the field can remain after current stops because energy is stored in the field, and it only fades as that stored energy leaks away. The statement that it collapses immediately with no current ignores this stored-energy aspect and the possibility of radiation.