We’ve been taught that electricity is a very fast flowing phenomenon, we switch on a button and the tube-light flashes on, the fan starts to rotate, a motor runs at its full speed in just milliseconds but that’s not the truth, an electron inside a conductor flows even slower than a snail or even a turtle. You don’t believe me? After this, you might.
The speed at which an electron moves inside a conductor is called its drift velocity and as a matter of fact a thing which is not taught to us that it is one of the slowest phenomena in this whole world.
Let us look it by the math,
I= N x A x v x q
I= current-1 A
N= no of electrons in copper wire- 8.5*10ˆ+22
v= drift velocity of the electron
q= charge- 1.6*10ˆ-19
Q * e * R^2 * pi
on solving it for a current of 1A about 100V for 100W bulb we get Drift velocity as
0.0023 cm/sec or 8.4 cm/hour.
But if electrons move so slowly, how can a switch turn on a lamp instantaneously? Think of a tube filled with marbles: if you add a marble at one end, a marble will come out the other end at almost the same instant, even though each marble didn’t move that far on its own. Similarly, a copper wire contains lots of electrons (8.5×10^28 per cubic meter, to be exact) moving an electron at each second produces a lot of electrons flowing through the wire making it a kind of avalanche at a particular second.
Thereby, even though a single electron moves very slowly but, together in a group even a slow value gives us such great amount of current. Electrons in metals do not hold still. They wiggle around constantly even when there is zero electric current. However, this movement is not really a flow, it is more like a vibration.
[Picture: By Jürgen Schoner – Originally uploaded on the German Wikipedia as “Weinbergschnecke 01.jpg”. Own work of Jürgen Schoner., CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=201455%5D