Transcript Electricity Energy - Ch 6 - TCC-Yr9

Electricity Energy
CH 6.1, 6.2, 6.3 AND 6.4 STARTING AT PAGE 183
Teacher Resources - S:\Science\7-12 wikis
Introduction Video on Electricity - BBC Bitesize
Overview of Electricity - BBC Bitesize
Ch 6.1 Electricity - quizlet
Electric circuit symbols - quizlet
Ch 6.2 Measuring electricity - quizlet
Ch 6.3 Practical circuits - quizlet
Ch 6.4 Electromagnets, motors and generators - quizlet
Cool UK - electromagnetism and motors
BBC Bitesize - Overview of Electromagnetism
BBC Bitesize - Video - motors and electromagnetism
Ch 6.1 Simple circuits
Electrical Charge

Protons are positive

Neutrons are neutral

Electrons are negative
Static electricity
Statistic electricity – the build up of electrons on a surface. Usually
due to one surfaces rubbing against another surface.

Electrons are removed from one surface (becomes positive)
and

Electrons are added to the other surface (becomes negative)

This charge may leak slowly into the surrounding atmosphere,
or

The electrons may jump across a gap and discharge in one
go, releasing light, heat, sound and kinetic energy – a spark.

Lightning is the build up of static charge in the atmosphere
that then jumps to the earth, a building or another cloud.

Static Electricity - Interactive page 184
Current electricity
Current electricity is made up of a continuous and uninterrupted flow
of electrons

The moving electrons have energy that can be converted into other
forms of energy – eg light, heat, sound, magnetism

A circuit usually requires the following components: power source,
wires to connect all elements of the circuit, an energy user (light,
buzzer, amplifier, element etc) and a switch.

Each component has specific symbol to represent it in diagrams

Current Electricity – Videos page 185
Circuit components symbols
Circuit components memory game - Interactive page 185
Circuit diagram
Circuit diagrams
Torch circuit diagrams
Series & parallel circuits
There are two types of circuit we can make, called series and parallel.

The components in a circuit are joined by wires.

if there are no branches then it's a series circuit

if there are branches it's a parallel circuit
Series circuits

In a television series, you get several episodes, one after the other. A
series circuit is similar. You get several components one after the
other.

If you follow the circuit diagram from one side of the cell to the
other, you should pass through all the different components, one
after the other, without any branches.
Parallel circuits

In parallel circuits different components are connected on different
branches of the wire. If you follow the circuit diagram from one side
of the cell to the other, you can only pass through all the different
components if you follow all the branches. Blue
Review Questions p 186
1 Charges of:

a an atom = neutral (0)

b a proton = positive (+)

c a neutron = neutral (0)

d an electron = negative (–).
2 a In an atom, the number of protons = the number of electrons.

b In a positive ion, the number of protons > the number of electrons.

c In a negative ion, the number of protons < the number of
electrons.
3 When a spark jumps across a gap, energy is released as light, and
some is released as light and heat (and perhaps sound).
5 Electrons are the charged particles that carry an electric current
through a circuit.
An electric circuit needs:

an energy source

an energy converter

wires.

A circuit usually has a switch too, although this is not essential.
6 Examples of:

a an energy supplier: battery, generator, dynamo

b components that use electrical energy: light globe, heating
element, motor.

Ch 6 Review Ans.docx
Ch 6.2 Measuring amps & volts
Current

Current is a measure of how much electric charge flows through a
circuit. The more charge that flows, the bigger the current.

Current is measured in units called amps. The symbol for amps is A.
For example, 20A is a bigger current than 5A.
Measuring current

A device called an ammeter is used to measure current. Some
types of ammeter have a pointer on a dial, but most have a digital
readout. To measure the current flowing through a component in a
circuit, you must connect the ammeter in series with it.
Ammeters are placed in series
Voltage
Voltage

Voltage is a measure of the difference in electrical energy between
two parts of a circuit. The bigger the difference in energy, the
bigger the voltage.

