ELECTRICITY AT WORK
Chapter 10.2 & 10.3
Year 9 Science
By the end of this lesson you should be able to:
Have an understanding of how electrical
circuits work, how the energy is transferred
and what the symbols stand for
Understand the electrical charge of an object
can be positive or negative
Understand what static electricity is and how it
is caused
LESSON OBJECTIVES:
A bolt of lightning is clear evidence
that electrical energy can move from
one place to another. But to make
energy useful it needs to be controlled.
When you switch on a television, a
computer or an mp3 player you are
completing a pathway along which
electrical energy flows. The pathway is
called an electric circuit, in which
electrical energy is transformed and
used for lighting, heating, cooling and
much, much more.
ELECTRICITY IN TRANSIT
electric circuit: a path for electrons to follow,
consisting of a power supply, one or more loads, and
conductors joining the power supply and loads
The movement of electrical energy from one place to
another, whether rapidly in the form of lightning or
more slowly in an electric circuit, depends on the
movement of electric charge.
Electric charge can be positive or negative
PATHWAYS FOR ELECTRICITY
Think back to Year 8 Science:
The centre of the atom is the nucleus
Protons are positively charged, electrons are negatively charged
Any particle or substance that has more protons than electrons is
said to be positively charged. Any particle or substance that has
more electrons than protons is said to be negatively charged. Any
particle or substance that has equal amounts of positive and
negative charge is said to be neutral. The term ‘uncharged’ is also
used to describe neutral particles or substances.
WHAT IT MEANS TO BE CHARGED
The electric charge that builds up in
clouds and objects such as plastic rulers
and balloons is called static electricity;
that is, it is not moving.
When enough static electrical energy
builds up it can move very quickly, as it
does when lightning strikes or when you
get a small electric shock when you
step out of a car or touch a metal door
handle.
STATIC ELECTRICITY
 Static
electricity is the result of an imbalance between
negative and positive charges in an object.
 These
charges can build up on the surface of an
object until they find a way to be released or
discharged.
 An
electrical charge is created when electrons are
transferred to or removed from an object. Because
electrons have a negative charge, when they are
added to an object, it becomes negatively charged.
When electrons are removed from an object, it
becomes positively charged.
HOW DOES STATIC ELECTRICITY WORK?

The rubbing of certain materials against one another can
transfer negative charges, or electrons. For example, if you
rub your shoe on the carpet, your body collects extra
electrons. The electrons cling to your body until they can
be released. As you reach and touch your furry friend, you
get a shock. Don’t worry, it is only the surplus electrons
being released from you to your unsuspecting pet

When you rub a balloon against your clothes and it sticks to
the wall, you are adding a surplus of electrons (negative
charges) to the surface of the balloon. The wall is now
more positively charged than the balloon. As the two
come in contact, the balloon will stick because of the rule
that opposites attract (positive to negative).
FOR EXAMPLE
All electric circuits consist of three essential items:
a power supply to provide the electrical energy
a load (or loads) in which electrical energy is
converted into other useful forms of energy
a conducting path that allows electric charge to flow
around the circuit.
ELECTRIC CIRCUITS
The batteries (cells) used in torches and many other
devices store chemical energy in the substances inside
them. The chemical energy is transformed into
electrical energy when a chemical reaction takes
place inside the cell.
The electrical energy that is used when you turn on a
light switch or an appliance connected to a power
point comes from a power station.
WHERE IT ALL BEGINS
The flow of electric charge is called electric current. It
is a measure of the amount of electric charge passing
a particular point in an electric circuit every second.
Even though the electric current in wires and most
electrical devices is caused by the flow of negatively
charged electrons, electric current is defined as the
direction of the movement of positive charge. The
electric current is said to flow through the circuit from
the positive terminal of the power supply to the
negative terminal.
CURRENT AND VOLTAGE
Voltage is a measure of the amount of electrical
energy gained or lost by electric charge as it moves
through the circuit.
Voltage is also known as potential difference because
it measures a change in the potential (stored) energy
of charge as it moves between one place and
another.
When electric charge moves through a circuit, it gains
electrical energy as it passes through the power
supply. It loses the same amount of energy as it passes
through the rest of the circuit. That is, the voltage gain
across the terminals of the power supply is equal to the
total voltage drop across the rest of the circuit.
CURRENT AND VOLTAGE
The load in an electric circuit is an energy converter. It
is here that most of the electrical energy carried by
electric charge is transformed into useful forms of
energy such as light, heat, sound and movement.
In a simple torch the load is the filament, a coiled
tungsten wire inside the globe. The filament glows
brightly when it gets hot.
WHERE THE ACTION IS
The electrical energy provided by batteries and
power outlets is transformed into other forms of energy
only when the conducting path is complete.
A switch in an electric circuit allows you to have
control over whether or not the conducting path is
complete.
SWITCHED ON
A complete conducting path allows electric charge to flow
through the circuit.
In an efficient electric circuit, most of the electrical energy
provided by the power supply is transformed in the load. However,
some of the electrical energy is transformed in the conducting path,
heating the path and its surroundings.
The conducting paths in the electric circuits in appliances are
usually made of metals such as copper so that they have
little resistance to the flow of electric charge.
COMPLETING THE PATH
Make a glossary for:
-
Electric circuit
-
Electric charge
-
Electric current
-
Voltage
-
Filament
Complete questions 1-6 in Chapter 10.2 of textbook
TEST YOUR KNOWLEDGE:
Many battery-operated devices use more than one
battery. In torches, mp3 players and cordless power
tools, two or more batteries are connected in series.
They are connected end-to-end as shown in the
diagram in this section. It is important to ensure that
the positive end of one battery is connected to the
negative end of the other.
Diagrams of electric circuits need to be drawn so that
people all over the world can read them. Circuit
diagrams use straight lines for connecting leads and
symbols for other parts of circuits.
CIRCUIT DIAGRAMS: A COMMON
LANGUAGE
The power supply of a torch usually consists of two or more 1.5-volt
batteries connected in series. When two 1.5-volt batteries are
connected in series, the total voltage is 3.0 volts. Twice as much
electrical energy is available to move the electric charge around
the circuit.
The load in a torch circuit is the globe. When the switch is closed,
electric current flows around the circuit. As electric charge passes
through the globe, its electrical energy is released as heat in the
filament. The filament is the coiled wire inside the globe. It is made
of the metal tungsten and glows brightly when it gets hot.
When the switch is open, the metal strip does not make contact
with the globe and the circuit is not complete
THE TORCH CIRCUIT
What do all the symbols mean?
Go into your textbook and check
CIRCUIT DIAGRAM FOR A TORCH
Complete questions 1-4 on Chapter 10.3 in textbook
TEST YOUR KNOWLEDGE: