Current and Charge



Charge carriers are a charged particle. Current in a circuit is induced by the flow of these charge carriers. Current is defined as the rate of flow of charged particles in a wire or component.
In a metal the charge carrier is an electron which is free to move around the molecule colliding with each other and positive ions within the metal.
In a salt solution the charge carrier is a ion, an ion is a charged atom or molecule.

Convention of current
Originally before the discovery of electrons it was believed that current flowed from positive to negative within the circuit, when in fact its negative to positive. (This is because electrons are negative being repelled by the negative side and attracted to the positive side of the cell/battery.)

∆Q = I∆T
I x T = Electrons passing a point in used time
1.6x10^-19

Worked example

A) If the charge flow is 50C and the current is 10A what is the time taken for this amount of charge to pass a point in the circuit?

B) How many electrons pass through the circuit in this time?

Answers
A)
Using equation ∆Q = I∆T

Rearrange it to find time, this is done by dividing the entire equation by the value of current.
This will cancel out current from the right side and divide the value of charge on the left side of the equation. This should look like
∆Q = ∆T
I

50C / 10A = 5 seconds

B)
I x T /1.6x10^-19 = electrons passing a point per value of time


10 x 5 / 1.6 x 10 ^ -19 = 3.125 x 10^20