This document provides an overview of 4 lessons on electricity and magnetism: Lesson 1 introduces electric charge and static electricity, including how objects become charged through friction or conduction. Lesson 2 explains Coulomb's Law, which describes the electric force between two point charges. Lesson 3 defines electric fields as physical fields that exert forces on charged particles. It discusses electric field lines and how they indicate the direction and strength of electric fields. Lesson 4 introduces electric potential and electric potential energy, including how more energy is required to move a charge through a stronger electric field or further in an electric field.

2. GENERAL
PHYSICS 2

3. Unit Topic: Electricity and Magnetism: The Art of
Conserving Electricity
Lesson 1: Electric Charge and Static Electricity
Lesson 2: Coulomb’s Law
Lesson 3: Electric Field
Lesson 4: Electric Potential

4. Lesson 1:
Electric Charge and Static
Electricity

5. 5
Atoms & Electricity
• All matter is made of atoms, which contain electrons,
protons, and neutrons.
• Objects normally contain equal numbers of electrons and
protons: such objects are called neutral.
• When an object has an imbalance in the number of
electrons and protons, it is electrically charged.
• Neutrons are not involved in electric interactions.

6. 6
Electric Charge
• An object with more electrons than protons is said to carry a
negative charge.
• An object with more protons than electrons is said to carry a
positive charge.
• The imbalance between p+ and e– in a charged object is
proportionally very small…
• The difference may be only 1012 particles out of a total of
• 1025; i.e. an imbalance of 1 per 10 trillion!

7. 7
Electric Charge
• Like energy and momentum, electric charge is a conserved
quantity:
Charge cannot be created or destroyed, but it can be
transferred between objects.
• Charged objects exert electric forces on each other:
Opposite charges attract; Like charges
repel.

8. Ways to Transfer Electric
Charges

9. Charging by Friction
Rubber
Plastic
Cotton
Fur
Wool
Glass
Acetate
Negative
Positive
The electrostatic series shows
which material will be + and
which will be – when different
materials are rubbed together.
9

11. Charging by Conduction
• Charging by Conduction occurs when a
neutral object is placed in contact with an
already-charged object.
• If the object is –, electric repulsion will push
some of the excess electrons from the charged
to the neutral object.
1
1

12. Charging by Conduction
• If the objects are spheres of the same size, and
are made out of conductive material, they will
have the equal amounts of charge after
contact.
• The charge is located on the surface (not the
interior) because the electrons repel each
other.
1
2

13. Charging by Conduction
• In solids, protons are usually not mobile; only
electrons are able to move.
• If the object is +, electric attraction will pull
some electrons from the neutral object to the
charged one.
1
3

14. Charging by Induction
• Charging by Induction uses a similar
mechanism to polarization.
• A charged object (“A”) is brought close to
(but not touching) the object (“B”) to be
charged. This object is in connected to a
more distant object (“C”) such as Earth.
1
4

15. Charging by Induction
• “A” produces electric force, causing electrons
to flow between “B” and “C”.
• When “B” and “C” are separated, “B” has a
charge of the opposite sign compared to “A”.
• “C” has a charge of the same sign as “A”.
1
5

17. STATIC ELECRICITY
Static electricity is an imbalance of electric charges
within or on the surface of a material.

18. Lesson 2:
Coulomb’s Law

19. Coulomb’s Law – Gives the electric force between
two point charges.
2
2
1
r
q
q
k
F 
k = Coulomb’s Constant =
9.0x109 Nm2/C2
q1 = charge on mass 1
q2 = charge on mass 2
r = the distance between the
two charges

22. Example 2
Two 40 gram masses each with a charge of 3μC are placed
50cm apart. What is the electrical force acting on the charges?
3μC
40g
50cm
3μC
40g
Charge
(microcoulomb)
Charge
(coulomb)
1 μC 0.000001 C

23. 2
2
1
r
q
q
k
FE 
2
6
6
9
)
5
.
0
(
)
10
3
)(
10
3
(
10
0
.
9






N
324
.
0


25. Find the force between charges of +10.0 µC and -50.0 µC located
20.0 cm apart.

26. 1. Two equal charges of magnitude 1.1 x 107 C experience an
electrostatic force of 4.2 x 104 N. How far apart are the centers of
the two charges?
2. What is the magnitude of the force a 1.5 x 106 C charge exerts
on a 3.2 x 104 C charge located 1.5 m away?
3. A negative charge of - 2.0 C and a positive charge of 3.0 C are
separated by 80 m. What is the force between the two charges?
4. A negative charge of - 0.0005 C exerts an attractive force of 9.0
N on a second charge that is 10 m away. What is the magnitude
of the second charge?

27. Lesson 3:
Electric Field

28. • An electric field is the physical field that surrounds electrically
charged particles and exerts force on all other charged particles in the
field, either attracting or repelling them.
• The electric field can be visualized with a set of lines whose direction
at each point is the same as the field's, a concept introduced
by Michael Faraday, whose term 'lines of force' is still sometimes
used.

29. Electric Field Strength
• The magnitude of the electric field
is simply defined as the force per
charge on the test charge.
Units of
N/C

30. Equations -
Summary
• Coulomb’s Law
– units: N
• Electric Field Strength
– units: N/C
• Electric Field Strength
(a second equation)

32. Electric FieldLines
• Electric field lines can be used to draw an electric field.

33. Electric Field Lines are VECTORS

34. Electric Field Lines

35. • Electric field lines never cross one
another.
• Field lines show both the direction of an
electric field and the relative strength
due to a given charge.
• More lines are drawn for greater
charges to indicate greater force.

36. Direction of Electric Fields
• By convention, the test charge is assumed positive when assigning direction
arrows to field lines.
• Since like charges repel and opposites attract, electric field vectors will always
point
– away from positive source charges
– toward negative source charges
• Electric Field lines do not cross
• The electric field is stronger when the lines are located closer to one another.

37. Some Common Mistakes
1. Lines not spread out evenly around charges

38. 2. Too few lines to sufficiently describe the
space surrounding the charges

39. 3. Lines too short to sufficiently describe the
space surrounding the charges
(The space in between the charges is not described by this drawing).

40. (better)

41. 4. Lines intersecting (or about to intersect if
lengthened).

42. Lesson 4:
Electric Potentials

43. Chapter II: Electric Potential and Electric
Potential Energy
• Electrical energy is very important in our daily life. It is a
basic necessity.
• We are aware that electricity is produced in electrical
generating plants. These plants send out electrical power
along high-voltage transmission lines and deliver it to
electrical substations. In these substations, the high- voltage
power transmitted is converted into lower voltage that can
be distributed to the users.

44. Two of the most familiar aspects of electricity are its
energy and voltage.

45. Electric potential energy is
the energy that is needed to move
a charge against an electric field.
You need more energy to move a
charge further in the electric field,
but also more energy to move it
through a stronger electric field

47. 1. An incandescent light bulb that is turned off.
2. Your car's headlights before they are turned on.
3. A radio tower that is not working.

48. A point charge of +0.80 μC is located at the origin, and a second point
charge of −4 μC is at x = 40 cm. What is the electric potential energy
stored in the two charge system?

51. Unit for
Potential