2019 Cengage CHAPTER 2 BASIC ELECTRICITY INTRODUCTION Most
© 2019 Cengage
CHAPTER 2 BASIC ELECTRICITY INTRODUCTION • Most control systems used in heating, cooling, and refrigeration use electrical energy to maintain temperature • Industry technicians must understand basic principles of electricity to perform their jobs • The study of electricity begins with a discussion of atomic structure © 2019 Cengage
CHAPTER 2 BASIC ELECTRICITY Atomic Theory • Key terms • Matter • Composed of fundamental substances • Elements • Atom • Smallest particle of an element • Molecule • Smallest particle of a substance © 2019 Cengage
CHAPTER 2 BASIC ELECTRICITY Atomic Theory • Atomic structure • • • Nucleus Electrons Protons Neutrons Hydrogen atom © 2019 Cengage
CHAPTER 2 BASIC ELECTRICITY Atomic Theory • Compounds • Created when elements (and atoms) are combined • Form a chemical union • Results in a new substance © 2019 Cengage
CHAPTER 2 BASIC ELECTRICITY Positive and Negative Charges • Charge • Neutral atoms have equal numbers of protons and electrons • When electrons are gained or lost, atoms become charged • Atoms can lose a few electrons for short periods • Atoms can acquire additional electrons © 2019 Cengage
CHAPTER 2 BASIC ELECTRICITY Positive and Negative Charges • Electricity • An atom that has lost or gain an electron is considered unstable • Law of electric charges • Like charges repel • Unlike charges attract © 2019 Cengage
CHAPTER 2 BASIC ELECTRICITY Flow of Electrons • Static electricity • Oldest method of moving electrons • Permanently displaces an electron from an atom • When charges are equalized, flow stops • Usually caused by friction © 2019 Cengage
CHAPTER 2 BASIC ELECTRICITY Flow of Electrons • Electricity through chemical means • Battery produces electron flow by electron flow • Dry cell batteries • Storage batteries • A chemical reaction causes transfer of electrons between two electrodes © 2019 Cengage
CHAPTER 2 BASIC ELECTRICITY Flow of Electrons • Electricity through magnetism • Conductor cuts through a magnetic field • Examples: alternator, generator, and transformer • Used to supply electricity to consumers • Flow of electrons produces magnetism • Thermal energy, which in turn is used to cause heat • Movement © 2019 Cengage
CHAPTER 2 BASIC ELECTRICITY Conductors and Insulators • Conductor • Free electrons available • Can transmit electricity or electrons • Insulator • Does not easily give up or take on electrons • Retards flow of electrons © 2019 Cengage
CHAPTER 2 BASIC ELECTRICITY Electrical Potential • Electric pressure • Electrons will flow as long as electric pressure is applied • Terms • Voltage • Potential difference • Electromotive force © 2019 Cengage
CHAPTER 2 BASIC ELECTRICITY Electrical Potential • Field of force • Attraction between to dissimilarly charged objects • Electromotive force • Dry cell battery • Alternating current generator © 2019 Cengage
CHAPTER 2 BASIC ELECTRICITY Current Flow • Current • Electron flow in an electric circuit • Bolt of lightning • Static electricity • Electron flow from a generator • Types of current • Direct current • Alternating current © 2019 Cengage
CHAPTER 2 BASIC ELECTRICITY Current Flow • Ampere • Used to measure current in an electric circuit • amount of current required to flow through a resistance of 1 ohm with a pressure of 1 volt • Measured with an ammeter © 2019 Cengage
CHAPTER 2 BASIC ELECTRICITY Resistance • Electric devices • All have a resistance depending on two factors • Size • Purpose • Deviation from value in components can mean the device is faulty • Specified value • Estimated value © 2019 Cengage
CHAPTER 2 BASIC ELECTRICITY Electric Power and Energy • Electric power • Rate at which electrons do work • Measured in watts (W) • Formula • Electric power = voltage × amperage • Multiply by a power factor to obtain power consumed © 2019 Cengage
CHAPTER 2 BASIC ELECTRICITY Electric Power and Energy • Conversion figures • 1 horsepower = 746 watts • 1 watt = 3. 41 Btu/hour © 2019 Cengage
CHAPTER 2 BASIC ELECTRICITY Electric Power and Energy • Electric energy • Rate at which electric power is being used at a specific time • Measured in watthours (Wh) © 2019 Cengage
CHAPTER 2 BASIC ELECTRICITY Electric Power and Energy • Seasonal energy efficiency ration (SEER) • Btu output of the equipment divided by the power input with a seasonal adjustment • Used by all air-conditioning manufacturers for their equipment • Set by the Air-Conditioning, Heating, and Refrigeration Institute © 2019 Cengage
CHAPTER 2 BASIC ELECTRICITY Ohm’s Law • Overview • Relationship among the current, electromotive force, and resistance • Greater the current and the greater the resistance, the lesser the current • Current is equal to the electromotive force divided by the resistance © 2019 Cengage
CHAPTER 2 BASIC ELECTRICITY Calculating Electric Power • Formula for electric power • P = IE • Two other formulas • P = E 2/R • P = I 2 R © 2019 Cengage
CHAPTER 2 BASIC ELECTRICITY SUMMARY • Everything is composed of matter • An atom is composed of a nucleus and electrons • Electrons can be made to flow by friction, chemicals, and magnetism • The number of electrons flowing in an electric circuit is called the current flow • Ohm's law gives the relationship among current, electromotive force, and resistance © 2019 Cengage
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