Ch01.pptx

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Safety, Basic Electricity, and Ohm’s Law
Section 1

Atomic Structure
Unit 1

Objectives
• After studying this unit, you should be able to:
• List the three principal parts of an atom
• State the law of charges
• Discuss centripetal force
• Discuss the differences between conductors and insulators

Preview
• Electricity
• Driving force that provides most of the power for the
industrialized world
• Electric sources
• Direct current (DC): unidirectional
• Alternating current (AC): bidirectional

Early History of Electricity
• 2500 years ago: Greeks
• First to discover electricity
• Amber could be charged
• Called amber elektron
• Early 1600s: William Gilbert
• Discovered other materials could be charged
• Electriks: could be charged
• Nonelektriks: could not be charged

Early History of Electricity (Cont’d)
• 300 years ago: Charles DuFay
• Charged glass would repel some charged objects and
attract others
• Repulsion
• Attraction

FIGURE 1–1 List of charged materials.

FIGURE 1–2 Unlike charges attract and like charges repel.

Atoms
• Basic building blocks of the universe
• Matter: combination of atoms
• Element: substance that cannot be chemically divided into
simpler substances
• Principal parts of an atom
• Proton: positive charge
• Electron: negative charge
• Neutron: no charge

FIGURE 1–3 Water can exist in three states, depending on temperature and pressure.

Atoms (Cont'd)
• Table of elements
• Lists natural and artificial elements
• Refer to Figure 1-4
• Nucleus of an atom
• Formed by neutrons and protons combining
• Atomic number of an element
• Same as the number of protons in the nucleus

Atoms (Cont'd)
FIGURE 1–4 Table of elements.

FIGURE 1–6 Helium contains two protons, two neutrons, and two electrons.

FIGURE 1–7 The lines of force extend outward.

FIGURE1–9 The lines of force come inward.

The Law of Charges
Figure 1–10 Unlike charges attract and like charges repel.

FIGURE 1–11 Unlike charges attract each other.

FIGURE 1–12 Like charges repel each other.

Structure of the Atom
• Bohr’s model of the atom
• Electrons exist in specific
orbits around the nucleus
FIGURE 1–13 Bohr’s model of the
atom proposed that electrons orbit
the nucleus in much the same way
that planets orbit the Sun.

Electron Orbits
• Electron orbit of an atom
• Contains a set number of
electrons
• Form a shell around the
nucleus
FIGURE 1–14 Electron orbits.

FIGURE 1–15 Electrons orbit the nucleus in a circular fashion.

Valence Electrons
• Located in the outer shell
of an atom
• Valence shell: outer shell
of an atom
FIGURE 1–16 The electrons
located in the outer orbit of an
atom are valence electrons.

FIGURE 1–17 A copper atom contains 29 electrons and has one valence electron.

Electron Flow
• Electrical current: the flow of electrons
• Bump theory
• Current flow occurs when an electron from one atom knocks
electrons of another atom out of orbit
• Striking electron may settle into orbit
• Electron that was struck moves off to strike another

FIGURE 1–18 An electron of one atom knocks an electron of another atom out of orbit.

FIGURE 1–19 The energy of the cue ball is given to the ball being struck.

FIGURE 1–20 The energy of the striking electron is divided.

FIGURE 1–21 The energy of the cue ball is divided between the two other balls.

Insulators
• Materials containing
seven or eight valence
electrons
• Resist the flow of
electricity
• Examples: rubber, plastic,
glass, and wood
FIGURE 1–24 The energy of the striking
electron is divided among the eight electrons.

Semiconductors
• Materials that are neither good conductors nor good
insulators
• Contain four valence electrons
• When heated, their resistance decreases
• Common materials: silicon and germanium

FIGURE 1–25 Semiconductors contain four valence electrons.

Molecules
• Smallest part of a
compound
• Compound example:
water
FIGURE 1–26 A water molecule.

Methods of Producing Electricity
• Six basic methods:
• Magnetism
• Chemical action
• Pressure
• Heat
• Friction
• Light
• Involves the use of photons (massless particles of pure energy)

Electrical Effects
• Five basic effects:
• Magnetism
• Chemical reactions
• Pressure
• Heat
• Light

Summary
• Atom: smallest part of an element
• Principal parts
• Protons: positive charge
• Electrons: negative charge
• Neutrons: no charge
• Valence electrons
• Located in the outer orbit of an atom

Summary (Cont'd)
• Conductors
• Materials provide an easy path for electron flow
• Contain one to three valence electrons
• Insulators
• Materials do not provide an easy path for electron flow
• Contain seven or eight valence electrons

Summary (Cont'd)
• Semiconductors
• Contain four valence electrons
• Used in construction of all solid-state devices
• Molecule
• Smallest part of a compound
• Six basic methods for producing electricity
• Magnetism, chemical action, light, heat, pressure, and
friction

Summary (Cont'd)
• Five basic effects that can be caused by electricity
• Magnetism, chemical reactions, light, heat, and pressure
• Photon: massless particle of pure energy
• Can be produced when electrons move from one energy
level to another

Ch01.pptx

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