Electricity
Year 9 Science
What is Electricity??
• Electricity is one of many forms of energy.
• Electricity powers your laptop, iPad, hairdryer, TV &
lights up your house at night.
• What makes electrical energy so useful is that it can
be transformed into other forms of energy such as
heat, light and sound.
Electric Charge
• Everything made up of atoms (protons, neutrons and
electrons)
• Located in nucleus of atoms (protons & neutrons)
• Spinning on outside is electrons
• Protons & electrons are electrically charged; protons
carry a POSITIVE charge and electrons carry a
NEGATIVE charge.
Electric Charge
• Neutrons= neutral.
• Overall atom should be neutral because PROTONS = ELECTRONS
• However sometimes electrons can be knocked off or added to an
atom.
• This gives the atom an overall charge- known as an ion.
• If electrons removed = then the ion has MORE protons meaning it
is a positive charge
• If electrons added= MORE electrons meaning it is a negative charge
Static vs Current
• Electricity is a type of energy that can build up in one
place or flow from one place to another.
• When electricity gathers in one place it is known
as static electricity (the word static means something
that does not move)
• Electricity that moves from one place to another is
called current electricity.
Static Electricity
• Is the build-up of electric charge on a surface.
• This build- up commonly occurs because of surface rubbing
against another surface
• Example – when you rub a balloon against your jumper (it will
stick to you)
• https://www.youtube.com/watch?v=yc2-363MIQs
Static Electricity
• Rubbing can cause electrons to be rubbed off one
surface, charging it positive (if it has lost negative
electrons).
• These electrons are transferred to the other
surface, charging it negative.
• Static charge usually leaks away after some time.
Current Electricity
• An electric current is a flow of electrons which
flow through wires and components.
• These moving electrons carry energy that is
transformed into other forms of energy as the
electrons pass through things like light globes
(transforming electrical energy into light)
Which direction does the current flow?
•Current flows from NEGATIVE to
POSITIVE
Simple electric circuits
• Electrons travel along a path to deliver their energy;
• This path is called an electric circuit.
• Electric Circuit components:
• An energy source/ cell (usually a battery)
• An energy user (usually a light globe)
• Wires to connect everything
• Switch to break circuit, turning it off/on.
Circuit Diagrams
• Simplified version of real circuit
• A torch is an example of a simple circuit.
• Draw on board (figure 6.1.6 pg 222)
Class work
• Pearson 9 Chapter 6.1
• Page 223
• Questions 1, 3, 6,7,8, 9,11,14
Measuring Electricity
6.2
Current Electricity
• Recap- an electric current is formed whenever
charge flows from one spot to another.
• In an electric circuit, this flow of charge is made up
of electrons moving along wires.
Measuring Electricity
• Why would we need to measure electricity??
• Electricians & Electrical engineers need to ensure
that the electric circuits within our homes are
SAFE and are able to carry out the job they are
required to do.
Current
• Current can be DIRECT (DC) or ALTERNTAING (AC)
• DC- electrons all flow in same directions e.g battery
• AC- electrons shuffle back and forth along the wire e.g power points
Electric Current
• Electric current is measured using an ammeter.
• An ammeter measures the amount of charge
that flows through it every second.
• The current is HIGH if a lot of charge flows
through it in one second, and LOW if only small
amount flows through.
• The unit used to measure current is ampere
(unit symbol A), often we say measured in
‘amps’
Connecting up an ammeter
• Electrons must pass through the
ammeter for a charge to be detected
• Therefore the ammeter need to be in
line with the rest of the circuit’s
components.
• This arrangement is known as being in
series
Voltage
• Voltage is a measure of the amount of energy/ force needed for the electrons
to flow through an electric current
• VOLTAGE is measured using a Voltmeter
• Voltage= high if electrons supplied with lots of energy
• Voltage= low if electrons lack energy
• Voltage = zero then battery is dead
• Unit used to measure Voltage is VOLTS (V)
Connecting up a voltmeter
• A voltmeter compares the energy of
electrons before and after they pass
through a component (such as a light
globe)
• For this reason, voltmeters are
connected up in parallel.
• This means they are not part of the
circuit itself, but instead attach across
the component being measured.
Voltage Supply
• Each energy source has its own Voltage.
• In AUS, power points supply 240V to the electrons in any circuit
plugged in to them.
• Sometimes a transformer is used to reduce the voltage from a
power point to a more manageable voltage.
• Example- 240V from power points, but laptop only needs 19V to
charge.
Batteries
• Excellent source of portable electrical energy
• Batteries are made of small cells or ‘mini batteries’
• Cells can be classified as:
• - wet cells
• -dry cells
• -photovoltaic or solar cells
Batteries
• Wet cell- has conducting electrodes submerged in liquid
electrolyte.
• Electrodes- are rods, sheets or plates made of a metal or
some other conducting material like graphite.
• Electrolyte- solution that conducts electricity.
Batteries
• The small, portable batteries used in
torches etc are dry cells.
