Chapter 2 Basic Electricity

Objectives Upon completion of this course, you will be able to: –Briefly explain the atomic theory and is relationship to physical objects and electron flow –Explain the flow of electrons and how it is accomplished –Explain electrical potential, current flow, and resistance and how they are measured

Objectives (cont’d.) –Explain electrical power and how it is measured –Explain Ohm’s law –Calculate the potential, current, and resistance of an electrical circuit using Ohm’s law –Calculate the electrical power of a circuit and the Btu/hour rating of an electrical resistance heater

Key Terms Alternating current Ampere Atom Compound Conductor Current Direct current Electric energy Electric power Electric pressure Electricity Electrode Electrolyte Electron

Key Terms (cont’d.) Element Field of force Free electron Insulator Kilowatthour Law of electric charges Matter Molecule Neutron Nucleus Ohm Ohm’s law Power factor Proton

Key Terms (cont’d.) Resistance Seasonal energy efficiency ratio (SEER) Static electricity Volt Voltage/Potential difference/ Electromotive force Watt

Introduction Electrical energy –Used to maintain desired temperature Control systems used in the heating, cooling, and refrigeration industry Basic principles of electricity –Must be understood by technicians To correct problems

Atomic Theory Key terms: –Matter: substance of which a physical object is composed Composed of fundamental substances (i.e., elements) –Atom: smallest particle of an element that can exist alone or in combination –Molecule: smallest particle of a substance that has the properties of that substance

Atomic Theory (cont’d.) Atom structure: –Nucleus: made up of protons and neutrons –Electrons: orbit the nucleus –Protons: positive charge –Electrons: negative charge –Hydrogen atom: simplest atom One proton and one electron

Atomic Theory (cont’d.) Figure 2.1 Atomic structure of a water molecule (one atom of oxygen and two atoms of hydrogen). (Delmar/Cengage Learning)

Positive and Negative Charges Atoms can lose a few electrons for short periods –Electrons in outer orbits of some materials can be easily knocked out of their orbits (i.e., free electrons) Conductors: materials with free electrons Atoms can acquire additional electrons –Become negatively charged

Positive and Negative Charges (cont’d.) Electricity: –One atom is charged and there is an unlike charge in another atom Electrons can flow between the two Law of electric charges: –Like charges repel and unlike charges attract

Positive and Negative Charges (cont’d.) Figure 2.2 Like charges repel and unlike charges attract each other. (Delmar/Cengage Learning)

Flow of Electrons Accomplished by several means: –Friction: produces static electricity –Chemical: produces electricity in a battery –Magnetic (induction): produces electricity in a generator –Other methods are also used

Static Electricity Oldest method of moving electrons –Permanently displaces an electron from an atom –Prolonged or steady flow of current is not possible –When charges are equalized, flow stops –Usually caused by friction

Electricity Through Chemical Means Battery produces electron flow by a chemical reaction –Causes transfer of electrons between two electrodes Figure 2.3 Construction of a dry cell battery. (Delmar/Cengage Learning)

Electricity Through Magnetism Conductor cuts through a magnetic field –Causes a displacement of electrons Examples: alternator, generator, and transformer Used to supply electricity to consumers –Flow of electrons produces magnetism Used to cause movement, or thermal energy, which in turn is used to cause heat

Conductors and Insulators Conductor: material that has free electrons available –Can transmit electricity or electrons Example: most metals Insulator: material that does not easily give up or take on electrons –Retards flow of electrons Example: glass, rubber, and asbestos

Electric Potential Important terms: –Voltage Volt, ampere, and ohm –Potential difference –Electromotive force –Field of force –Electric pressure

Electric Potential (cont’d.) Figure 2.6 A dry cell battery supplying electric potential (voltage) to an electric circuit. (Delmar/Cengage Learning) Figure 2.7 A generator supplying electric potential (voltage) to an electric circuit. (Delmar/Cengage Learning)

Current Flow Electron flow in an electric circuit –Obtained by a bolt of lighting, static electricity, or electron flow from a generator –Types: Direct current: flows in one direction Alternating current: reverses direction at regular intervals –Measured in amperes (A)

Resistance Opposition to flow of free electrons –Measured in ohms Figure 2.9 Two electric systems with different resistances. (Delmar/Cengage Learning)

Electric Power and Energy Electric power: –Rate at which the electrons do work Rate at which electricity is being used –Measured in watts (W) Electric energy: –Rate at which electric power is being used at a specific time Measured in watthours (Wh)

Ohm’s Law Relationship among current, electromotive force, and resistance Figure 2.13 Using Ohm’s law (not applicable on AC inductive circuits). (Delmar/Cengage Learning)

Calculating Electric Power Formula to calculate electric power: P = IE Two other formulas: P = E 2 /R P = I 2 R