2. Electricity
phenomenon associated with
stationary or moving electric
charges. Electric charge is a
fundamental property of matter and
is borne by elementary particles. In
electricity the particle involved is the
electron , which carries a charge
designated, by convention, as
negative. Thus, the various
manifestations of electricity are the
result of the accumulation or motion
of numbers of electrons.
3. Thales
In about 600 BC, the Ancient
Greeks discovered that rubbing
fur on amber (fossilized tree
resin) caused an attraction
between the two – and so what
the Greeks discovered was
actually static electricity.
4. William Gilbert & Thomas Browne
In the year 1600, English physician
William Gilbert used the Latin word
“electricus” to describe the force that
certain substances exert when
rubbed against each other. A few
years later another English scientist,
Thomas Browne, wrote several
books and he used the word
“electricity” to describe his
investigations based on Gilbert’s
work.
5. Benjamin Franklin
In 1752, Ben Franklin conducted
his experiment with a kite, a key,
and a storm. This simply proved
that lightning and tiny electric
sparks were the same thing.
6. Alessandro Volta
Italian physicist Alessandro
Volta discovered that particular
chemical reactions could
produce electricity, and in 1800
he constructed the voltaic pile
(an early electric battery) that
produced a steady electric
current, and so he was the first
person to create a steady flow of
electrical charge.
7. Alessandro Volta
Volta also created the first
transmission of electricity by
linking positively-charged and
negatively-charged connectors
and driving an electrical charge,
or voltage, through them
8. Michael Faraday
Michael Faraday created the electric
dynamo (a crude power generator),
which solved the problem of
generating electric current in an
ongoing and practical way.
Faraday’s rather crude invention
used a magnet that was moved
inside a coil of copper wire, creating
a tiny electric current that flowed
through the wire.
9. Thomas Edison & Joseph Swan
Thomas Edison and Joseph Swan
who each invented the incandescent
filament light bulb in their respective
countries in about 1878. Previously,
light bulbs had been invented by
others, but the incandescent bulb
was the first practical bulb that would
light for hours on end.
10. What are the sources of electricity?
• Main electricity
• Electric cells
• So what’s the difference?
11. Main Electricity
• Generated by power stations
• Delivered to homes and
industries through wires
• Finally connected to main sockets
• Supplies a lot of electrical energy
• Electric shock
12. Electric Cells
• Used in many portable electrical
devices
• Supplies small amount of energy
• Safe to touch
13. Electric Current and
Circuit?
The rate of flow of electric charges
is called electric current
Electric circuit is the path which the
electric current takes
14. Parts of a Circuit
• Called electrical components
• Examples
– Connecting wires
– Bulb
– Switch
– Electric cell
15. Connecting wires
• Made of two types of materials
• Electrical conductor and electrical
insulator
Electrical
conductor –
made of
metal such as
copper
Electrical
insulator –
made of
plastic
16. Connecting wires
• Symbols of connecting wires
• Connecting wires (joined) and
connecting wires (not joined)
• See pg 56
Joined Not joined
21. Complete and incomplete
circuits
Complete circuits is also
known as closed circuits
Incomplete circuits is also
known as opened circuits
What is the difference between
the two?
22. Complete and incomplete
circuits
Complete circuits is also
known as closed circuits
Incomplete circuits is also
known as opened circuits
What is the difference between
the two?
23. Complete/Closed circuits
It is complete path without any
gaps from one end of the cell
to the light bulb and back to the
other end of the cell
24. Incomplete/Open circuits
The path is incomplete
Each circuit has a gap in it and
the bulbs do not light up
Example: no source of
electrical energy or connecting
wire is missing
See pg 55.
25. Types of Switches
• A switch is used to open or close a
circuit.
