For a clear picture of electric charge go to an informative website with interactive pictures that will quickly show you pictures that will help give you a better idea of what an electric charge is:
http://230nsc1.phy-astr.gsu.edu/hbase/hf鈥?/a>
then click on ';Electricity and Magnetism'; button,
then ';electric charge'; button and scroll down to a description of conventional electric current that we will discuss later.
You can then click anyplace on the interactive page to get an explanations of the many new ideas in this chapter. You will find this very helpful to have a picture of some of these abstract and complicated concepts.
The electrons found ';orbiting'; the atoms in the universe have various physical properties. Last semester we studied the property of mass and the (gravitational) forces between all masses. This semester we will study the electron's property called ';electric charge'; and the (electrical) forces between all electric charges. Unfortunately we cannot see electric charge the way we can see masses. There are two kinds of charge, negative and positive. The electric charge on an electron is very small and it is NEGATIVE: -1.6(10)-19 Coulombs. The protons found at the center of atoms have the same amount of charge as the electron except it is a POSITIVE electric charge: +1.6(10)-19 Coulombs. We will find later that two charges of opposite sign attract each other and two charges of similar sign repel each other.
If an object has the same amount of positive and negative charge the NET CHARGE on the object is the sum of the two kinds of charge and adds to zero, and we say the object is electrically neutral. So if an object has a number of protons equal to the number of electrons its net charge is zero. (All atoms have a net charge of zero, but ions can have a positive or negative charge depending on whether they have more protons or electrons.) Since the electrons are more mobile than the protons (which are buried in the nucleus of the atom) we transfer elections to a neutral object to make it have a net negative charge. When we do that the neutral object from which we transferred the electrons becomes negatively charged. Note that the total electric charge of the two bodies together does not change - this is known as the conservation of charge. We cannot create or destroy electric charge, we simply transfer charges (electrons) from one object to another to change the NET charge of objects.
The ancient Greeks discovered that electric charge could be transferred between two objects by rubbing them together. In the diagram below, rubbing plastic and fur together results in electrons from the fur being rubbed off onto the plastic, leaving the fur positively charged and the plastic negatively charged. When glass and silk are rubbed together which one has the electrons rubbed off?
