Electricity PDF

of individuals and businesses until power is restored. Electricity is taken for granted until problems occur. People simultaneously rely on electricity and fear it. Most people are afraid of electricity because they know it can cause severe burns, shock, or even death. A thorough knowl- edge can hel...

of individuals and businesses until power is restored. Electricity is taken for granted until problems occur. People simultaneously rely on electricity and fear it. Most people are afraid of electricity because they know it can cause severe burns, shock, or even death. A thorough knowl- edge can help to reduce fear, but remember to never lose respect for electrical energy. The poten- tial for injury or death is very real. A high percentage of heating and cooling service calls are for electrical problems. Understanding how electricity controls and operates heating and cooling equipment is essential for troubleshooting system problems and performing routine repairs. This chapter explains the release of electrical energy by electron movement between atoms. Electromotive force and proper use of voltmeters are described as well. These basic principles lay the foundation for a discussion of electron move- ment and the use of ammeters. Explanations of resistance, Ohm’s Law, and the use of ohmmeters clarify how electrical energy is converted to another form of energy. Watt meters and kilowatt-hour meters as measurements of electrical power are also explained. 23.1.1 Energy Conversion Electricity is a form of energy. Other forms of energy are heat, light, chemical (battery), atomic (power plant), and mechanical (motor). As was discussed in Chapter 9, the First Law of Thermo- dynamics states that energy cannot be destroyed, but it can be converted from one form to another. For example, heat can be used to produce elec- tricity, and electricity can be used to produce light. The reverse is also possible. Electrical appliances and devices convert electrical energy to another form of energy to perform useful tasks. 23.1.2 What Is Electrical Energy? Electricity is a form of energy in which elec- trons move from one atom to another atom. All matter is composed of atoms, the smallest particle of any element. Although atoms are tiny, they are a vast source of potential energy. The center of an atom is called the nucleus. The nucleus contains protons and neutrons. Protons are atomic parti- cles that have a positive charge (+), and neutrons are atomic particles that have no charge (neutral). The atomic number of an element indicates the number of protons in its nucleus. Orbiting around the nucleus are electrons carrying a negative charge (–). The number of orbiting electrons normally equals the number of protons in the nucleus. The positive charges in the nucleus exert a strong magnetic force that holds the negatively charged electrons in orbit around the nucleus. See Figure 23‑1. The simplest atom is the hydrogen atom. It contains one proton and one electron. The proton has a positive charge (+) that exactly balances the negative charge (–) of the electron. Other elements have more than one proton and one electron in their atoms. All electrons possess the same nega- tive charge, while all protons possess an equal posi- tive charge. Their charges are equal and opposite. Hence, electrons and protons neutralize each other. Any stable or electrically balanced atom has an equal number of protons and electrons. A stable atom is said to be neutral (has no charge). An atom can have from one to over 100 elec- trons, depending on the element. Oxygen has an atomic number of 8. Therefore, it has 8 electrons orbiting around the nucleus. Copper has an atomic number of 29. It has 29 electrons. Uranium has an atomic number of 92, so it has 92 electrons. Electrons orbit around the nucleus much like the planets orbit around the sun. Electrons travel in pathways called shells, and an atom can have as many as seven shells. Electrons traveling in shells located close to the nucleus are more tightly bound to the nucleus than those in the outer