# How electrons move so fast in a electric circuit?

Whenever we switch on a bulb......it takes almost no time to glow up.....But we know that the atoms of a solid are tightly packed and there is a very little space between them. So how the electrons travel through them irrespective of so much blockages in the conductor???

• there's nothing special about the electron near your fingertips compared to the one at the lightbulb; either one can light it up Commented May 16, 2015 at 17:36
• "We know that the atoms of a solid are tightly packed and there is a very little space between them..." > Actually, the space between atoms is huge when you compare it to how very tiny the nucleus of an atom is. Commented May 16, 2015 at 21:38
• This post has two questions: the explicit "how do electrons flow through the wire" and the implicit "how does electricity work?" It's disappointing that the only answers to the explicit question are downvoted, and the upvoted answers only address the implicit question, and appear to be about direct current rather than alternating current.
– user5174
Commented May 17, 2015 at 3:35

The electrons themselves don't move all that fast. The wave energy is the part that moves quickly.

Picture it this way.

You have 500 meters of pipe, with a small hole at the other end. The pipe is full of water and you increase the pressure at your end. Water will flow out the other end immediately. This is the electrical energy (pressure) and the copper(water).

Now add some dye to the water and note how long it takes for the coloured water to come out the hole. The dye represents the new electrons, and they take noticeable time to move through the system. Pressure moves immediately.

(ok, in this case pressure moves at the speed of sound in water)

• in this case pressure moves at the speed of sound in water. What's the equivalent limiter for the movement of electrons in a circuit? Commented May 16, 2015 at 14:02
• @MasonWheeler The conduction electrons are accelerated by the mostly-uniform electric field in the conductor; what limits their speed is the mean free paths between collisions with the fixed atoms on the lattice.
– rob
Commented May 16, 2015 at 15:30
• @MasonWheeler: Electricity moves through conductors at some significantly-large fraction of the speed of light in a vacuum. See en.wikipedia.org/wiki/Speed_of_electricity Commented May 16, 2015 at 17:59
• @Ejay No analogy is perfect. The pipe has a small hole at the end; cover that with your finger, if you want to keep the water inside. Standard assumptions apply: the water is incompressible, the walls of the pipe perfecly rigid, you are in an inertial frame, it is not a leap-year, the horse running alongside the pipe is light and spherical, etc. Commented May 16, 2015 at 21:36
• @CortAmmon The 'speed of electrons' referred to in this answer is their average drift speed, not their instantaneous speed. Yes, electrons are travelling really, really fast, but that's mostly just orbiting nuclei. Their drift velocity through the medium is much slower than that. At least that's my understanding. Admittedly, it has been a few years since my chemistry/physics classes. Commented May 17, 2015 at 6:32

In fact, electron's speed is not so fast that light bulb glows up immediately. It is the electromagnetic field which travels in the circuit at near the speed of light that is resposible for it.

After turn on the light, electron only acquires a little speed in addition its thermal speed. The thermal speed of electron can be estimated by $mv^2/2\approx k_BT/2$, where $k_B$ is the Boltzmann constant and $T$ is the absolute temperature and nearly 300 K. So the thermal speed is about 67.4 km/s.

In the electric field inside the circuit, the distance the electron travels freely before hitting the nucleus is estimated to about 300 nm in copper. If the voltage is 110 V, the speed increases by 86 m/s. In fact, the increase is the upper bound, because I assume the voltage change in 300 nm is 110 V, which is not true. Voltage changes over a much longer distance.

So you see, the increase in speed of electron is only about 86 m/s. The draft speed of electron is not really hight (compared to thermal speed).

Electrons can sneak pass all the atoms because of their wave function. They behave like waves not like particles. In short, because of quantum mechanics. In a periodic assembly of atoms like metallic solid they should not feel any resistance when moving through but because it is not perfectly periodic they feel aperiodic potential and this is why they scatter. They scatter on vibrations of atoms! And, they move really fast but they have no definite direction. When you apply electric field to that metal, signal travels through the wire and all electrons practicly at once start moving in one direction, but slowly. This is known as drift speed. While they still move chaotically and with great speed, they slowly drift in one definite direction and it is this speed that that adds up to the original and still existing chaotic motion that is related to current and our harvesting energy of moving electrons.

• Downvotes are intersting...what for? Simple question, simple answer...i believe it was enough. Commented May 17, 2015 at 9:48
• this answer is OK as far as I see. I think it is the "sneak" that brought the downvotes. There are people fast-reading and filling in blanks as they see fit. Commented May 17, 2015 at 10:49
• Why? Its a nice description and it is a way in which a scientist Bloch who invented Bloch functions described his wonder... Commented May 18, 2015 at 15:06

You might be asking how metal is such an efficient conductor.

Some of the electrons move freely as a fluid. They are not locked in place around the atoms, and don't need "room" in the classical sense.