• Compact because have one electrode
wrapped around another
• They don’t leak- conducting paste
instead of liquid.
Batteries
• Photovoltaic cells (or solar cells) convert solar
energy directly into electrical energy.
• Energy in sunlight knocks electrons off silicon
crystals within the cell. Electrons then move
away from the crystal, forming an electrical
current.
Resistance
• Electrons lose energy as they pass through a component
such as light globe
• This results in voltage drop across the component.
• Voltage drop depends on the RESISTANCE of the
component.
Resistance
• As electrons pass through the wires of an electric
current, their path is restricted by little atoms in the wire.
• This restriction or difficulty is known as resistance.
• Resistance measures how difficult it is for an electric
current to flow through a material or a component.
• High resistance- difficult for electrons to pass through
• Low resistance- easy for electrons
Resistance
• Resistance of a wire depends on many things:
• Type of material
• Length of wire
• Thickness of wire
Measuring Resistance
• Measured using the unit Ohm.
• The unit symbol for ohms is known as omega.
• Can be measured by a multimeter.
• Resistors:
Ohms Law
• Ohms Law states that ‘V’ is directly proportional to ‘I’
• V= Voltage
• I= Current
Calculations using Ohm’s Law
•R= V/I
• R= Resistance
• I= Current
• V= Voltage
Ohm's Law is a formula used to
calculate the relationship
between voltage, current and
resistance in an electrical circuit.
Conductors vs Insulators
• Metals are conductors- this means an electric current
will pass easily through them.
• E.g copper is excellent conductor (low resistance & no
energy lost)
• Some materials have high resistance that block
electric current completely. These materials are called
insulators.
• Examples include rubber, plastics, wood, glass and
ceramics.
Class work
•Chapter 6.2 page 233
•Questions 1-8,10,17
Circuits
6.3
Video!
• https://www.youtube.com/watch?v=zSSkZ9F7Bng
Series Circuits
• In a series circuit, all the components of
the circuit are connected up one after
another to form a single loop.
• Easiest circuit to connect up
• Three identical globes are connected in
series in the diagram.
• Both globes have same current flowing
through them (e.g. 3V)
Series Circuits
• 6 V leaves the battery
• This 6V of energy is shared
2V
equally between the globes (e.g
2V each)
2V
• Each globe uses 2V worth of
energy each
6V
2V
Series Circuit
• Series circuit must have same current flowing through them but
must split the voltage equally
• The globes cannot be controlled individually (a switch would turn
them all on or off)
• Current slops flowing around them if any of the globes ‘blow’
• Adding more globes makes them glow duller than before.
Connecting up an ammeter
• Electrons must pass through the
ammeter for a charge to be detected
• Therefore the ammeter need to be in
line with the rest of the circuit’s
components.
• This arrangement is known as being in
series
Parallel Circuits
• A parallel circuit has a
number of branching
circuits, each branch having
its own components.
• The current leaving the
battery splits into two, with
half going down each
branch.
Parallel Circuits
• An individual electron can only
pass through one globe and so
its used ALL of its energy in
that one globe.
• Therefore each globe will
receive the full 6V supplied by
the battery.
6V
6V
6V
6V
Parallel Circuits
• Have many advantages over series circuits
• Each branch can have its own switch- each globe can be
switched on/off independently from each other
• Only one branch is affected if a globe ‘blows’
• Adding extra globes does not affect brightness
Connecting up a voltmeter
• A voltmeter compares the energy of
electrons before and after they pass
through a component (such as a light
globe)
• For this reason, voltmeters are
connected up in parallel.
• This means they are not part of the
circuit itself, but instead attach across
the component being measured.
Combination Circuits
• Figure 6.3.5 bottom of Page 240 Pearson 9
• Sometimes circuits have some of both components.
Household wiring
• Electrical wiring in a house is one large parallel circuit,
with each light or power point located on its own branch
with its own switch.
• Each receives the full supply voltage of 240V, allowing
each to work at its full power.
• Diagram 6.3.6 page 241 – parallel circuit… allows
everything to be controlled independently
Household wiring continued
• Electrical cables; three different ones
• Active wire- (coated in brown plastic)
carries current to a power point
• Neutral wire- (blue) carries current away
• Earth wire (coated in green and yellow
plastic)- connects the power point and
any metal part of appliances to the earth
beneath you.
• Figure 6.3.7 page 241 (bottom)
Household wiring continued
• 240V can be deadly if the current finds a way out of the wires
and through you.
• If part of a circuit breaks, this allows the wire to touch the
casing or switch
• You can then become part of the wiring and current will flow
through you instead of down the neutral wire!
• The result would be an electric shock or possibly
electrocution (death by electricity)
Electrical Safety
• Most circuits have a device that
breaks the circuit if a faulty
appliance allows an abnormally
high current to flow.
• Abnormally high currents cause
wires to heat up rapidly.
• This might melt the plastic
coatings and then set fire to the
dust trapped within the wires in
walls and roof space.
