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.
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?
6. Where do charges come from?
Matter is made up of atoms.
+
+
+
–
–
–
+
–
Proton (positive charge)
neutron (neutral)
electron (negative charge)
atom nucleus
8. Electrons…
• Are located on the outer
outer edges of
atoms…they can be moved
moved.
• A concentration
concentration of electrons in an
atom creates a net negative
negative charge.
• If electrons are stripped
stripped away, the
atom becomes positively
positively charged.
11. Coulomb’s law
• The magnitude of the force between 2
equal sized objects
• Fe = K q1 q2
r2
K (electrostatic constant =9 x 109
N m2
/C2
)
q (charge in Coulombs)
r ( distance between the charges)
r
Fe
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.
•Fe = K q1 q2
r2
= (8.99 x 109
N m2
/C2
) (6.0 x 10 -6
C) (3.0 x 10 -6
C)
( 0.030m )2
= (8.99 x 109
N m2
/C2
) (18.0 x 10 -12
C)
(9.0 x 10 -4
m2
)
= + 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 flow
does not flow.
.
• Static electricity is
potential energy
potential energy. It does
not
not move. It is stored
stored.
14. Static Discharge…
• Occurs when there is a loss
loss of static
electricity due to three possible
things:
• Friction
Friction - rubbing
• Conduction
Conduction – direct contact
• Induction
Induction – through an electrical
field (not direct contact)
15. Electricity that moves…
• Current
Current: The flow of electrons from
one place to another.
• Measured in Amperes
Amperes (Amps)
• Kinetic
Kinetic energy
16. Conductors vs. Insulators
• Conductors
Conductors – material through
which electric current flows easily
easily.
• Insulators
Insulators – materials through
which electric current cannot move
cannot move.
18. What is Resistance?
• The opposition
opposition to the flow of an
electric current, producing heat
heat.
• The greater
greater the resistance, the less
less
current gets through.
• Good
Good conductors have low
low
resistance.
19. What Influences Resistance?
• Material of wire
Material of wire – aluminum and
copper have low resistance
• Thickness
Thickness – the thicker the wire the
lower the resistance
• Length
Length – shorter wire has lower
resistance
• Temperature
Temperature – lower temperature
has lower resistance
20. The unit for measuring resistance is the
Ohm (
Ohm (Ω
Ω).
).
21. What is Voltage?
• The measure of energy
measure of energy given to the
charge flowing in a circuit.
• The greater
greater 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
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.
