**Ask a monkey a physics question thread**

[OngBonga]

Well I correctly guessed it would be 1/c, but I don't really know why, other than to say that I know what's not happening is electrons are speeding around the circuit. What I don't get is where this 1/c takes into account the distance between the switch and the bulb. The time I think it should take for the bulb to come on is the time it would take a photon to travel in a straight line from switch to bulb. That depends on the distance between the two. but 1/c seconds is just a fixed 3x10^-9 seconds.

But c isn't just 300000000, it's 300000000 m/s. c is a measure of distance over time, not just a plain number.

I think when he says 1/c that he's saying the bulb comes on at the speed of light in a straight line between switch and bulb, not the time it takes light to complete the circuit. I think 1/c is the speed of light, written as time rather than distance.

[OngBonga]

I knew I'd seen something else on this subject...

[OngBonga]

Basically, charge and energy are not the same thing. Both are flowing when there's a complete electric circuit, but while the charge moves with the current. along the wire, the energy flows perpendicular to the charge, into the electromagnetic field.

The complete circuit means electrons begin to flow. Moving charge creates a magnetic field. Energy flows in this magnetic field. Energy is not flowing along the wire. It's flowing radially out of the battery, perpendicular to the wire, and into the device. The energy flows through space. The current merely creates the electromagnetic conditions needed for the flow of energy to be able to happen through space. The device takes energy out of the EM field, and the battery replenishes it. When the battery has no power left, electrons stop moving, and the EM field collapses. Energy flow ceases.

It's all a bit crazy though, not remotely analogous to water flow.