120 Electricity & Electronics place when the gases combine with the potassium hydroxide. Th e ionization will continue as long as the two gases are supplied to the electrolyte. Typically, the cell develops only 1.23 volts. However, when used in the space program, these cells have been designed to develop over 2 kW of energy. Th e theoretical effi ciency of the fuel cell is 100%. Th ere is no heat loss due to chemical reactions. Th e only by-product of the fuel cell is water, resulting in virtually no pollution. 7.2.5 Magnetohydrodynamic Power Generation Electricity is generated when an ionized gas is passed through a magnetic fi eld. Th is method of producing electricity is called magnetohydrodynamic (MHD). Figure 7-25 is an illustration of the MHD converter. Building a Thermocouple In this experiment you will demonstrate and construct a simple thermocouple. MATERIALS ■ 1 piece of copper wire ■ 1 piece of iron wire ■ 1 pack of matches ■ 1 multimeter PROCEDURE 1. Twist one of the copper wires together with one end of the iron wire. 2. Connect the leads of the multimeter to the opposite two ends of the copper and iron wire. Set the meter to read voltage. (Be sure to observe the proper measuring technique.) 3. Light a match and heat the junction of the two wires. 4. Observe the results on the meter. Explain what you have just observed. Could you use materials other than copper and iron? E x p e r i m e n t 7 - 3 Hydrogen Catalyst Hot water Hydrogen Water Anode Cathode Battery Load Charge controller Oxygen Oxygen Hydrogen Fuel Cells H 2 O Studio BKK/Shutterstock.com Figure 7-24. A fuel cell is a device that converts chemical from a fuel into electricity through chemical reaction of positively charged hydrogen ions with oxygen or another oxidizing agent. Copyright Goodheart-Willcox Co., Inc.