The nature of electricity

1. The Nature of Electricity
Kendeo

2. Objectives
1.Explain the nature of electricity.
2.Describe the materials that interact with electric
charges.
3.State Coulomb’s Law and its relationship in
electric fields.
4.Explain Ohm’s Law.
5.Solve problems involving Coulomb’s Law and
Ohm’s Law.

3. Electrostatics
0
The interaction between static electric charges is called
electrostatics.

4. The van de Graaf generator (large silver ball)
deposits electrons on the ball. When a person
places their hand on the ball and the machine is
turned on, electrons are transferred to and
collected on the person touching the silver ball.
Why do you
think this
machine
affects the
hair of the
children in the
picture?

5. What is electricity?
The collection or flow of
electrons in the form of
an electric charge

6. Where do charges come from?
Matter is made up of atoms.
+
+
+
–
––
+
–
Proton (positive charge)
neutron (neutral)
electron (negative charge)
atom nucleus

7. +
-
+
+
+
+
The world is filled with electrical charges:
+
+
+
+
+
-
-
- -
-
-
- --

8. Electrons…
•Are located on the outerouter edges of
atoms…they can be movedmoved.
•A concentrationconcentration of electrons in an
atom creates a net negativenegative charge.
•If electrons are strippedstripped away, the
atom becomes positivelypositively charged.

9. Charges interact with each other:

11. Coulomb’s law
•The magnitude of the force between 2
equal sized objects
•F
e
= K q
1
q
2

r
2
K (electrostatic constant =9 x 10
9
N m
2
/C
2
)
q (charge in Coulombs)
r ( distance between the charges)
r
F
e

12. Coulombs Law Examples
•A positive charge of 6.0 x 10
-6
C is 0.030m from a second positive
charge of 3.0 x 10
-6
C. Calculate the force between the charges.
•F
e
= K q
1
q
2

r
2
= (8.99 x 10
9
N m
2
/C
2
) (6.0 x 10
-6
C) (3.0 x 10
-6
C)
( 0.030m )
2
=

(8.99 x 10
9
N m
2
/C
2
) (18.0 x 10
-12
C)
(9.0 x 10
-4
m
2
)
= + 1.8 x 10
-8
N

13. What Is Static Electricity?
•A stationary electrical
charge that is built up on
the surface of a material
•The charge builds up but
does not flowdoes not flow..
•Static electricity is
potential energypotential energy. It does
notnot move. It is storedstored.

14. Static Discharge…
•Occurs when there is a lossloss of static
electricity due to three possible
things:
•FrictionFriction - rubbing
•ConductionConduction – direct contact
•InductionInduction – through an electrical
field (not direct contact)

15. Electricity that moves…
•CurrentCurrent: The flow of electrons from
one place to another.
•Measured in AmperesAmperes (Amps)
•KineticKinetic energy

16. Conductors vs. Insulators
•ConductorsConductors – material through
which electric current flows easilyeasily.
•InsulatorsInsulators – materials through
which electric current cannot movecannot move.

17. Examples
•ConductorsConductors:
–Metal
–Water
•InsulatorsInsulators:
–Styrofoam
–Rubber
–Plastic
–Paper

18. What is Resistance?
•The oppositionopposition to the flow of an
electric current, producing heatheat.
•The greatergreater the resistance, the lessless
current gets through.
•GoodGood conductors have lowlow
resistance.

19. What Influences Resistance?
•Material of wireMaterial of wire – aluminum and
copper have low resistance
•ThicknessThickness – the thicker the wire the
lower the resistance
•LengthLength – shorter wire has lower
resistance
•TemperatureTemperature – lower temperature
has lower resistance

20. The unit for measuring resistance is the
Ohm (Ohm (ΩΩ).).

21. What is Voltage?
•The measure of energymeasure of energy given to the
charge flowing in a circuit.
•The greatergreater the voltage, the greater greater
the force or “pressure”the force or “pressure” that drives
the charge through the circuit.

22. Other Types of Conductors
•Electrolytes
–Both negative and positive charges can move
•Semiconductors
–In-between conductors and insulators in their
ability to conduct electricity

23. Ohm’s Law
Current is directly proportional to voltage and inversely proportional to
resistance.
V
IR

24. Practice with Ohm’s Law
OhmsOhms VoltsVolts AmpsAmps
44 100100 2525
1515 150150 1010
22 3030 1515
99 4545 55
66 4848 88

25. What causes you to be shocked when you rub your feet
across carpet?
An electrical discharge is the passing of an electric
current through the air from a negatively charged object
to a positively charge object. This is what causes
lightning!

26. Grounding
An object is grounded when it is connected to
the earth through a connecting wire.
If a charged conductor is grounded, it
will become neutral.

27. Ohm’s Law Example 1
I =
3 V
2 Ω
I = 1.5 Amps

28. Example 2:
A light bulb operates on a 110 volt circuit. The bulb draws a current of .
91 amps. What is the resistance of the light bulb?
V=IR
R=V/I
R=110V/.91A
120.8 Ohms, Ω

29. How Electricity Impacts Today's
Life
•We use electricity for
light, heat,
transportation,
everything!
•Can you cite other
uses of electricity?