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

2. 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.

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

4. 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.

5. What is Electricity? The flow of free electrons through a conductor.
What else is electricity???

6. 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

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

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

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

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

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

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

13. 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.

14. Electrical Charge in Motion
Current Electricity
Electrical Charge in Motion

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

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

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

18. Producing Electricity from Light Video on how a solar cell works
Practical
Application
Solar
Cell

19. 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.

20. Producing Electricity Using Heat
Millivoltmeter:
calibrated in degrees
Industrial
Thermocouple
Iron:
losses electrons
Copper:
gains electrons
Animate movement of electrons
Thermocouple
heated at junction

21. Producing Electricity Using Pressure
Voltage produced at plates
Practical use:
microphone
Animate movement of electrons
Pressure exerted
on crystal

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