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82 2.20. James Prescott Joule (1818-89) The English (1) physicist James Prescott Joule is famous for his experiments with heat. He discovered that the (2) various forms of energy - mechanical, electrical, and (3) heat - are basically the same and that one form can be changed into another. Joule's (4) research was so significant that his name was given to a (5) unit of work or energy, the joule (j). Joule did not have any formal academic training or an academic post. However, he worked with some of the (6) leading scientists of the time, including the English chemist John Dalton (1766-1844), and the Scottish physicist Lord Kelvin (1824- 1907). Unit 3. Electrical Engineering 3.1. What is Electricity? Electricity is a (1) flow of negative charges called electrons. (Electrons are particles that form a part of all atoms.) These electric charges are (2) measured in units called coulombs. Electricity is a very versatile form of energy that can be (3) converted into many other forms of energy, including light and heat. There are two types of electricity: (4) direct current (DC), which flows in one direction only, and (5) alternating current (AC), which changes direction 60 times per second. 3.2. Making Electricity Almost any form of energy can be (1) converted into electricity. The most common methods of producing electricity are those used in (2) batteries or generators. Power from batteries is (3) generated by converting chemical energy into electrical energy. Most generators convert heat energy (from (4) burning fuel) into electrical energy. Some generators exploit such natural resources as sunlight or wind to (5) obtain electrical energy. 3.3. Static Electricity Unlike (1) current electricity, static electricity does not flow. It is created when an electrically (2) neutral substance loses or gains electrons (negatively charged particles), making it, respectively, positively or negatively charged. You can create static electricity by (3) rubbing a balloon on your clothing. Electrons will (4) move from the clothing to the balloon, making the balloon negatively charged and the clothing positively charged. The resulting static electricity on each will (5) attract small, light objects such as pieces of paper. 3.4. Magnets Magnets are attracted to (1) iron and to any material that contains iron. Magnets have two poles, a (2) north pole and a south pole. Unmagnetized iron and steel have magnetic (3) regions of atoms called domains that are jumbled up and point in lots of different directions. When iron or steel (4) becomes magnetized, the domains become aligned and they all point in the (5) same direction. One end of each domain points toward the magnetic north pole. 3.5. Electromagnetism Electricity and magnetism (1) combine to form one of the fundamental forces of the universe - electromagnetism. The two (2) constantly interact, and the (3) relationship between them is one of the most important in physics. For example, an electric current passing (4) through a wire creates a magnetic field; and if the lines of force around a magnet are (5) cut by a passing object, an electric current will be produced. These, and other such (6) phenomena, form the basis of much of today's technology.