# Coulomb - count of particles or unit of charge ?

Discussion in 'Physics' started by RipClaw, Oct 9, 2008.

1. ### RipClaw Thread Starter New Member

Oct 9, 2008
3
0
I am a bit confused with what coulomb means.

Does coulomb mean:
A count of the number particles who lost their peace, and now known as charged.

OR

unit of charge itself & particle count does not matter.

I am also confused with the following circular definition.
Elementary Charge = 1.602176487(40) × 10^–19 coulombs
Coulomb = 6.241 509 629 152 65 × 10^+18 elementary charges

ωτ∫ ?

What is the fun ? If you multiply them both, you get 1

2. ### Papabravo Expert

Feb 24, 2006
10,338
1,850
The answer is that it is both. The definition is NOT circular, it is an equivalence relation. They are reciprocals of each other, and when we multiply reciprocals together we get, ceteris paribas, 1 !!

3. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
A Coulomb is a measure of charge as defined by the accumulation of 6.24 x 10^18 elementary charges. So the charge on that many electrons make up a Coulomb.

4. ### RiJoRI Well-Known Member

Aug 15, 2007
536
26
Of course, this brings up the question, who counted those 6 1/4 bazillon charges??

--Rich

5. ### triggernum5 Active Member

May 4, 2008
216
0
Did Coulomb actually define that number, or was it derived later via charge/mass relationship of an electron, and the correlation of voltage and work/energy..
Remember 1Watt = 1V*A = 1J/s = 1N*m/s, and we already had proper defined newtons, meters, seconds, and volts..

6. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
6
The name was chosen to honor Coulomb, not derived by him. It is the charge accumulated in one second by a current of one Ampere.

7. ### triggernum5 Active Member

May 4, 2008
216
0
Didn't think Coulomb had the technology to pull that off..

8. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
6
I've learned the elementary charge was first calculated by Robert Milikan in 1909 using a oil drops, a microscope, x-rays, and electrified plates. I still have not turned up the name of the person who counted the charges per second per amp, though.

9. ### ZAIZAI New Member

Oct 14, 2008
3
0
The oil drop experiment is actually very neat. It is described in numerous text books, I am sure, Nuclear Physics by Irving Kaplan is one of them.

Simple experiment together with some mindbogling theory (mathematics) and you kan figure out the charge of one electron...

Yes everyone knows the charge is minus one, but prove it!

10. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
The charge on an electron is not divisible. As it is a unit charge, setting it equal to -1 is simply a matter of definition. No proof needed.

11. ### Dave Retired Moderator

Nov 17, 2003
6,960
145
It stems from the SI-definition of the Ampere:

Ref. http://physics.nist.gov/Pubs/SP330/sp330.pdf

This definition comes from work by André-Marie Ampère on his Force Law. Note that the Ampere is a base unit.

We know from Millikan's experiment the value of the elementary charge. And Charles-Augustin de Coulomb defined the Coulomb to be:

Or perhaps more logically in context of this discussion an ampere is one coulomb of charge going past a given point in the duration of one second.

Therefore you can empirically arrive at the conclusion 1C = 6.24150962915265 x10^18 elementary charges.

Dave