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If current is the rate of flow of electrons past a point. Let's say a wire is full of electrons, and of course they pretty much are already going the speed of light, minus friction. What would increasing the voltage do?

You can't go faster than the speed of light, and you can't increase the rate of electrons because no more fit in the tube. I am just curious what this would look like. I feel like I am missing a key concept.

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    \$\begingroup\$ Electrons don't move at the speed of light. They are not massless particles and they can not move at the speed of light. In a wire, they (on average) typically don't move any faster than you can walk. \$\endgroup\$
    – The Photon
    Commented Mar 31, 2020 at 1:06
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    \$\begingroup\$ Saying electrons move at the speed of light is like saying wind blows at the speed of sound. An electromagnetic wave in conductors moves at relativistic speeds (not actually the speed of light but large fractions of it), but the electrons do not. Do not mistake movement of the medium for a wave travelling through the medium. \$\endgroup\$
    – DKNguyen
    Commented Mar 31, 2020 at 1:15
  • \$\begingroup\$ Electrons move like the marbles in a Newton's Cradle, pushing each other. The speed at which the first movement of an electron to propagates until the last one is the speed of light minus a few percents. \$\endgroup\$
    – Fredled
    Commented Mar 31, 2020 at 11:09
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    \$\begingroup\$ The folks who run the Pacific Intertie say "the electrons we started pushing from Oregon in 1970 still haven't reached L.A. yet". \$\endgroup\$
    – Harper - Reinstate Monica
    Commented Mar 31, 2020 at 19:07

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The speed of the electrons have nothing to do with the "height" of the voltage.

Static electricity is a prime example. You can have a 4MV charge on insulated object and none of the electrons are moving.

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When you apply voltage to a circuit, it's not the electrons which travel at the speed of light but the information "voltage source is connected to wire" is what travels at the speed of light. And this information travels as voltage and current waves across the wire. These waves are described by the Telegrapher's Equation.
Once these waves settle a constant current flows through the wire proportional to the applied voltage. Why current increases with voltage?
Increasing the voltage means there is more electric field in the wire and the drift velocity of electrons is proportional to applied electric field. $$v_d = \mu E$$ The constant of proportionality is known as the electron mobility. And, more velocity means more current.
There are two caveats which I would like to address for completeness:

  1. The Telegrapher's Equation which describe the EM waves as equivalent voltage and current waves is valid only for Transverse Electromagnetic (TEM) Mode of wave transmission.
  2. At high enough electric fields, the drift velocity of the electrons start to approach their thermal velocity and drift velocity starts to saturate. This is because all the energy gets lost in collisions with the atoms. And the current does not increase even after increasing the voltage.
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Water can move faster in a pipe with higher pressure but electric charges and electrons can't move faster with voltage. Voltage increases the concentration of electrical charge and allows to move them with less friction instead of increasing its speed. By contrast, you can't concentrate water in a pipe with more pressure. Also water doesn't heat the pipe but transmits its pressure to it, causing it to blow if the pressure is too high. Current heats whatever it crosses. The electric energy is therefore converted into heat. Eventually melting the wire if the current is too high. Voltage reduces this heating by allowing more energy to move freely.

500V is like sending a box with 500 balls in it. 5V is sending the same box (same box size and same box weight) with only 5 balls inside. The energy wasted to move 500 balls with 100 boxes will be much higher than with one box.

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  • \$\begingroup\$ I think you are conflating the concepts of voltage and current. The net velocity of the electrons can change, but it changes based on the current (or more precisely, the current density) not the voltage. Current does not "heat whatever it crosses". Voltage does not "reduce this heating". \$\endgroup\$
    – Elliot Alderson
    Commented Mar 31, 2020 at 12:16
  • \$\begingroup\$ I think Fred is trying to say "current heats whatever is passes through" and "power can be transmitted more efficiently at high voltage as current will be reduced and transmission losses will be reduced as a result". The analogy in the opening sentences is broken too: for a constant resistance increasing water pressure increases current; for a constant resistance increasing voltage will increase current; electron drift velocity in a metallic conductor will increase if the cross-sectional area remains the same. \$\endgroup\$
    – Transistor
    Commented Mar 31, 2020 at 12:29
  • \$\begingroup\$ @Elliot Alderson Tell me what current can cross (or "passes through") without heating it (except supraconductors). And for an equal amount of energy, higher voltage requires less current, therefore reducing energy loss through heating. "The velocity of the electrons can change... based on the current, not the voltage." That's exactly what I said. Current is what causes the movement of electrons but the energy is proportional to the voltage potential. The loss of energy through resistance causes a voltage drop. Which means energy is linked to voltage. \$\endgroup\$
    – Fredled
    Commented Mar 31, 2020 at 19:09
  • \$\begingroup\$ Electrons traveling through free space do not cause the vacuum to heat up, and superconductors are indeed another valid example. The energy available can be converted also to light or chemical changes. The correct statement is "current passing through resistance is converted to heat". This matters! Higher voltage means less current only if the delivered power is constant, which you haven't specified. No, current does not cause the movement of electrons, current is the movement of charge. You've mixed up cause and effect for a number of important concepts. \$\endgroup\$
    – Elliot Alderson
    Commented Mar 31, 2020 at 19:20
  • \$\begingroup\$ @Transistor My point is that you can't compare water velocity in a pipe with electron velocity in a cable because the electric energy is not some moving matter but an electromagnetic field. rift velocity is irrelevant (I think) It's important to understand that electricity is not a flow of liquid in a pipe. \$\endgroup\$
    – Fredled
    Commented Mar 31, 2020 at 19:29

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