Electronics
Nature of Electricity
Copyright © Texas Education Agency, 2013. All rights reserved.
1
Specific Objectives






State the law of charges
Explain the law of charges using several examples
Explain what electric current, voltage, and
resistance mean
Describe electrical work
Describe differences between conductors, insulators,
and semiconductors
Describe where conductors, insulators, and
semiconductors are used
Copyright © Texas Education Agency, 2013. All rights reserved.
2
UNT in partnership with TEA. Copyright ©. All rights reserved.
Law of Charges
This is also called Coulombs Law.
Charge is a fundamental property of electrons
and protons.
Charged particles have an invisible force field
around them, which interact according to their
respective charge.





Positive or negative
Like charges repel each other while unlike charges
attract each other.
Copyright © Texas Education Agency, 2013. All rights reserved.
4
Law of Electrical Charges
A.
Like charges repel
Example: Electrons repel electrons
B.
Unlike charges attract
Example: Protons attract electrons
Copyright © Texas Education Agency, 2013. All rights reserved.
5
Demonstration of Coulombs Law
Requirements




One piece of fur
One vulcanite rod
Two pith balls hanging from a beam
Directions

1.
2.
3.
Negatively charge the vulcanite rod with the
piece of fur.
Bring the rod close to one hanging pith ball.
Observe that the ball is first attracted to the rod
because of unlike charges. When the ball
touches the rod, it is immediately repelled.
Copyright © Texas Education Agency, 2013. All rights reserved.
6
Coulomb’s Law (continued)
4.
5.
6.
7.
Continue to attempt to touch the pith ball with the
vulcanite rod.
Recharge the vulcanite rod and touch it to the
second pith ball. You now have two negatively
charged pith balls.
Bring the two pith balls near each other. Do your
observations match?
Charge up the glass rod by rubbing it with a piece of
silk. Touch the glass rod to one of the pith balls.
Leave the other negatively charged.
Copyright © Texas Education Agency, 2013. All rights reserved.
7
Coulomb’s Law (continued)

Question

Why has the pith ball
acted this way?

Answer

Like poles repel each
other; unlike poles
attract each other.
Copyright © Texas Education Agency, 2013. All rights reserved.
8
What is Electricity?

Electricity is a general term that describes the type of
energy source.




Other energy sources include chemical, heat, mechanical,
or light energy.
Each of these energy sources can be converted into
electrical energy.
Electrical energy can be converted back into any of these
types of energy to do work.
Electricity is a convenient way to deliver energy for
general use.
Copyright © Texas Education Agency, 2013. All rights reserved.
9
Important Electrical Terms

Current is the movement of electrons in a conductor.


Voltage is the force behind the electrons. It moves
them along the conductor resulting in current.


(Measured in amps)
(Measured in volts)
Resistance is the quality of an electric circuit that
opposes the flow of the current through it.

(A measurement of the opposition to current flow
in ohms [Ω])
Copyright © Texas Education Agency, 2013. All rights reserved.
10
What is Voltage?



A difference in potential
 Always relative – compares something to
something else
 Measurement made between two things or places
An invisible force that acts on charged particles
Created by a separation and collection of
opposite charges
 Electrons separated from a nucleus
Copyright © Texas Education Agency, 2013. All rights reserved.
11
What is Current?



The movement of electrons directed by an external
force
The force can be an electrical force
 Voltage
 The force between charged particles
 Described by Coulombs Law
The force can be created by magnetism
 A conductor moving through a magnetic field
 Generator action
Copyright © Texas Education Agency, 2013. All rights reserved.
12
Random Drift of Electrons
The movement of an electron occurring naturally
with no controlling force applied.
 This movement is random. This means that there is
no collective or net movement of electrons.
 Heat is a primary energy source.
 Creates free electrons in a conductor, but does not
direct their movement.
 Even when no controlling or directing force is
present, electrons can move from the orbit of one
atom to the orbit of another.
Copyright © Texas Education Agency, 2013. All rights reserved.
13
AC and DC Current


AC = Alternating
Current
A current of electrons
that moves first in one
direction and then in
the other.



DC = Direct Current
A flow of electrons in
one direction.

Created by a battery
Created by a generator
 Both forms are used to create work.
 AC is more efficient to send over long distances
because the voltage can be stepped up with
a transformer.
Copyright © Texas Education Agency, 2013. All rights reserved.
14
Electrical Work





Work is defined as force times distance.
Something has to move for work to be done.
Electrons are the “something” that moves to create
electrical work.
Current is the measurement for the amount of
movement by electrons.
More current equals more work.
Copyright © Texas Education Agency, 2013. All rights reserved.
15
Conductor, Insulator,
Semiconductor

A conductor of electricity is anything that
permits the free flow of electrons.
 A good conductor has many free electrons.

An insulator is a material that will not permit the free
flow of electrons.
 An insulator has no free electrons.
 An insulator is a poor conductor of electricity.

A semiconductor is a material that limits the flow of
free electrons.
 A semiconductor has few free electrons.
Copyright © Texas Education Agency, 2013. All rights reserved.
16
Conductor, Insulator,
Semiconductor (continued)



Conductors are used to deliver voltage where it
is needed (like an electrical outlet).
Insulators are used to keep voltage from going
where it is not wanted (for safety and protection).
Semiconductors are used to control the amount
and direction of current flow.
Copyright © Texas Education Agency, 2013. All rights reserved.
17
Conductors, Insulators, and
Semiconductors (continued)
Conductors
Insulators
Semiconductors
Copper
Bakelite
Selenium
Iron
Glass
Silicon
Steel
Mica
Germanium
Aluminum
Porcelain
Cuprous Oxide
Silver
Air
Lead Sulfide
Tin
Dry Wood
Silicon Carbide
Damp Earth
Sand
Gallium Arsenide
Salt Water
Rubber
Gallium Phosphide
Copyright © Texas Education Agency, 2013. All rights reserved.
18