Hello I'm Daven Hiskey and you are watching
the Today I Found Out Youtube channel.
In the video today we're looking at the surprisingly
slow speed of electricity.
Let's get started.
You may be surprised to learn that electrons
flow through a typical copper wire much slower
than a turtle walks.
Each wire that conducts a flow of electrons,
producing usable electric current, is composed
of billions of atoms.
To move along it, the electrons have to traverse
these atoms, randomly zig-zagging their way
as they do, resulting in the net flow rate,
called “drift velocity,” in a given direction
being quite slow.
How slow exactly?
To calculate it, we use this formula: I = n*A*v*Q
or v = I/(n*A*Q)
I is the current, n is the number of electrons
per cubic meter, A is the cross-section of
the wire, Q is the charge of an electron and
v is the drift velocity of the electrons.
Since the number of electrons in a copper
wire (n) is 8.5 * 10^28 per m^3, and the charge
of an electron (Q) is 1.6 * 10^-19 coulombs,
if we also know the cross sectional area and
the current, we can calculate the electrons’
drift velocity.
For example, suppose you have a current of
14 amps and a copper wire with a cross section
of 3 * 10^-6 m^2.
Plug in all the numbers and you get that the
electrons are moving at a speed of 3.4 * 10^-4
m/s – or about a whopping one-third of a
millimeter per second.
To put it in values that are easier to conceptualize,
this works out to about 1.2 meters or 4.1
feet per hour- a rate about 195 times slower
than the average box turtle, which can cover
about 800 feet in that same amount of time.
So how is it that something that makes a turtle
look like the Road Runner can more or less
instantaneously turn on a light across a room?
Chain reaction.
The atoms in the wire are crammed together
cheek to jowl, which, while it makes the going
slow, also has the electrons more or less
abutting one another.
When the switch is turned on, thanks to the
electrical potential difference created by
the generator, a force is created to move
the electrons, with each pushing its neighbor,
which in turn pushes its neighbor and so on
all the way through the wire.
So, while no electrons zoom through the wire
to turn on the light as you might have previously
thought, it ends up seeming like that is what’s
happening.
This is not unlike how when you turn on your
faucet, water instantly comes out despite
the fact that your water source might be many
miles away.
