105 Chapter 7 Sources of Electricity E very student knows the story of Benjamin Franklin and his kite. For centuries before Franklin, scientists and philosophers had observed lightning. It was through the experimentation and research of Franklin that the relationship between lightning and static electricity was confi rmed. What is electricity and where does it come from? Years before the discovery of the electron theory by J. J. Th omson, it was suggested by Franklin that electricity consisted of many tiny particles, or electric charges. He further theorized that electrical charges were created by the distribution of electrical particles in nature. OBJECTIVES After studying this chapter, you will be able to: ■ List the six basic sources of electricity. ■ Explain the chemical action that creates electricity in various types of cells. ■ Defi ne polarization. ■ Explain the differences between primary cells and secondary cells. ■ Distinguish between series and parallel connections in batteries. ■ Calculate the outputs of batteries connected in series and parallel. ■ Discuss proper use of a hydrometer and explain its use. ■ Calculate the theoretical capacity of a battery. KEY TERMS amalgamation ampere-hours (Ah) anode battery capacity cathode depolarizing agent dry cell electrode electrolyte fuel cell generator hydrometer intercalation local action magnetohydrodynamic (MHD) photoresistive cell photovoltaic cell piezoelectric effect polarization primary cell pyrometer secondary cell specifi c gravity thermocouple thermopile voltaic cell