 # Terms

In the universe, there are four fundamental interactions:

• Strong Interaction
• Electromagnetic Interaction
• Weak Interaction
• Gravitational Interaction

The Electromagnetic Interaction (classical: force) concerns particles (whatever they are) of different charge, a mass-like quantity.

A charged particle with charge Q (a real number) will cause a force F on a charge q (r is the distance between q and Q in space): (whereas is the electric constant).

Or, if you are unhappy with the destination q, the electric field strength E is: The constant factor is just to connect the unit of the electric force to the other SI standard units of measurement. Its value is: Now, in a conductor there are some free electrons which can move from atom to atom and these cause electricity to flow (they do not carry the electricity literally, but they cause a field with causes electricity to flow).

(electrons have charge -e, ).

In any case, if the charge Q moves through a conductor, we say an electric current I is flowing (in analogy to water currents). Likewise as with gravity, we introduce the (electrostatic) potential energy W_{el}: I'm not sure where the minus sign is now...

Or, if you are unhappy with the destination q, the electrostatic potential is: As was the case with gravity, you can choose the zero potential to be anywhere.

If there is a difference in electrostatic potential, this is called a voltage U: In this case, if possible, a current will flow in order to even out the differences until there is no voltage anymore (if possible).

If no current can flow, influence will still happen: the charges within each atom will rearrange in a way so that like-signed charges are as far away from each other and differently-signed charges are as closely together as possible.

## Wire

A wire is an electrical conductor which has little resistance to the current.

Usual materials a wire is made of: copper, silver.