1
$\begingroup$

Suppose I have a conducting wire attached to a battery and it carries some current. As a result there also exists a magnetic field around the wire. If I then detach the wire ends from the battery, the current ceases to flow and subsequently, there is a varying magnetic field around the conductor which acts as a source to create an electric field in the surrounding. This varying electric field in turn produces a magnetic field and the cycle will continue. My questions are as follows,

(1) Is the above reasoning correct? Does this actually happen?

(2) If yes then from where did the energy now stored in the electromagnetic field come from?

(3) Also, will this energy propagate outwards in space or will it remain localized in the surroundings?

$\endgroup$
  • $\begingroup$ a) yes b) It is stored in the current, i.e. kinetic energy of electrons c) The emitted electromagnetic field will propagate outwards. This is roughly how antennas work $\endgroup$ – Jannick Aug 22 '18 at 13:51
  • $\begingroup$ @Jannick How exactly will the field/energy propagate outwards? $\endgroup$ – Rutwik Aug 22 '18 at 14:01
1
$\begingroup$

Yes, your reasoning is correct.

The energy in the wave is the energy that was momentaneuously stored in the wire.

The direction in which the wave propagates will vary depending on the wire. If you have a straight wire with $l$ >> $\lambda$, one could approximate that the wave will radiate outwards from the wire equal in all directions (of course this does not hold for the edges of the wire, but hey, it's an approximation)

$\endgroup$
  • $\begingroup$ Would very high currents and sudden switching off cause visible radiation too? $\endgroup$ – Rutwik Aug 22 '18 at 16:21
  • 1
    $\begingroup$ Your wavelength is very long, like in the radio spectrum and not it the visible spectrum. If you turn on an AM radio you will likely hear a static noise when you do your experiment. $\endgroup$ – PhysicsDave Aug 22 '18 at 17:02
  • $\begingroup$ @Rutwik Visible radiation would be the case if the wavelength was in the visiblespectrum, but unles your wires length is of the order of nanometers, that will not likely. If you've a few centimers, you'll create radiowaves, possible microwaves. $\endgroup$ – DakkVader Aug 23 '18 at 9:18

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.