ELECTRICITY and MAGNETISM

 Several thousand years ago, the ancient Greeks observed that a substance called amber attracted bits of lightweight material, such as feathers or straw.  AMBER is a good electric insulator, so it easily holds electric charge, they were actually experimenting with static electricity when they rubbed amber. The Greek word for amber is elektron.  Other people, including the ancient Greek and Chinese, knew of another substance that could attract things. It was a black rock called lodestone or magnetic.

 Girolamo Cardano an Italian Mathematician in 1551, realized that the attracting effects of amber and of magnetite must be different. Cardano was the first to note the difference between electricity and magnetism.  In 1600, the English physician William Gilbert reported that such materials as glass, sulfur and wax behaved like amber. When rubbed with cloth, they too attracted light objects. Gilbert called these as electrics. He studied the behavior of electrics and concluded that the effects must be due to some kinds of fluid.  In 1730, the French scientist Charles Dufany found that the charge pieces of glass attracted amberlike substances but repelled other glasslike substances. Dufany decided to have 2 Kinds of Electricity. He called one vitreous and the other resinous. He thought of them as two kinds of “electric fluid.”

 The American scientist and statesman Benjamin Franklin began to experiment with electricity in Franklin thought that there is only one electric fluid. He theorized that objects with too much fluid would repel each other but they will attract if there are less fluid. His ideas explained how opposite charges cancel each other out when they come in contact.  He used the term positiive for what he thought was an excess of fluid and he used the negative for a deficiency fluid. He did not know that electricity is not a fluid. Rather, electricity is associated with the charges of electrons and protons.

 In 1767, the English scientist Joseph Priestley described the mathematical law that shows how attraction weakens as the distance between oppositely charged objects increases.  In 1785, the French scientist Charles Augustin de Coulomb confirmed Priestley’s law. Coulomb showed that the law also held true for the repulsive force between objects with the same charge.  In 1771, Luigi Galvan, found that the leg of a recently killed frog would twitch when touched with two different metals at the same time.  In the late 1790’s Alessandro Volta showed that chemical action occurs in a moist material in a contact with two different metals. Volta gathered pairs of disks, consisting of one silver and one zinc disk. Then Volta constructed the first battery called a voltaic pale.

 The Danish physicist Hans C. Oersted found that an electric current flowing near a compass needle would cause the needle to move. He is the first to show a definite connectin between electricity and magnetism.  During 1820, Andre Ampere discovered the relationship between currents and magnetic fields called Ampere’s Law, it is one of the basic laws of electromagnetism.  The physicist James Maxwell combined all the known laws covering electricity and magnetism into a single set of 4 equations.  In later 1880’s Heinrich Hertz showed how to generate and detect radio waves, transmitted electromagnetic waves and satellite communication.

 The Irish physicist G. Stoney believed that electric current was actually the movement of extremely small electriically charged particles called electrons.  In the late 1880’s, scientists discovered that electrons can be dislodged from metal surface in a vacuum tube. Vacuum tube contains electrodes with wires that extended through the glass.  In 1947, Bardeen, Brattain and Shockley invented the transistor. Transistors do the same job as vacuum tubees but they are smaller and more durable and they use less energy.

 Most of the electric energy we use comes from power pplants that burn fossil fuels, such as coal, oil and natural gas. Some electric energy comes from nuclear and hydroelectric plants.  Many people are concerned that the earth’s supply of fossil fuel is limited and will someday run out. Another problem is that the present methods of generation electric energy may harm the environment.  Many scientists hope that new electric devices will actually help curb the growing demand for electric energy. Computers, for example, can control the lights, air conditioning and heating the buildings to reduce energy use. Compact fluorescent lamps, using miniature electronic circuits, provide the same light as ordinary light bulbs but use only one-fifth as much electric energy.

 The electric charges can be redistributed by induction. If a negatively charged object is placed near a surface that conducts charges, the electrons on the sphere will move away from the object. On the other hand, the positive charges on the sphere will be attracted toward the oppositely charged object.  An electroscope is two thin gold leaves hanging from a stem in an insulated jar and lid. Insulators are materials, such as cloth, some plastics, glass and oil that tend to prevent charges from moving. This is an instrument which can confirm when you have built up static charge.