Essentials of Electronics Second Edition Frank D. Petruzella Glencoe/McGraw-Hill

CHAPTER 4 SOURCES AND CHARACTERISTICS OF ELECTRICITY Most materials belong to one of three Any device that develops and maintains a voltage can be considered a voltage source. To create electricity, the voltage source causes electrons to move from one point to another point.

CHAPTER 4 SOURCES AND CHARACTERISTICS OF ELECTRICITY In this chapter, we will explore the different methods used to produce voltage.

OBJECTIVES Define static and current electricity. Explain how static positive and negative charges are produced. State the law of electric charges. Explain the difference between direct current (dc) and alternating current (ac) electricity. List the basic sources of electricity and electrical devices used to convert the various energy forms.

What is Electricity? The flow of free electrons through a conductor. What else is electricity??? http://www.amasci.com/miscon/whatis.html

Producing Static Electricity by Friction Charge accumulates at end of rod only Fur and rubber rod rubbed together Negative charge produced on the rod Electrons move from the fur to the rod

Law of Electric Charges Like charges repel Unlike charges attract Animate the movement of the charged balls as indicated

Charging by Contact Electroscope Negative charge Positive charge produced Positive charge produced Animate the movement of the charged balls as indicated Neutral

Charging by Induction Metal sphere Insulated stand Animate the movement of the charged balls as indicated

Placing negative charge redistribution of charges near sphere causes redistribution of charges Animate the movement of the charged balls as indicated

Grounding sphere allows electrons to leave Animate the movement of the charged balls as indicated

sphere remains positively charged When ground is removed sphere remains positively charged Animate the movement of the charged balls as indicated

Materials which are called electrical "INSULATORS" have electrons strongly attached to the nucleus of the atoms in the material so that no flow of electrons (or current) can take place in the material. Materials which are called electrical "CONDUCTORS" have electrons which can leave the atoms and migrate freely through the material. Most metals are good electrical conductors because they only have a few electrons in the outer shell of the atom which can be easily detached and moved through the material,becoming an electric current. When a negatively charged rod is placed close to the neutral metal sphere the (negatively) charged electrons in the sphere are repelled to the far side of the sphere, leaving the atoms on the near side positively charged owing to their missing electrons. If we then connect a copper wire to the negative side of the sphere and an electrical ground some of the free electrons will flow into the ground. When we then remove the copper wire and the negatively charged rod what remains is a metal sphere with a uniform distributed positively charge.

Electrical Charge in Motion Current Electricity Electrical Charge in Motion

Electromotive Force Emf, Voltage, V, E all the same… Pressure that causes electrons to flow. From the primary sources of energy…

Direct Current (dc) Electricity Symbol Battery Waveform Animate the movement of the electrons

Alternating Current (ac) Electricity Symbol Waveform Outlet Animate the movement of the electrons

Producing Electricity from Light Video on how a solar cell works http://www.youtube.com/watch?v=x2zjdtxrisc Practical Application Solar Cell

Producing Electricity by Means of a Chemical Reaction Electrolyte Solution Animate movement of electrons Positive Electrode Negative Electrode Electrons move from the positive electrode to the negative electrode of the battery. http://www.rayovac.com/wizard/battery_howwork.htm

Producing Electricity Using Heat Millivoltmeter: calibrated in degrees Industrial Thermocouple Iron: losses electrons Copper: gains electrons Animate movement of electrons http://en.wikipedia.org/wiki/Thermocouple Thermocouple heated at junction

Producing Electricity Using Pressure Voltage produced at plates http://www.explainthatstuff.com/piezoelectricity.html Practical use: microphone Animate movement of electrons Pressure exerted on crystal

Producing Electricity Using Mechanical-Magnetic Action Coiled conductor Application: generator Moving magnetic field Animate movement of electrons Voltage generated