# Electron flow in a wire [duplicate]

How do electrons that constitute a current flow move in a wire? Some say it's like a wheel.If you give it a push,every part of the wheel moves instantly. Is that what happens to electrons?Do they start moving everywhere in the wire when the circuit is closed? Why? Or is it because electrons bump into each other and the energy travels at the speed of light?

• possible duplicate of Is electricity instantaneous? – Ignacio Vergara Kausel Sep 24 '14 at 12:32
• It's not quite instantaneous, but the change in the electric field in the wire once it's connected (which is what drives the electron motion) will propagate at the speed of light. – johnpaton Sep 24 '14 at 12:37

Under the influence of an applied electric field, electrons in conductors actually do not move very fast, in regards to their bulk flow velocity. For instance, in copper the bulk drift speed of electrons is less than a millimeter per second. However, each electron (specifically, the conduction electrons) has an effective speed of over one million meters per second. The effective speed is a random speed and it turns out to only depend upon the material (e.g., for copper it is ~1.6$\times$10$^{6}$ m/s), neither the temperature nor the applied electric field. The random speed and drift speeds are important for determining the mean free path (~4$\times$10$^{-8}$ m or ~40 nm in copper) and collision rate (~4$\times$10$^{13}$ collisions per second in copper) for conduction electrons.

The short answer is yes, the conduction electrons hit each other (which causes the transfer of information) and while their net drift speed is very low, the rate of communication through the conductor is slightly below the speed of light.

• Voltage is the work done to move a charge from one point to another. They hardly move however.So what is voltage?And resistance? Does it mean that a wire with more resistance make electrons bump slower?Sorry I'm lost. – SMcCK Sep 25 '14 at 7:59
• @SmCcK voltage is kind of like gravitational potential energy. If you apply a voltage difference between two points, a charged particle in that region will accelerate. Resistance (or resistivity) in a material is kind of like friction, in a sense. In a superconductor, for instance, current can flow indefinitely without loss. – honeste_vivere Sep 25 '14 at 11:36
• @SmCcK in short, the collision rate I referred to is dependent upon the electron drift speed whereas their mean free path is dependent upon the random speed of the electrons and the collision rate. You can also think of it this way: $\mathbf{j}$ = $n_{e}$e$V_{drift}$ ~ $\sigma$ $\mathbf{E}$. So yes, the resistivity of a material affects the drift rate and mean free path of electrons. – honeste_vivere Sep 25 '14 at 11:40

As soon as you complete the circuit an electric field travels though the wire. $$E=\frac{V}{x}=\frac{F}{Q}$$ The electric field travels at the speed of light so for wires in use are too small that the electric field will take noticeable time to travel through the wire. As the electric field is constant around the wire and is (almost) instantly there in whole of the wire every electron experiences the same force: $$F=\frac{Ve}{x}$$ Where $e$ is charge on one electron.
Every electron experiences the same force due to electric field not because neighboring electrons bump into them.

If the circuit is closed, one after the other electrons start to move in the chain between the source and the sink approx. with the speed of light. This is because the electrons always feel each over and the signal about the start moves approx. with c.

The same happens in a water pipe too. Try it. Of course you can't measure how fast the signal "open wider the stopcock" come to the end of your pipe. More excited it is if the pipe was heated by the sun and, if you open stopcock, the water flows "instantaneously", but the cooler water comes with delay. Of course take in attention the other answers about the zig-zag-trajectory of the electrons.