In fact, electrical energy always flows through the empty space surrounding the wires. The circuit is just there as a guide, but the actual energy-flow surrounds the metal and is not inside the wires. From the viewpoint of a physicist, it’s more suprising that EM energy needs wires, than it’s suprising that EM energy can flow right through plastic.
There are three common ways to communicate AC or DC electrical energy from place to place:
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Use a pair of wires (where the metal guides the energy-flow)
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Use a pair of capacitors (the energy flows through the gap between metal plates)
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Use a pair of inductors (the energy flows through the gap between coils of wire.)
Number one is how circuits work. Number three is how transformers work (although the coils are normally spaced close together, so we don’t usually think of transformers as being transmission lines.
Number two is rarely used, but it’s part of the way that all radio antennas function. Sometimes in science classrooms the teacher will demonstrate that a “tesla coil” can light up a flourescent tube held in the hand with no wires connected. That’s an example of number two above.
Most people have never heard that electrical energy flows NEXT TO wires rather than inside them. This topic is covered in engineering courses on EM waves and waveguide theory, and in physics courses on E and M. But in textbooks below college level, this fact is never mentioned.
I think it’s unknown because the math is misleading. The simple math lets us know the energy flow in a circuit, but the math has some powerful implications which are not true…
To calculate the amount of energy being transferred across an electric circuit, we can measure the voltage and the current, then multiply them together. For some reason, textbook authors then assume that the current is the electrical energy. And since the current is inside the wires, the energy is inside there too. Wrong. The electrical energy doesn’t flow inside the metal. Instead it is contained in the magnetic and electrostatic fields surrounding the wire circuit. Unfortunately it’s very hard to measure watts by measuring those fields directly. So instead, we measure the magnetic field indirectly by measuring electric current. And we measure the electric field indirectly by measuring the charge-imbalance on two parts of the circuit (with a further layer of indirect measurement, since we measure VOLTS rather than measuring charge or field strength.)
Multiply volts times amps and you know the energy flow rate; the “power.” Your voltmeter or amp meter function by touching the metal of the circuit. But the energy flow is not inside the metal. It’s not inside the cord leading to your floor lamp. Instead it is in the space surrounding the cord. Very weird. Very fascinating, in my opinion, but then I just love to think about simple useful ideas that, for some reason, never filter down to public school classes and never get spread out into everyday technical knowledge.
