For a long time electricity and magnetism were thought to be separate forces. In the 19th century Maxwell demonstrated that they were interrelated phenomena then Einstein proved with the Special Theory of Relativity that they are aspects of one unified phenomenon.
The core of the relationship is that a changing magnetic field produces an electric field and conversely, a changing electric field produces a magnetic field.
The electric force is already familiar to us: it is the force that is created by the movement of electrons from negatively charged atoms to positively charged atoms. The current is the flow of this moving charge.
> Every constituent of matter has an electric charge with a value that can be positive, negative, or zero. For example, electrons are negatively charged, and atomic nuclei are positively charged. Most bulk matter has an equal amount of positive and negative charge and thus has zero net charge.
The properties of charge as the embodiment of a law of nature are defined in [Coulomb's Laws](/Electronics/Physics_of_electricity/Coulombs_Laws.md).
### Charge conservation
In addition to Coulomb's Laws is the notion of **charge conservation**, another fundamental law of nature.
This basically means that the overall charge of an isolated system cannot change. If you have a system that has a charge equillibrium and you introduce disequillibrium by adding a postively charged particle, a particle with a negative charge of the same magnitude will be created at the same time, thus the overall charge is conserved. (This is due to the way that radiation interacts with matter.)
A field is a property of space. It means that a physical quantity is assigned to every point in space. This quantity has a numerical value and may vary over time.
There are different types of field. The electric field is an instance of a **vector field**. With vector fields there is more than one number for each point in space:
> The value of the electric field at a point in space equals the fore that would be exerted on a unit charge at that poisition in state.
Every charged object sets up an electric field in the surrounding space. A second charge “feels” the presence of this field. The second charge is either attracted toward the initial charge or repelled from it, depending on the signs of the charges. Of course, since the second charge also has an electric field, the first charge feels its presence and is either attracted or repelled by the second charge too. The electric field from a charge is directed away from the charge when the charge is positive and toward the charge when it is negative.
