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Coulomb - count of particles or unit of charge ?

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RipClaw

Joined Oct 9, 2008
3
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. :confused:
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 :rolleyes:
 
Papabravo

Papabravo

Joined Feb 24, 2006
22,084
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 !!
 
beenthere

beenthere

Joined Apr 20, 2004
15,819
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.
 
T

triggernum5

Joined May 4, 2008
216
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..
 
thingmaker3

thingmaker3

Joined May 16, 2005
5,083
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.
 
thingmaker3

thingmaker3

Joined May 16, 2005
5,083
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.
 
Z

ZAIZAI

Joined Oct 14, 2008
3
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!
 
beenthere

beenthere

Joined Apr 20, 2004
15,819
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.
 
D

Dave

Joined Nov 17, 2003
6,969
thingmaker3 said:
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.
Click to expand...
It stems from the SI-definition of the Ampere:

The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross section, and placed 1 meter apart in vacuum, would produce between these conductors a force equal to 2 × 10−7 newton per meter of length.
Click to expand...
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:

[the] amount of electric charge transported by a current of 1 ampere in 1 second
Click to expand...
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
 
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