Electricity is a form of energy that is invisible but can be observed through its effects, such as during lightning storms. It is caused by an imbalance of electric charges within atoms. Important early discoveries about electricity were made by scientists like Benjamin Franklin and Michael Faraday. Coulomb's law describes the force of attraction or repulsion between two charged objects. Static electricity occurs when friction separates electric charges within materials, causing them to become positively or negatively charged. Current electricity involves the flow of charged particles called electrons. Ohm's law defines the relationship between voltage, current, and resistance in an electrical circuit.

2. What is Electricity?
• It is a form of energy,
evident from the fact
that it runs machinery
and can be transformed
into other types of
energy such as light and
heat.
• It is invisible. During an
electrical storm, we do
not see electricity. We
observe the air being
ionized when the

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

4. Who Discovered Electricity?
The Greeks had some idea of electricity.
In the 18th century Franklin and other
Europeans knew a great deal about it. Early
in the century, Alessandro Volta invented
the first source of continuous electric
current - the battery. Later, Hans
Christian Oersted discovered that an
electric current produced magnetism.
But it was Michael Faraday who
described the nature of the phenomena. In
his electromagnetic induction theory he
stated that an electric current flows in a
conductor if that conductor is in a moving
magnetic field and is part of a circuit.

5. +
-
+
+
+
+
The world is filled with electrical charges:
+
+
+
+
+
-
-
-
- -
-
- - -

6. Electrons…
Are located on the outer edges of
atoms… They can be moved.
A concentration of electrons in an
atom creates a net negative charge.
If electrons are stripped away, the
atom becomes positively charged.

7. Charges interact with each other:

9. Coulomb’s law
• The magnitude of the force between
2 equal sized objects
• Fe = K q1 q2
K (electrostatic constant =9 x 109 N m2/C2)
q (charge in Coulombs)
r ( distance between the charges)
r2
F
e
r

10. Coulomb’s Law Examples
• A positive charge of 6.0 x 10 -6C is 0.030m from a second
positive charge of 3.0 x 10 -6C. Calculate the force between the
charges.
F
e
= K q
1
q
2
r2
= (8.99 x 109 N m2/C2 ) (6.0 x 10 -6C) (3.0 x 10 -6C)
( 0.030m )2
= (8.99 x 109 N m2/C2 ) (18.0 x 10 -12C)
(9.0 x 10 -4 m2)
= + 1.8 x 10 -8 N

11. van de
Graaff
generator
The interaction between static electric charges

12. What is Static Electricity?
Static electricity is electricity at rest. It is
produced by friction, by rubbing. All matter contains
positively charged particles called protons and
negatively charged particles called electrons. In an
uncharged atom, the protons and electrons balance
each other and the atom is neutral. If this neutral
atom loses an electron, because it has an excess of
protons, it is said to be positively charged. If the
neutral atom gains an electron, it is said to be
negatively charged.
Rubbing can tear electrons loose from certain
atoms. Some substances, because of the character of
their atoms, tend to lose electrons and become
positively charged; other substances gain electrons
easily and become negatively charged.

13. Static Discharge
• Occurs when there is a loss of
static electricity due to three
possible things:
• Friction - rubbing
• Conduction – direct contact
• Induction – through an
electrical field (not direct
contact)

14. Electricity that moves…
• Current - The flow of electrons
from one place to another.
• Measured in Amperes (Amps)
• Kinetic energy

15. Conductors vs. Insulators
Conductors – material
through which electric
current flows easily.
Insulators – materials
through which electric
current cannot move.

16. Examples
Conductors
Copper
Mercury
Silver
Aluminum
Human Body
Metallic Salts
Charcoal
Insulators
Wood
Rubber
Glass
Porcelain

18. • The opposition to the flow of
an electric current, producing
heat.
• The greater the resistance,
the less current gets through.
• Good conductors have low
resistance.

19. What Influences Resistance?
1. Material of wire –
aluminum and copper have
low resistance
2. Thickness – the thicker the
wire the lower the
resistance
3. Length – shorter wire has
lower resistance
4. Temperature – lower
temperature has lower

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

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

22. Current is directly proportional to
voltage and inversely proportional
to resistance.

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

24. 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