All atoms contain charged particles of two types. Electrons have a negative charge and can be easily moved between atoms. Protons have a postive charge and cannot move between atoms.
When you use a cloth to rub an insulator such as a balloon or a plastic ruler, electrons are rubbed from one to the other. A negatively charged object has gained electrons. A positively charged object has lost electrons.
If you bring two charged insulators close together, they will exert forces on each other. This is illustrate in the images below.
Two charged rods with the same charge
Two charged rods with different charge
Two rods where only one is charged
An electric current is a movement of charge, so if the charge can move off an insulator, it forms a current.
Examples of charge producing a current
If you rub your feet on some types of carpet, you will build up a charge. When you touch something else, the charge flows from your body and you feel the shock.
Air masses moving past each other in clouds can build up charges. Sometimes there is enough energy to form long sparks. This is lightning.
In conductors, the electrons that carry the negative charges are free to move. The current in an electric circuit is caused by the movement of the charges through the conductors of the circuit.
The symbol for current is \(I\).
The unit that is used to measure current is the ampere\((A)\).