• It is believed that Thales of Miletus, one
of the wise men of ancient
Greece, discovered the phenomenon
called static electricity. He observed at
around 600 B.C. that amber, a fossilized
resin attracted tiny particles of wood
when rubbed with wool.
• During the later part of the 15th century,
Sir William Gilbert, an English scientist, made
a number of experiments to investigate the
Properties of loadstones and amber. These started
the first systematic study of static electricity. In his
book “De Magnete”,published in 1600, he reported
his findings and conclusions. He introduced the
word “electric” to designate materials which
behave like amber.
5. • Electric Charge- is a basic property of certain
elementary particles of which all matter is
composed. There are two kinds of electric
charge, positive charge and negative charge.
• Electron - negatively charged particles of an
• Proton - positively charged particles of an
6. Modern plastics can now be used to obtain
positive and negative charges. Polythene strip
can acquire a negative charge when it is rubbed
with a duster. On the other hand, a
cellulose acetate strip can acquire positive
charge using the same duster.
Like charges repel and unlike
7. The Electron Theory
When two substances are rubbed
together, the electrons are the ones transferred
from one substance to the other. Substances
became positive when some electrons are
removed from them and become negative when
some electrons are added to them.
8. A device to detect the presence of electric
charges can facilitate the study of electrostatics.
The electroscope is a simple instrument which
can do this.
9. The electroscope consists of a light strip of
metal foil or paper hinged to the metal rods or
stem. This metal rod is connected to the metal
cap or disk and the whole assembly is mounted
in a plastic or glass container.
This separation of
charges when there is a
charged material nearby
is called electrostatic
10. Conductors and Insulators
Conductors allow current to move through it .
This indicates that electricity is not possible without
them. On the other hand, insulators are also valuable in
the sense that they stop charges from flowing from one
conductor to another.
Most materials are good conductors because
they contain large numbers free electrons per unit
volume. Insulators contain practically no free
electrons. The electrons in them are tightly bound
and normally charge does not flow.
11. Electrostatic Generator
• There are two main types of electrostatic generators
which are traditional items in a physics laboratory.
They are the electrophorus and the Van de Graaf
12. Electrostatic Generators
The electrophorus is a simple electrostatic generator
invented by Alessandro Volta.
It has a non-conducting base and a metal plate with
an insulated handle. The base acquires a negative
charge on being rubbed with fur. When the
metal plate is placed on the base, it is strongly
charged by induction. Then grounding will leave the
plate charged positively.
13. Electrostatic Generators
• The Van De Graaf generator is a machine used
to charge objects easily. It is capable of
producing very high voltage in the order of
10 MV with respect to the ground.
15. Coulomb’s Law
• Charles Coulomb – a French Physicist, made
the first quantitative investigation of electric
forces with the use of a torsion balance which
• Coulomb’s Law – states that the force exerted
by one charged object on another is
proportional to the product of the magnitude
of the charges and is inversely proportional to
the square of the distance between them.
16. Sample Problem
1. Find the electric force between two
electrons which are separated by a distance of
1mm. The charge of an electron is
1.6 x 10 ⁻¹⁹C.
17. • Electric Field – is a region around a charged
object where any charge placed in it
experiences a force which is electrical in
• Electric Field Intensity – is defined as the force
per unit charge acting on a charged object
placed at that point in the field.
The electric field intensity at a point varies inversely as the
square of the distance “r” of the point from Q and directly as
the magnitude of the charge.
18. Sample Problem
2. How much is the electric field intensity
at a point 1m away from a charge of
10 x 10⁻⁶C?
19. Electric Lines of Force
An Electric field can be described
visually by drawing lines of electric force.
These lines will represent the direction of
motion of a small “free” positive charge
placed in the field. The density of the lines
is used to indicate the intensity of the field.
If the charge is positive, the lines of electric
force are directed away from it. The lines of
electric force is directed towards the charge
if it is negative.
20. Electric Potential and Electric Potential
• Electric potential – work done in bringing
charge from a point of zero potential to that
• Electric Potential Difference – work done in
transferring a charge from one point to
• Electron volt – is the energy acquired by an
electron that has been accelerated through a
potential difference of 1 volt.
22. Electric Current
• Electric current – rate of flow of electric
• Ampere – unit of electric current in the MKS
system. This is equal to a flow of one coulomb
of charge per second.
