Chapter 10 Fundamentals of Electricity

Introduction This chapter covers the following topics: Matter, elements, and compounds A closer look at atoms Current Voltage Resistance

Matter, Elements, and Compounds Everything can be broken down into elements or compounds Matter –Anything that occupies space and has weight Element –Basic building block of nature

Matter, Elements, and Compounds (cont’d.) Molecule –Smallest part of a compound that still retains properties of the compound Atom –Smallest part of an element that still retains properties of the element

Matter, Elements, and Compounds (cont’d.) Compounds –Chemical combination of two or more elements Mixtures –Physical combinations of elements and compounds –Examples: air, salt water

Matter, Elements, and Compounds (cont’d.) Atom made of protons, neutrons, and electrons –Protons and neutrons form nucleus –Electrons orbit the nucleus Electrons orbit in shells –Shells at various distances from the nucleus

Matter, Elements, and Compounds (cont’d.) Current –Movement of free electrons –Electrons become free when released from outermost shell Voltage –External force needed to create current

Matter, Elements, and Compounds (cont’d.) Resistance –Opposition to the flow of current

Figure 10-1 A compound is the chemical combination of two or more elements. A molecule is the chemical combination of two or more atoms. This example is water (H 2 O) and salt (NaCl). © 2014 Cengage Learning.

A Closer Look at Atoms Atoms of different elements differ from each other Protons are positively charged Neutrons have no charge Electrons are negatively charged Atomic number –Number of protons in atom’s nucleus

A Closer Look at Atoms (cont’d.) Atomic weight : Mass of the atom Determined by number of protons and neutrons in the atom’s nucleus Mass of an electron is insignificantly small

Figure 10-2 Parts of an atom. © 2014 Cengage Learning.

Figure 10-3 The electrons are held in shells around the nucleus. © 2014 Cengage Learning.

Figure 10-4 The number of electrons each shell can accommodate. © 2014 Cengage Learning.

A Closer Look at Atoms (cont’d.) Valence shell –Outer shell –Number of electrons in the valence shell is called the valence The farther the valence shell is located from the nucleus: –The less attraction the nucleus has on each valence electron

A Closer Look at Atoms (cont’d.) Conductivity of an atom depends on its valence band –The greater number of electrons in valence shell, the less it conducts Valence shell electrons can gain energy –With sufficient energy, they can leave the atom and become free electrons

A Closer Look at Atoms (cont’d.) Conductors –Materials containing a large number of free electrons Insulators –Absorb valence electrons from other atoms to fill their valence shells Eliminates free electrons

Figure 10-5 Conductivity of various metals. © 2014 Cengage Learning.

Figure 10-6 Copper has a valence of 1. © 2014 Cengage Learning.

A Closer Look at Atoms (cont’d.) Semiconductors –Neither good conductors nor insulators –Can be altered to function as conductor or insulator –Examples of semiconductor materials: silicon and germanium Ionization –Process of gaining or losing electrons

Current Signified by symbol I Sum of charges of moving electrons past a given point One coulomb –The charge of 6.24 x electrons added together

Current (cont’d.) One ampere –One coulomb of charge moving past a single point in one second

Voltage Current flows between two ends of a conductor: –When one end is positively charged and the other negatively charged Potential –Source that creates the charge difference

Voltage (cont’d.) Voltage : Force that moves electrons in a circuit Also called electromotive force (emf) Represented by symbol E Unit is the volt (V)

Figure 10-8 Electrons flow in a circuit due to difference in potential © 2014 Cengage Learning.

Resistance Opposition to the flow of electrons –Caused by atoms that do not readily give up electrons Every material offers some resistance –Conductors have low resistance –Insulators have high resistance Resistance is measured in ohms (Ω)