# Electricity

In physics, electrical phenomena can be described by the fundamental concept of electric charge: it is a property of matter that can be quantified. There are two types of charge: we call one kind of charge positive and the other negative. Through experiment, we find that like-charged objects repel and opposite-charged objects attract.

Hence, we find that there is a force between these charges that is directly proportional to the magnitude of the charge of the objects and inversely proportional to distance between them. If one object has a certain charge we will call q1, and another has charge q2, then we can express the force from q1 on q2 by:

F=(1/(4πε0))*(q1*q2)/(r2)

Where r is the distance between the charges, and ε0 is a universal constant. See Physical constants.

The unit of charge is called a Coulomb.

Note that this formula, called Coulomb's Law is only fully accurate when the charges are static or moving slowly. When charges start moving quickly, the Electric field undergoes a transformation described by Einstein's Theory of Relativity, and Magnetic fields are produced that effect the amount of force on q1 and q2.

In electrical engineering, a positive current is a current flowing from a positive voltage to a negative voltage.

Natural forms of electricity: lightning.

Humans use electricity. Electricity travels on conductors and is stopped by insulators. Some electrical devices that use the properties of electricty are called electronic devices

Many animals are sensitivie to electric fields, some (eg sharks) more than others (eg people). A few generate their own electric fields, such as the electric eel.