Atoms themselves have three main types of sub-particles, protons, neutrons and electrons.
Fig.
1Helium atom
Fig.
2 Helium nucleus
In each atom, the number of protons, which have a positive charge = the number of electrons, which have a negative charge. The number of neutrons is about the same as the number of protons, but does not have to be the same.
There are about 105 different kinds of atoms, or elements, ranging from Hydrogen, with one proton and one electron, through to elements like Lawrencium with 103 of each.
The protons and neutrons are found
in the nucleus, the electrons orbit the nucleus. Thus the nucleus has a
positive charge.
The electrons orbit the nucleus
in layers or levels, according to a fairly complex pattern
In metals, there are only 1-3 electrons in the outermost levels, and since these are a long way from the nucleus, they are not attracted very much by their own nucleus, and are just as likely to be attracted by the nucleus of another atom.
Metals can be thought of being made up of the nuclei and all but the outermost electrons, (which form positive ions,) surrounded by a sea of randomly moving electrons, as for example, in copper.
Metals like copper will conduct an electric current because these electrons are free to move. If one end of the block is made positive, and the other negative, the elctrons will be attracted to the positive end, and repelled by the negative end. Mteals are said to be good conductors of electricity. If there is a continuous circuit, and a source of energy, the electrons will move around the circuit until the supply of energy is exhausted, or until the circuit is broken.
- As the electrons move around the circuit, they are able to transfer their energy to components such as heaters, which convert the electrical energy to other forms, eg. heat and light energy. The energy source could be a dry cell, or a power supply, or a solar cell.
- The energy supplied to the electrons by the energy source = the energy converted to other forms by the components. If the potential difference across a component of a circuit is large enough to be measured, then this component is said to have a resistance, or to be a resistor. Resistors are used in many ways. Light bulb filaments and heating elements are resistors. The volume dial or slide on your Walkman is a variable resistor, or rheostat.