Essentials of Electronics

Second Edition

Frank D. Petruzella

Glencoe/McGraw-Hill

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.

CHAPTER 4

SOURCES AND CHARACTERISTICS

OF ELECTRICITY

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

Fur and rubber rod rubbed together

Charge accumulatesat end of rod only

Electrons move from the fur to the rod

Negative chargeproduced on the rod

Law of Electric Charges

Like charges repel

Unlike charges attract

Charging by Contact

Neutral

Positive chargeproduced

Negative chargeproduced

Electroscope

Charging by Induction

Metalsphere

Insulatedstand

Placing negative charge near sphere causes

redistribution of charges

Grounding sphere allowselectrons to leave

When ground is removedsphere remains positively charged

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.

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

Battery Symbol

Waveform

Alternating Current (ac) Electricity

Outlet

Symbol

Waveform

Producing Electricity from Light

SolarCell

PracticalApplication

Video on how a solar cell workshttp://www.youtube.com/watch?v=x2zjdtxrisc

Producing Electricity by Means of aChemical Reaction

Electrons move from the positive electrode tothe negative electrode of the battery.

Positive Electrode Negative Electrode

ElectrolyteSolution

http://www.rayovac.com/wizard/battery_howwork.htm

Producing Electricity Using Heat

IndustrialThermocouple

Thermocoupleheated at junction

Millivoltmeter:calibrated in degrees

Iron:losses electrons

Copper:gains electrons

http://en.wikipedia.org/wiki/Thermocouple

Pressure exertedon crystal

Producing Electricity Using Pressure

Voltage produced at plates

Practical use:microphone

http://www.explainthatstuff.com/piezoelectricity.html

Coiledconductor

Producing Electricity Using Mechanical-Magnetic Action

Voltage generated

Application:generator

Movingmagnetic

field