Transcript:

Okay, consider you have a battery with a positive and negative terminal, and you connect some wires from the positive to one side of a light bulb, and from the negative—through a switch—to the other side of the light bulb. Now you make a circuit, and when the switch is turned on, you see the light bulb goes on instantly.

So, do you really think that those electrons are moving at the speed of light through the conductor, through the wire, and that is why the light bulb turns on instantly? Not a chance. The electrons are just diffusing. In fact, in an AC current, those electrons are oscillating only. They're not moving at all. Yet, the light bulb comes on instantly when in your house, even with AC current, you switch on the circuit—meaning you throw the switch.

So what's going on? Turns out it's not the electrons that are diffusing so fast. It has to do with Poynting. It has to do with Maxwell—his equations of electromagnetism—and Poynting's formula for calculating the power flux or the power density.