• Andre Marie Ampere – a french
mathematician and physicist who formulated
some fundamental laws of electricity and
23. Sample Problem
3. How much current is produced if
3.75 x 10²⁰ electrons pass a given point in a
conductor in one minute? The charge of an
electron is 1.6 x 10⁻¹⁹C.
24. • Sources of EMF – is any device that will
transform non-electrical energy into electrical
• EMF – electromotive force
difference in potential between the
electrodes of a source in an open circuit.
• Cell – an electron pump
• Battery – a device for storing and generating
an electric current by chemical reaction. This
is a series of cells.
27. Series Circuit
• If we connect 2 or more lamps as shown in the
figure, all the electrons that go through 1
lamp must also go to the other lamps.
28. Parallel Circuit
• If we connect a cell to 2 or more lamps, as shown in
this figure, we say that the lamps are connected in
parallel. As the electrons reach point N, they divide
between the branches of the circuit until they reach
point M where they join together again.
29. Electric Circuit
An instrument which measures the current
in a circuit is called an ammeter. It is always
connected in series in the circuit. On the other
hand, an instrument which measures potential
difference is called a Voltmeter.
30. Ohm’s Law and Resistance
In 1826, George Simon Ohm, a German physicist,
discovered that the current (I) through a metal wire is
proportional to the potential difference (V) across it provided
that the temperature is kept constant.
This relationship is called Ohm’s Law.
31. This means that the Current (I) is
proportional to the voltage or potential
In equation form it is V/I = R, where the
constant R stands for the resistance of the
We define resistance of a wire as the ratio
of potential difference to the current. This
definition is actually the Ohm’s Law.
32. Sample Problem
4. A potential difference of 12V is applied
across an electric circuit.
a.) What is the current in the circuit if the
resistance is 30 Ohm’s?
b.) If the resistance in the circuit is
doubled, what is the current?
33. Factors Affecting Resistance
The resistance of a conducting wire that
obeys Ohm’s Law depends upon 3 factors:
1. The material of which it is made
2. The length of the wire
3. The cross-sectional area of the wire
It was found that the longer the wire the smaller the
current across it.
On the other hand, when the cross-sectional area of a
wire is increased, the resistance it offers to the flow of
electric charges becomes smaller.
34. Sample Problem
5. What length of resistance wire of
resistivity 100 x 10 ⁻⁸ ohm-m, and of cross-
section 2.5 x 10 ⁻⁷ m² would be needed to
make a resistor 57.6 ohms?
In 1911, an astonishing discovery was
made by M. Kamerlingh Onnes who won a
Nobel Prize for it. He found that when
mercury is cooled at 4.2°C above absolute
zero, its resistance suddenly disappears
entirely. The material exhibits the property of
36. • Superconductors- are materials that lose all
resistance when cooled to temperatures near
absolute zero. Current once started, flows in
This indicates that there is no need to replace
energy that is lost to resistance if
superconductors are used. So superconductors
may become the key to tremendous savings of
energy and money.
A resistor is a device used to
introduce resistance into an electrical
circuit. Resistors are sometimes made
of a length of nichrome wire. Resistors
can be used to reduce the current in a
39. Resistors in Series
When resistors are in series, the combined
resistance is the sum of the individual
resistances in the combination and is
therefore greater than any individual
40. Sample Problem
6. A potential difference of 6 V is applied to 2
resistors of 8 Ω and 4 Ω connected in series.
a.) The combined resistance of the 2
b.) The current flowing in the circuit
c.) The potential difference across the
8 Ω resistor.
41. Resistors in Parallel
When resistors are connected in
parallel, the reciprocal of the
combined resistance is equal to the
sum of the reciprocals of the
1/R= 1/R₁ + 1/R₂ + 1/R₃
42. Sample Problem
7. A potential difference of 12V is applied to
2 resistors (3Ω and 6Ω) connected in
a.) The combined resistance of the 2
b.) The current flowing in the main circuit
c.) The current in the 6Ω resistor
43. • Power – is defined as the rate of doing work, or
the rate at which energy is produced. In simple
terms, power is the amount of work done in a
unit of time.
Power = Work/ time
P= V I
P= I² R
P= V²/ R
Power is measured in joules per second which
is called watt.
44. Sample Problem
8. A burning lamp is marked 22W, 220V
a.) How much current flows through the
b.) What is its resistance?
The term Magnetism comes from the
region of Magnesia, an island in the Aegean
Sea where certain stones were found by the
Greeks more than 2000 years ago. The
stones called “ lodestones” had the unusual
property of attracting pieces of iron.
Magnets were first fashioned into
compasses and used for navigation by the
Chinese in the 12th century.
