Charge and current
An electric current is a flow of charged particles.
In metal conductors the charged particles are free electrons.
The electrons are free to move from one ion to another and a net flow of these electrons in one direction is an electric current.
A source of energy, such as a cell or battery, is required to make the free electrons move in one direction.
Charge
Electrons are negatively charged particles and they transfer electrical energy from a cell, through conducting wires, as an electric current.
Charge is measured in coulombs, C.
The charge of an electron is 1.6 x 10-19 C.
In other words, it takes 6,250,000,000,000,000,000 electrons to make up 1 coulomb of charge.
A coulomb of charge is just a very large group of electrons.
The relationship between current I and quantity of charge Q
An electric current is a flow of charged particles.
The size of an electric current is the rate of flow of charge.
Current I = \(\frac{\text{quantity of charge Q}}{\text{time taken t}}\)
I = \(\frac{\text{Q}}{\text{t}}\)
This is often remembered as:
Quantity of charge Q = current I x time t
Q = It
Where:
Q = quantity of charge in coulombs, C
I = current in amperes, A
t = time in seconds, s
| I = \(\frac{\text{Q}}{\text{t}}\) | I = Q Ă· t |
| Q = It | Q = I x t |
| t = \(\frac{\text{Q}}{\text{I}}\) | t = Q Ă· I |
| I = \(\frac{\text{Q}}{\text{t}}\) |
| I = Q Ă· t |
| Q = It |
| Q = I x t |
| t = \(\frac{\text{Q}}{\text{I}}\) |
| t = Q Ă· I |
One ampere is the current that flows when one coulomb of charge passes a point in a circuit in one second.