The Atom And Electrical Current.

• All matter is made of atoms. Atoms are very small and when placed in a straight line about 8 million will fit into 1mm. 
• Atoms themselves are made up from three particles: electron, proton and neutrons. Electrons and protons have equal but opposite charges; the electron has a negative charge and the proton has a positive charge. 
• The neutron has no charge. Charges behave like magnetic poles in that alike charges repel and unalike charges attract. 
• The protons and neutrons make up the nucleus which is at the centre of the atom and the electrons reside around the outside (figure 1.1). 
• Normally an atom will have equal numbers of electrons and protons so that as a whole the atom has no overall charge. 

•  In solid materials that are conductors the electrons are free to move between atoms. The movement may be random in all directions throughout the conductor however, if the electrons move predominantly in one direction an electric current flows. 
• Since the protons are at the centre of the atom they can not break free, therefore electricity is the flow of negative charge and not the flow of positive charge. 
• Because of these phenomena any region of negative charge is formed by an excess of electrons gathering and a region of positive charge is due to electrons moving away, leaving a deficit. 
• Solid materials, where the electrons are not able to move are insulators and such materials do not conduct electricity. 
• Materials that conduct electricity under certain conditions are called semiconductors. In a piece of metal, a wire for instance, electrons are free to move in any direction. 
• However, as soon as a battery is connected to both ends of the wire the electrons will move towards the positive battery terminal. For every electron that leaves the wire through this terminal, another enters the other end of the wire from the negative terminal; thus the total number of electrons in the wire remains the constant. 
• This flow of electrons from a negative terminal, through the wire, to the positive terminal is called an electric current. For historic reasons, in most circuits electricity is considered to flow from the positive terminal to the negative terminal; in fact for most circuits it does not matter which direction you consider the electricity to flow. 
• When a current flows in a conductor two important things happen:

1. heat is generated,
2. a magnetic field is set up around the conductor.