• Tap key switch
• A plug switch
• A mains switch used in buildings
• When switch is off, the circuit is
opened and the bulb will not light up
• When switch is on, the circuit is closed
and the bulb will light up
30. Series Circuit
The three light bulbs are
arranged in series
Each component is joined one
after the other to form a single
path
Current flows through each
component is the same
31. Series Circuit
If one bulb in a series circuit is
removed or broken, no current
flows
The remaining bulbs do not
light up
Because the circuit is opened
32. Parallel Circuit
Any amount of light bulbs are
arranged in parallels
Divides two or more branches
and has electrical components
in each branch
33. Parallel Circuit
The current from the battery divides
and flows through each branch
If one bulb breaks or removed,
other bulbs on the circuit remain lit
Because the circuit remains closed
34.
35. Formula
The total resistance of two or
more resistors connected in
series is given by simply adding
the individual values of the
resistors to find the total sum
(RTOT):
36. Formula
For resistors in parallel:
To calculate the total resistance
of a circuit that involves parallel
resistors the following formula
can be used.
40. Electric Current
Flow of electric charges
This flow of electrons in one
directions in a circuit is called
an electric current
Electrons require energy in
order to move
Energy come from the electric
cell in the circuit
Electric cell has two terminals
41. Electric Current
Positive and negative
Pushes electrons out of the
negative terminal and round
the circuit
Flow back to the positive
terminal of the cell
Electrons are not used up only
energy is used up
42. Measuring Electric Current
Ammeter
SI unit for electric current is
ampere (A)
1A = 1000 mA
1mA = 0.001A
Connected in series
44. What is Voltage?
To measure the energy the
electrons receive
An electron can have a large
amount of potential energy at one
point in the circuit
It can also have a low amount of
potential energy at another point
The difference in potential energy
between the two points is known as
voltage
47. Voltmeter
Connected in parallel across
the cell
Has positive (red) terminal and
a negative (black) terminal like
ammeter
Positive terminal connected to
the positive side of the cell
Negative terminal connected to
the negative side of the cell
49. Different voltage for
different electric sources
Different electric cell have
different voltage
In Singapore the main voltage
is 230V
1.5V
9V
12V
50. How are electric cells connected
in electrical appliances?
Electric cells are connected in
series with the positive terminal
of one cell touching the
negative terminal of the next
cell
The total voltage across all the
electric cells is equal to the
sum of the voltages of the
individual cells
51. How are electric cells connected
in electrical appliances?
For example you have electric
cell of 1.5V
If the toy need 9V to work.
You will need six 1.5V electric
cells
53. What is a resistor?
Appliances need to ensure that
the correct size of current flows
to operate properly
To control the size of the
current, electrical components
called resistors are used in the
circuits
55. Fixed Resistors
One fixed resistance
Resistance can be a fraction of
an ohm to thousands of ohms
SI unit is ohms
56. Variable Resistors
Known as rheostat
Vary the resistance in a circuit
Resistance change, the current
also changes
When resistance decreases,
the current increases
60. Arrangement of resistors
Parallel
For resistors in parallel, current
from the electric cell divided
among the resistor
More resistors added more
electrical charges are able to
flow through the resistors at the
same time
Current in circuit increases
Overall resistance of the parallel
circuit decreases
61. Metal with…
Low resistance
Copper and silver
High resistance
Nichrome
63. Effects of Electric Current
Heating effect
Magnetic effect
Chemical effect
64. Heating Effect
Resistance in circuit wires
affects the amount of electric
current flowing
Electric current flows through
the wire, the wire gets heated
up
Electrical energy to heat
energy
65. Heating Effect
Heating element in an
electrical appliance consists of
high resistance wires such as
nichrome
Very hot
Produce more heat
Connecting wires are made of
low resistance materials such
as copper
Less hot
Produce less heat
66. Heating Effect
If resistance wire gets very hot,
light can also be produced
Example: Filament of an
electric light bulb
67. Magnetic Effect
Electric current also produces
magnetic effect
Example: placing wire near
compass needle and let
electric current flow, the needle
will move
68. Magnetic Effect
Electromagnet
Coil of wire usually wound
around a piece of iron
When current flows, it acts like a
bar magnet
If no current flow, the
electromagnet loses its
magnetism
69. Magnetic Effect
Electromagnet
How to make it stronger?
