1.4 ELECTRICITY, MAGNETISM, MOTORS AND 25 The best magnetic materials are iron and its compounds, while most metals such as copper, gold, silver and aluminium are nonmagnetic. The studies leading to the discovery of electromagnetism were done in several steps by different scientists. H. C. rsted discovered that electric current gives rise to magnetism. M. Faraday discovered that magnetism could induce electric currents, and J.C. Maxwell put the whole thing together in a unified theory of electromagnetism. ONLINE RESOURCES Electromagnetic waves ELECTROMAGNETISM Electricity and electric fields Electricity is the phenomenon associated with either stationary or moving electric charges. The source of the electric charge could be an electron, which has a negative charge, a proton, which has a positive charge, an ion, or any larger body that has an imbalance of positive and negative charge. Positive and negative charges attract each other, while charges of the same sign repel each other, thanks to the electric field that surrounds them. Magnetism and magnetic fields Everyone must have experienced that, if we hold two magnets, they can either stick together very strongly, or push each other away. This is due to the polarities of magnets, N (north) and S (south); like electric charges, two identical poles repel each other, while two opposite ones attract each other. Magnets can also attract other objects, made of magnetic materials . The force that surrounds magnets and attracts, or repels, objects or other magnets is called a magnetic field. Electromagnetism Electricity and magnetism had been studied separately for a long time. However, these two phenomena are strictly related to each other. When current flows through a conductor, such as copper wire, a magnetic field is generated around it. The field strength and direction depend upon the amount of current flowing and its flowing direction along the wire. By wrapping the wire around in a loop to form a coil, we obtain a solenoid; by adding more windings of wire to a solenoid, it is possible to increase the strength of a magnetic field. A magnetic field, on the other side, can generate an electric current; in fact, if a magnet is moved towards or away from a solenoid, the changing magnetic field induces a current in the wire. The direction of the current depends on the direction of the movement . Applications of electromagnetism The discovery of electromagnetism gave a strong impulse to the invention of the most commonly used devices in everyday life such as electric motors, generators and transformers. loop: anello winding: avvolgimento to wrap: avvolgere 58 elecTriciTy aND iTs aPPlicaTioNs Elettronica-Informatica.indb 58 25/01/24 16:07