How can there be a wide range of current flow?

[Tim Barber]

I am trying to expand my knowledge of electricity. I always thought that electricity and light move at one constant speed. If this is true, then how can there be a wide range of current flow? I think of current flow as (electrons/second). If this is not true, then what are the limits of speed of electron flow (low and high) through a conductor? 

 

[exchemist]

19 minutes ago, Tim Barber said:

 

I am trying to expand my knowledge of electricity. I always thought that electricity and light move at one constant speed. If this is true, then how can there be a wide range of current flow? I think of current flow as (electrons/second). If this is not true, then what are the limits of speed of electron flow (low and high) through a conductor? 

 

In an electric current, the electrons move through the conductor very slowly, not at the speed of light. As I understand it, what moves fast through a conductor is any signal, i.e. any change to the rate of flow at one end propagates very fast to the other end, because the electrons in between can be though of as essentially incompressible. 

Since current is a measure of the charge passing a given point per unit time, e.g, amps = Coulombs/sec, a greater current can be achieved by more electrons moving, as well as by a greater speed of motion.

But some of the physicists here may be able to explain better than I can.

 

[Tim Barber]

2 minutes ago, exchemist said:

In an electric current, the electrons move through the conductor very slowly, not at the speed of light. As I understand it, what moves fast through a conductor is any signal, i.e. any change to the rate of flow at one end propagates very fast to the other end, because the electrons in between can be though of as essentially incompressible. 

Since current is a measure of the charge passing a given point per unit time, e.g, amps = Coulombs/sec, a greater current can be achieved by more electrons moving, as well as by a greater speed of motion.

But some of the physicists here may be able to explain better than I can.

 

What I would like to see is numbers for RATE of electron flow. e.g. # of electrons / second passing through a conductor (air in the case of lightning) vs. the number of electrons / second passing through the wires that power you home. The same or not? How many electrons/second are passing a fixed point in each conductor? 

 

[exchemist]

45 minutes ago, Tim Barber said:

What I would like to see is numbers for RATE of electron flow. e.g. # of electrons / second passing through a conductor (air in the case of lightning) vs. the number of electrons / second passing through the wires that power you home. The same or not? How many electrons/second are passing a fixed point in each conductor? 

 

Oh that's easy. There are ~6.25 x 10¹⁸ electrons in one Coulomb of electric charge and 1 amp = 1 Coulomb/sec.  

You can find estimates on the internet for the current in amps in a lightning discharge. Bear in mind that, as current is a rate of flow of charge, you can get very high currents without necessarily transferring enormous amounts of charge, if that current only flows for a fraction of a second. 

Edited July 10, 2022 by exchemist

[John Cuthber]

1 hour ago, Tim Barber said:

What I would like to see is numbers for RATE of electron flow. e.g. # of electrons / second passing through a conductor (air in the case of lightning) vs. the number of electrons / second passing through the wires that power you home. The same or not? How many electrons/second are passing a fixed point in each conductor? 

Lightning involves currents of something like 10,000 amps (it's very variable)

The circuit breakers at your fuse box probably limit the current your house can draw to less than (about) 100 amps. So the lightning only draws the same as about 100 houses (if they were all "maxed out") probably more like 1000 houses most of the time.

However, if you want to compare power, you have to take the voltage into account, and lightning has a much higher voltage- something like a million times higher than that supplied to your house. A lightning strike would power about a billion households. But not for long.

 

If you try to measure very very small currents say, less than 10^-15 of an amp, you don't get a steady current.
The effect of each electron passing becomes "noticeable".
If the average current is only 1000 electrons per second, then the variability is quite large- about 32 electrons per second on average.

This is one source of "noise" in electronic systems.