Current

An electric current is a flow of electric charge. Electric charge flows when there is voltage present across a conductor.

The direction of the current is from the positive terminal of the cell, around the circuit to the negative terminal. This is a scientific convention: the direction

 of current is from positive to negative and hence the current may be referred to as conventional current. 

In a typical metal such as copper or silver, one electron from each atom breaks free to become a conduction electron. The atom remains as a positively charged ion. 

The current is present at all points in the circuit as soon as the circuit completed. We do not have to wait for charge to travel around from the cell.

Sometimes a current is due to both positive and negative charges; for example when charged particles flow through a solution. A solution which conducts is called an electrolyte and it contains both positive and negative ions. These move in opposite directions when the solution is connected to a cell.

Charge

When charged particles flow past a point in circuit, we say that there is a current in the circuit. Electrical current is measured in amperes (A). 

Charge is measured in coulombs (C). 

One coulomb is the amount of charge which flows past a point in a circuit in a time of 1s when the current is 1A.

The amount of charge flowing past a point is given by the following relationship: 

Q=I x t 

Where Q is the amount of charge (C), t is time (in s) and I is current (in A)

Blog entry by Saif Rehman