Increase the current in the coil
Increase the number of turns of
wire in the coil
Winding the coil around an iron
core
72. Formula
The electric current is given by:
I= V / R
Corresponding units:
ampere (A) = volt (V) / ohm (Ω)
This formula is derived from
Ohm's law. Where we have:
V: voltage
I: current
R: resistance
73. Example Problem
What is the Electric Current if
there is 20 volts and 10 ohms
Given:
20 volts-Voltage
10 ohms-Resistance
Unknown:
Electric Current
76. Chemical Effect
Extraction of metals
Solid compound of the metal is
heated until it melts
An electric current is then
passed through the molten
compound
Molten compound break down to
give the metal
78. ADVANTAGES
It is transportable over long
distances
It is silent
It can be used produce magnetic
fields, which can be used to propel
motors
It is very transformable
79. ADVANTAGES
It is very fast, virtually the speed
of light
It can be used to produce other
forms of radiant energy, such as
radio waves, microwaves,
radiant heat and light
EDIT: You can store it for use
later
81. DISAVANTAGES
It can kill you
We become dependent on it
We use other dirtier forms of
energy (nuclear, fossil fuels) to
produce it
There is growing concern that
the magnetic fields around
transmission lines may be
unhealthy
83. Outlets
Check the Outlets that have
loose-fitting plugs which can
heat and lead to fire
Replace any missing or broken
wall plates
Place the safety covers on all
unused outlets that are
accessible to children
85. MAGNET
The black metallic that has the
property of contracted iron is
called loadstone
The natural force of attractive
pieces of iron is called
magnetism
Loadstone was later known
magnet for the magnetic
property
86. Magnet
Thales was the Greek
philosopher who first discovered
the magnetic property of
loadstone
89. Coil
Coil – A number of turns of wire
wound around a
core to produce magnetic flux
(an electromagnet) or
to react to a changing magnetic
flux (an inductor).
Electromagnet – A magnet
consisting of a coil
90. Coil
wound on a soft iron or steel
core. When current is
passed through the coil, a
magnetic field is generated
and the core is strongly
magnetized to concentrate
the magnet field.
91. Left-hand rule
If the fingers of the left hand are
placed around the wire so that
the thumb points in the direction
of the electronic current flow, the
finger will be pointing in the
direction of the magnetic field
being produced by the
conductor
93. Electromagnetic induction
The voltage produced in a coil due to
relative motion between the coil and
magnetic lines of force.
Faraday’s Law – When a magnetic
field cuts a conductor, or when a
conductor cuts a magnetic field, an
electric current will flow in the
conductor if a closed path is
provided over which the current can
circulate.
94. Electromagnetic induction
Lenz’s Law – The current induced in a circuit
due to a change in the magnetic field is so
directed as to oppose the change in flux, or
to exert a mechanical force opposing the
motion.
Weber – A unit of magnetic flux. One weber
(10^8 maxwells) is the amount of flux that,
when linked with a single turn of wire for an
interval of one second, will induce an
electromotive force of one volt.
98. EINSTEIN
Electricity and magnetism were
long thought to be separate
forces. It was not until the 19th
century that they were finally
treated as interrelated
phenomena. In 1905 Albert
Einstein’s special theory of
relativity established beyond a
doubt that both are aspects of
one common phenomenon.
99. EINSTEIN
At a practical level, however,
electric and magnetic forces
behave quite differently and are
described by different equations.
Electric forces are produced by
electric charges either at rest or
in motion. Magnetic forces, on
the other hand, are produced
only by moving charges and act
solely on charges in motion.
100. FARADAY
He discovered in work that
forms the basis of electric power
generation. Conversely, a
changing electric field produces
a magnetic field,
Electric phenomena occur even
in neutral matter because the
forces act on the individual
charged constituents