If the north pole of one magnet is
brought near the north pole of another
magnet, they repel. The same is true of a
south pole near another south pole. If
opposite poles are brought near each
other, attraction occurs. Hence, these
observations can be stated as follows:
unlike poles attract and like poles repel.
Magnetic poles behave similarly to electric
charges in this aspect of attraction and
repulsion. But they are very much different in
that while an electron and a proton can exist
separately, a north pole and a south pole
cannot. They always come in pairs.
52. Coulomb’s Law of Magnetism
Coulomb’s law of magnetism states
that the force between 2 magnetic poles
is directly proportional to the product of
their pole strengths and inversely
proportional to the square of the distance
54. If a pole of a magnet is brought to touch
one end of the first clip, the second clip can be
picked up by the first. This means that the clip
which is in contact with the magnet, becomes
a magnet itself. We call this phenomenon as
55. Magnetic Fields
A magnetic field is a region or space in
which a magnet pole placed in it experiences a
force which is magnetic in nature. An electric
field and a magnetic field have similar
characteristics but they are not equivalent.
56. Magnetic Field
The path taken by an imaginary “free”
N- Pole in a magnetic field is called a magnetic
line of force or a line of flux.
57. These flux lines in a magnetic field are
collectively called magnetic flux
represented by the Greek letter phi Ø.
The unit of magnetic flux in MKS System
is the Weber. One weber is equal to 10⁸
lines of flux.
60. Theory of Magnetism
Since electron is a charged particle, this
theory implies that magnetism is a property of a
charge in motion. Two types of electron motion
are regarded as important in this concept of
First, the revolution of the electron about the
nucleus of an atom imparts magnetic property to
the structure of the atom.
The second type of motion is the spinning of
the electron on its own axis.
61. How Magnets are Made
• Stroking Method
• Electrical Method
• By hammering
• By heating
63. Magnetic effect of an Electric Current
In 1813, a Danish Physicist Hans Christian
Oersted predicted that a relationship
between electricity and magnetism would be
found. In 1819, seven years later, Oersted
himself discovered that electricity has a
magnetic effect. He found that a small
compass needle is deflected when brought
near a conductor carrying an electric current.
This was the first evidence of the suspected
relationship between electricity and
65. Forces Between Current-carrying
After Oersted’s discovery of the magnetic
effect of an electric current, a French physicist
Andre Marie Ampere determined the shape of
the magnetic field about a conductor carrying
a current. Earlier he had discovered that forces
exist between two parallel conductors in a
circuit. If the current in the parallel conductors
are in the same direction, the two conductors
attract one another. The force between the
two conductors are repulsive if the currents
are in opposite directions.
67. As to the determination of the direction of
the magnetic field around the conductor, we
can make use of the right-hand rule for
68. The magnitude of the magnetic field B also
called as magnetic flux density or magnetic
induction, at any point in the magnetic field of
a current- carrying conductor is directly
proportional to the current in the conductor
and inversely proportional to the radial
distance, r , of the point from the conductor.
69. Sample Problem
10. A long straight wire carries a current of
12 A. how much is the magnetic flux density at
a point 0.1 meter from the conductor?
70. Uses of Electromagnets
• In electric Bell and electric Buzzer
• In Electromagnetic Relays
• In Telephone Earpiece and in Radio Earphone
71. Force on a Current-carrying Conductor
in a Magnetic field
The force on the wire depends upon
the strengths of the 2 magnetic fields.
Thus, a force may be increased by
increasing the current in the wire and by
increasing the strength of the uniform
72. Fleming’s Left-hand Rule
states that if the thumb, forefinger and the middle
finger of the left hand are held at right angles to each
other, then the forefinger points in the direction of the
magnetic field, the center finger points in the direction
of the conventional current and the thumb points in the
direction of the force on the wire.
73. Electromagnetic Induction
In 1831, Michael Faraday discovered how to
make electricity using magnetism. He found out that
an electromotive force is set up in a conductor
located in a magnetic field, when the magnetic flux is
cut by the conductor. Joseph Henry, at about the
same time made a similar discovery.
Electromagnetic Induction- current is induced in the
wire, if the wire is moved to cut across lines of force
74. Fleming’s Right-hand Rule
states that if your right-hand is held in a
fist and thumb, the forefinger and the middle
finger are spread out at right angles to each
other, the forefinger points in the direction of
the magnetic field, the thumb points in the
direction of the movement of the wire and the
middle finger points in the direction of the