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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 (H2O) 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 1018 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)