Harvey51 wrote:
Perhaps the mysterious part is how current works. In the wire, free electrons push on each other kind of like cars on a road. If there is a blockage as in an open switch or an opposing voltage push back at the other end, the electrons near that end are stopped like cars at a red light or crashing into stationary vehicles. The stationary electrons push back on those behind via their electric force (like charges repell), bringing the movement of electrons to a stop in the whole length of wire just as happens to cars on a road.
The fluid/particle analogy is useful as a teaching tool for simple approximations like Ohm's or Kirchhoff's, but as with most simple analogies it is wrong to assume that is what actually happens.
The power cannot just 'stop' at the end; that would violate the conservation of mass-energy. The power has to go somewhere. If there is a wire then when too much power for the load to accept gets to the end of the circuit the power that is not absorbed is 'reflected' back towards the source. The reverse wave then limits how much power can continue to flow to the amount that can be accepted at the load. If all power is reflected by the load (as with an open circuit) then the reverse wave cancels out the incoming wave and no net power is transferred.
If you still want to consider the electron movement model as valid consider the numbers:
Based on the measured electron speeds in copper and at realistic current densities it would take hours for your light bulb to turn on after you throw the wall switch. See a sample calculation here
Calculation of electron 'drift' velocity in a copper wire.If electrons were pushing each other it would be faster, but still far longer than anything you ever see. That delay doesn't happen does it....? The power transfer is at very close to the speed of light. It is not electrons moving nor pushing each other that causes the transfer of power. The electric field 'drags' them behind the wave, it's a result and not a cause of the power transfer. Wave theory is way too complex for this forum, but I'm just throwing it out anyway.
