In course we will describe electric current is a flow of electric charge - moving electrons in a wire -through a conductive medium. It is also true to say that electrical currents may also exist in liquids and gases and, taking things a step further, in a vacuum, a beam of ions or electrons may be formed as well.

Any materials consist of atoms. An atom is constructed of protons, electrons and neutrons. Protons carry a positive electrical charge, electrons carry a negative electrical charge and neutrons carry no electrical charge at all. The protons and neutrons cluster together in the central part of the atom, called the nucleus, and the electrons 'orbit' the nucleus. An atom containing an equal number of protons and electrons is electrically neutral, otherwise it is positively (lack of electrons) or negatively (surplus of the electrons) charged.

In modern physics, an electrical charge is an intrinsic property of matter, such as mass.

The most important features are follow:

- There are two types of electrically charged objects: positive (+) and negative (-). Oppositely-charged object will attract, while like charge will repel each other.

- The charge of a body is sum of the charges of its constituent particles. If it contains the same amount of each type of charge, then the body is neutral and its electrical charge will be zero.

- The electric charge is conserved: The charge is neither created nor destroyed; its total value remains constant.

- The electrical charge can move through some materials that are known as conductors. Those materials that do no allow the electrical charge to flow inside them are known as insulators (non-conductors).

- The charges of free-standing particles are integer multiples of the elementary charge e; we say that electric charge is quantized.

Proton and electron charges are identical in terms of absolute level. The value is:

e= 1,602 x 10 ^-19 C

Conductors are type of materials in which electric charges move freely. On the other hand insulators do not allow the free movement of electric charges although support static charges.

Electric current is a flow of electric charge through a conductive medium: conductors or semiconductors. Therefore if we know the charge that flows/tunnels through a section of the conductor in each unit of time we are able to determine its current.

A brief introduction to "electricity" (http://www.youtube.com/watch?v=EJeAuQ7pkpc )

 

An electric current is a flow of electric charge Q through an electrical conductor in each unit of time:

The standard units of measurement for electrical current is Ampere = Coulomb/sec - amperes (A) or milliamperes (mA). One milliampere is 1/1000 of an ampere.

One coulomb (1 C) is the charge that flows each second through a section of a conductor travelled by one ampere current.

When current (I ) is constant and the electrons always flow in the same direction, then the current is direct.