122 Electricity & Electronics A gas, like argon or helium, is heated by solar energy and reaches a temperature in excess of 2,000°F. At this temperature, the gas ionizes. Th e ionized gas is forced through tubing and passed through a magnetic fi eld. Th e magnetic fi eld is produced by winding conductors into a coil around a pipe and then energizing the coil with a small amount of direct current. As the gas passes through the magnetic fi eld, the ions are collected on two conductive plates. Th e negative plate is referred to as the cathode, and the positive plate is referred to as the anode. Th e terms anode and cathode are used throughout the study of electronics and are directly associated with the polarity described above. Th is type of power is in limited production in Middle Eastern countries. Using the sun to produce this type of energy is relatively cheap, but unfortunately not constantly available. 7.2.6 Electricity from Magnetism A common source of electrical energy is the dynamo or generator. Generators prove that magnetism can produce electricity. A generator is a rotating machine that converts mechanical energy into electrical energy, Figure 7-26. Th is source of electricity requires detailed study. Chapter 12, Generators, is devoted to generators, generator types, and controls. SECTION 7.2 REVIEW Answer the following questions using information in this section. 1. Th e _____ produces electricity from light. A. photovoltaic cell B. photoresistive cell C. thermocouple D. None of the above. 2. True or False? When two dissimilar metals in contact with each other are heated, a potential diff erence develops between the metals. 3. Creating electricity by the mechanical distortion of a crystal is known as the _____ eff ect. A. piezoelectric B. photovoltaic C. pyrometer D. polarized 4. True or False? In a fuel cell, there is no heat loss due to chemical reactions. 5. An ionized gas passes through a magnetic fi eld and produces electricity. Th is form of electrical production is made by a(n) _____ device. A. CMOS B. ARRL C. MHD D. DIP 6. A generator is a _____ machine that converts mechanical energy into electrical energy A. oscillating B. rotating C. static D. stationary William Potter/Shutterstock.com Figure 7-26. Rotating copper wires inside a magnetic fi eld will produce electricity. + - Anode plate Ionized gas Cathode plate Coil for magnetic field Output voltage Goodheart-Willcox Publisher Figure 7-25. MHD converter. An ionized gas vapor passes through a magnetic fi eld. The two plates (anode and cathode) collect the ions and pass them to the outside to provide electric power. Copyright Goodheart-Willcox Co., Inc.