The other day, a friend and I were looking at a simple resistor-capacitor-inductor circuit. As we were looking at the circuit, he mentioned that the capacitors and inductors "talked" to each other through the air. From this, I assume he meant that the capacitors and inductors were exchanging EMF waves, and that it was an essential part of how these circuits operated.

I was surprised by this because I didn't remember learning about this in my circuits class, but it made some sense because I figured every electronic device is emitting some sort of EMF wave. I just always assumed these were of minor importance to the circuit.

My question is how do these circuit elements communicate with each other in simple RCL circuits? Is it primarily through the voltage/current local to the wires, or are there important EMF considerations.

To clarify, I understand that at some level, the voltage/current in the wires is being controlled through EMF waves since that is how the charge of an electron is communicated to near by electrons. I am referring to EMF waves here to be over macroscopic distances (between circuit elements).

  • $\begingroup$ There is a good discussion on feynmanlectures.caltech.edu/II_27.html. ex: it is shown how the energy into a charging capacitor comes not by the wire, but from outside. But it is not EM waves, it is a changing EM field. $\endgroup$ Jun 4, 2020 at 23:47
  • $\begingroup$ But is the effect the capacitor is having on the EM field having a measurable effect on the rest of the circuit elements? In other words, if I completely shielded the capacitor from the remainder of the circuit, would the behavior of the circuit be greatly effected? $\endgroup$ Jun 5, 2020 at 0:15

1 Answer 1


One form of this interaction which is real and has consequences is called radiated electromagnetic interference. This happens when the circuits are carrying high frequency signals, under which conditions a simple piece of wire in the circuit or a trace on a PC board becomes an antenna, broadcasting EM waves. When those waves strike other circuit elements, they can induce unwanted flows of electricity in them, with the potential to completely upset the operation of the circuit.


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