what is coulomb?

[Jawad_13]

why we say that 1C is the charge on 6.25*10^18 electrons but not as the charge of electron?

[TonyV]

from the back of my memory - Coulomb is to do with currnt flow I think

[vascop]

Coulomb is a measure of charge, and is defined as a current flow of 1 amp for 1 second.
See here: http://en.wikipedia.org/wiki/Coulomb

[vascop]

So to answer your question the number you quote must be the number of electrons that 1 amp for 1 second represents,

[TonyV]

Vas - thought charge was measured in Volts and flow in Amps

[chakka35]

No, TonyV. e.m.f. and potential difference are measured in volts. It is, if you like, the electrical pressure that drives a charge (measured in coulombs) through a conductor. The rate of flow of the charge (current) is measured in amps.

Thus one coulomb flowing in one second represents one amp, from which it follows that the amount of charge passed by a current of one amp in one second is one coulomb.

[TonyV]

ok chak - stand corrected - was a physic lesson a long time ago - when we told that that + is really - with regard to electron flow

[chakka35]

You were told correctly, TonyV, though that's really not relevant to this.

I have maintained for years that we should have acknowledged throughout science and in all text-books that electric current flows from negative to positive and not vice-versa.

Too late now. The time to have done it was when transistors came to the fore. We explain the operation of a transistor (the basis of modern micro-electronics) by following the flow of electrons. Then, having finished that explanation, we say 'Forget all that. Now assume that everything flows the other way." Quite wrong:it is electrons that flow one way, not positive ions flowing the other. And quite stupid, but we're lumbered with it.