Quoted from EvanDickson:Pinball-ish question.
Ok, so a transistor has a gate, a source, and a drain. I get that when the gate is closed, electricity can flow from the source to the drain.
But I don't get how simply applying voltage to a single pin can close the gate. I'd understand if the power flowing from gate to a ground created a magnetic field and moved something. But I'm not sure how applying a low voltage to just a point, without somewhere for that voltage to flow to, can cause work to happen.
I guess I'll throw my hat in the ring.
The simple answer is the voltage on the gate of the FET creates a charge. It's this charge that turns the transistor on or off. No gate current is needed for this action to occur. Since no current flows through the gate the gate doesn't draw any power, as power requires both voltage and current (P=VxI).
Kind of like if you put a charge on a balloon by rubbing it on your head, your hair will move towards the balloon without any current flowing between your hair and the balloon (no power required).
A bipolar transistor (base, emitter, collector) is functionally similar to a FET, but it's base does require current flow and it's internal operation is very different than the FET.