Electrical Safety
• Fuses- wire of hire resistance & low melting point
which causes it to melt if too much current flows
along it.
• Melting breaks the circuit and stops the current.
• Circuit breakers- switch that is activated by
higher-than-normal current. Generally happens
when there is a short-circuit.
• Safety switches- found on switchboards- when
safety switch detects leaks it breaks the circuit
within 0.3 seconds.
Class work
•Chapter 6.3 page 245
•Questions 1-9
Ohms Law &
Calculations
Pearson 9 Chapter 6
Ohm's law magic
triangle:
Resistance = Voltage/Current
R= V/I
Voltage= Current x Resistance
V=IxR
Current= Voltage/Resistance
I=V/R
Ohms law:
Defines the relationship between voltage, current
and resistance.
These basic electrical units apply to direct current,
or alternating current.
Ohm’s Law is the foundation of electronics and
electricity.
Voltage measured in volts,
symbolized by the letter "V".
Current measured in amps,
symbolized by the letter "I".
Resistance measured in ohms,
symbolized by the letter "R".
Let's see how these equations might work to help us analyze
simple circuits:
If we know the values of any two of the three
quantities (voltage, current, and resistance) in
this circuit, we can use Ohm's Law to determine
the third.
milliamp or just mA
Practice!!
• Try the worksheets on your own!
• Will go through and get students to put answers on the board 
Electromagnets, Motors &
Generators
Pearson 6.4
Magnetism
• Around a permanent magnet is an invisible force field called
a magnetic field.
• This field exerts force on:
• Materials containing iron, cobalt or nickel
• And other magnets nearby.
• Each magnet has a north pole (N) and a south pole (S).
• Unlike poles such as N/S attract whereas poles that are the
same will repel such as S/S or N/N.
Field lines
• The direction & strength of a magnetic field is show by its field
lines.
Electromagnetism
• HOW DOES ELECTRICITY CREATE MAGNETISM?
• Each electron is surrounded by a force called an electric field.
When an electron moves, it creates a second field—a magnetic
field.
• When electrons are made to flow in a current through a
conductor, such as a piece of metal or a coil of wire, the
conductor becomes a temporary magnet—an electromagnet.
• When electricity has caused magnetism, this is known as
electromagnetism.
Electromagnets
• Solenoids are powerful electromagnets made from an iron rod wrapped in
coils of electric wire.
• When electricity flows through the wire, it turns the iron rod into a powerful
magnet. When the electricity is switched off, the iron rod stops being
magnetic.
• Used in hotel door locks, MRI machines, speakers, microphones, power
plants, TVs and cars.
Solenoids
Electric Motors
• One of the important applications of electromagnetism is the electric motor.
An electric motor converts electrical energy into physical movement. Electric
motors generate magnetic fields with electric current through a coil. The
magnetic field then causes a force with a magnet that causes movement or
spinning that runs the motor.
Electric motors are used in all sorts of applications. There are several electric
motors inside your computer including one to turn the fan, one to open and
shut the CDROM drive, and one to operate the hard drive. Also found on the
back of fans causing it to spin.
Electric Motors
• In electric motors, current is passed
through a coil. The magnetic field it
produces interacts and causes the coil
to spin.
•
You can see in the diagram a currentcarrying coil is placed within a
magnetic field of a permanent
magnet. The coil spins because of the
forces on it.
Generators
• Electricity available from batteries is great and useful
for portable devices. However generators may be used
to power more larger industry related devices and
machinery.
• A generator uses electromagnetism to generate
electricity.
• Turbines are an example of a large-scale electricity
generator. Turbines need to be spun at high speeds,
and different methods can be used to spin them.
• Dynamos is a small generator that are used to power
the front lights on bicycles; (generators current
through headlights)
Different ways to turn the turbines:
• Wind, moving water or steam can be used
• Moving water:
• Hydro-electricity is generated by water falling
onto the blades of the turbines, which causes
them to spin.
• Wave power uses the regular swells of the
ocean to rock the turbines back and forth
• Tidal power: uses the massive flows of water
from the twice-daily changes of the tides to
spin turbines.
Steam:
• Power plants boil water and change it into high pressure steam, and
this steam then spins the turbines.
• Many different ways this can occur: FIGURE 6.4.3 page 257
talks through all the different methods of turning a turbine (plus the
advantages + disadvantages of each)
• Example: burning fossil fuels such as coal or gas (easy + cheap way of
generating steam and therefore electricity) but gives off huge amounts
of CO2.
AC/DC
• Batteries and solar sells produce DIRECT CURRENT (DC)
• Generators, dynamos and turbines produce ALTERNATING CURRENT (AC)
• Comparing AC with DC table page 258 (copy into
books)
• Most power plants produce AC voltages of around 20000 V
• Transformer- can reduce the AC voltage OR can step it up and increase it if
need be (power plants)
Classwork/HW (final chapter yay!)
• Review Questions Chapter 6.4 page 261
• Questions 1-10
• Question 12 (refer to figure 6.4.2 page 255)
• Questions 17+18