Chapter 2 Basic Electricity Objectives Upon completion of

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’s law Power factor Proton

Key Terms (cont’d. ) • • • Resistance Seasonal energy efficiency ratio (SEER) Static electricity 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