Voltage is measured in volts. The symbol for volts is V. For example,
230V is a bigger voltage than 12V.
Measuring voltage

Voltage is measured using a voltmeter. Some types of voltmeter
have a pointer on a dial, but most have a digital readout. To
measure the voltage across a component in a circuit, you must
connect the voltmeter in parallel with it.
Practical measurement in circuits
1.
Go to S:\Science\7-12 wikis and open up the circuit construction app and
the ‘Measuring Current in series and parallel circuits PhET - Ohm's Law Mr
Wust’ document. You have 2 minutes to complete the tasks.
2.
Open ‘Ch 6 Worksheet 1 Circuit Calcs’ from S drive and complete the
calculations. This is available for download from the Pearson text book on
page 190
3.
Page 182 Interactive Electrical Terms matching items.
Ch 6.2 Wet cells, dry cells and
photovoltaic cells

Wet cell - 2 different metal
electrodes and an electrolyte
solution eg car battery - acid
and metal electrodes

Dry cell - contain a conducting
paste, and electrodes - doesn't
leak

Photovoltaic Cell - contain
semi-conducting silicon
crystals - sunlight knocks
electrons off the crystal and
they are used to create a
current.
Resistance
V = IR

As electrons pass along a wire, their progress
is restricted by the atoms they encounter.
Energy is lost as heat or light. Too much
resistance and the wire will melt creating a
fire.
Factors affecting Electrical Resistance

1 - type of material - metals provide little
resistance.
2 - as the length of the wire increases, then so
does the resistance.
3 - as the diameter of the wire increases, the
resistance decreases.
Conductors and insulators
Conductors

Metals are conductors - they offer very little resistance. Copper and
Aluminium are the better ones – graphite (carbon).
Insulators

Have such a high resistance, that no current is possible - rubber,
plastics, wood glass and ceramics.
Ch 6.3 Practical Circuits
Series Circuit

all of the components are in a single simple loop or circuit - if a
globe burns out the circuit fails. Adding more globes reduces their
brightness. Each globe shares the voltage.
Parallel Circuit

the circuit has a number of independent branches that can have
individual switches. A globe failing in one branch does not affect
the other branches. Brightness is maintained as more globes are
added. Each branch receives the full voltage.

Page 200 video and Page 201 comparing circuits and bulb
brightness.

House current - Extremely Dangerous. Parallel circuit - 240 V and 50
cycles per second AC (alternating current) flows in both directions.
Likely to kill.

Batteries current - Dangerous. DC (direct current) - only flows in one
direction.

Active wire - Brown plastic - carries current to the power point

Neutral wire - Blue plastic - carries current away from the power
point

Earth wire - Green/Yellow plastic - connects the power point and
any metal part of the appliance to the ground - a dangerous stray
current will go to the earth, rather than through you.

Fuse - a wire of high resistance and low melting point - if the current
becomes too high, it melts and breaks the circuit. Difficult to reset.
Found in older homes.

Circuit breaker - is a switch that is activated by higher than
allowable current - it flips off automatically - easy to reset.

Safety switch - also known as an RCD (residual current device)
found in all modern home power boards. Monitors the current into
and out of the house - these should always be equal. If they are not
equal, then it is likely the current is leaking out from a faulty
appliance or via a person - reacts in 0.03 sec - you still get a shock
but hopefully not enough to kill you.
Ch 6.4 Electromagnets, motors and
generators

Blue and Aqua here

Magnetism an invisible field that exerts force
on iron, cobalt or nickel.

Electromagnetism a magnetic field produced
by an electric current

2 PhET magnet and solenoid simulations

Cool UK - electromagnetism and motors

Solenoid
- a looped current
carrying coil of wire

Electromagnet - a magnet
created by an electric current can be controlled by varying
the current ON-OFF. eg include
junk yard, iPod, phone,
speakers, microphone, circuit
breakers
Electric motors
Electric Motor - a current carrying coil of wire will
spin in the field of a permanent magnet - this is
the opposite to a generator.
Generator - a coil of wire is made to spin in the
field of a permanent magnet - this produces an
electric current - this is the opposite to an
electric motor
Turbine - a large generator - the coil is kept still
and the magnet spins around it eg bicycle light
generator, steam, wind turbines, hydro-electric,
wave power and tidal power.
Page 211 video on wind farms
AC/DC and Transmission

AC - Alternating current - the electrons shuffle back and forwards
at 50 cycles per second or 50 Hertz. Can generate more power,
easier to transmit and its voltage can be changed by transformers.
Has to be converted to DC to be stored.

DC - Direct current - the electrons flow in one direction only. Only
suitable on small appliances. Easy to store

Transmission - Very high voltage and very low current eg 500 000 V.
This reduces the lost energy. However home users require a much
lower voltage - so transformers are used to step voltages up or down
as required.

Worksheet – Snowy Mountains Scheme page 213
Revision checklist

Chapter Revision Test from the Resources Tab of the Textbook.

The Worksheets 6.1 and 6.2

Unit Review Questions x 4

Prac write ups