Download Nat 4-5 Unit 2 Section 2 pupil notes - update

Turnbull High School
Physics Department
S3 Physics
Unit 2 :- Electricity and Energy
Section 2:
Electricity Generation and
Electromagnetism
Name:
Class:
1
National 4
Unit 2 Section 2
By the end of Unit 2 Section 2 I can:
1. Describe some methods of energy conservation
2. Compare advantages and disadvantages of renewable and nonrenewable energy supplies
3. In simple terms describe how electricity is generated
4. Compare a variety of types of power station and methods of
generating electricity
5. State that the region surrounding a magnet is called a
magnetic field and describe some factors that could affect
the magnetic field
6. State that a magnetic field exists around a current-carrying
wire and describe some factors that could affect the
magnetic field around the wire
7. Give two examples of practical applications which make use of
the magnetic effect of a permanent magnet or an
electromagnet.
2
Supply and Demand
Conserving (Saving) Energy
• The more energy we use, the more money it costs us.
• Where we will get energy from in the future is very
uncertain.
• For these reasons, it is important that we conserve
(save) energy - We should use as little as possible
and try not to waste it.
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Non-Renewable Sources of Energy
Fossil fuels and nuclear fuels (used in nuclear power stations) are
non-renewable sources of energy - Their reserves are finite.
Finite means _______________________________________
_________________________________________________
_________________________________________________
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Experiment 1
Your teacher will demonstrate some examples of how renewable
energy sources can produce electricity.
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Generation of Electricity
In a power station, electrical energy (electricity) is generated
when large metal turbine blades are turned by something hitting
them. The turning turbine blades turn a generator which changes
the kinetic (movement
movement) energy to electrical energy.
The turbine blades and generator are the size of a large room.
The energy change in the generator is:
_________ Energy
to
________Energy
Different types of power station turn the turbines in different
ways.
Your teacher
eacher will now show you a power point presentation on
power stations using “Footprints Physics”.
Thermal Power Stations
These burn f _ _ _ _ _ fuels. The h _ _ _ energy released boils
water in a boiler.
S _ _ _ _ is produced and this hits the t _ _ _ _ _ _ blades,
blades
making them t _ _ _..
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Nuclear Power Stations
In a n _ _ _ _ _ _ r _ _ _ _ _ _, nuclear reactions produce h _
_ _ energy which boils water in a boiler. S _ _ _ _ is produced
and this hits the t _ _ _ _ _ _ blades, making them t _ _ _.
These do not boil water to produce s _ _ _ _.
Hydro-Electric Power Stations
Water falls from a great height down a
dam and hits t _ _ _ _ _ _ blades at the bottom of the dam,
making them t _ _ _.
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Tutorial 1: Methods of generating electricity
In Scotland, a range of different methods are used to generate
the electricity that we use to power our homes, schools and
offices.
Percentage of electricity generated by different sources in 2010
Historically, fossil fuels (coal, oil and gas) were the main sources
of fuel used to generate electricity. These had the advantage of
being cheap and plentiful. However, fossil fuels are nonrenewable, that is there is a limited supply which is running out.
When that has been used up no more will be produced. Fossil
fuels are also polluting, by burning them greenhouse gases are
released which contribute to global warming.
From the graph shown you can see that nuclear power stations
provide a significant amount of the electricity we use in this
country. Nuclear fuels such as uranium are also non-renewable,
but they have the advantage that they are non-polluting. A
significant downside to nuclear power is that it leaves behind
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radioactive waste which can take thousands of years to reach
safe levels.
As both these types of fuels are non-renewable, in recent years
people have started to look at renewable sources of energy.
Unlike non-renewable sources,
A hydro-electric power station stores
water behind a dam high on a hill. This
water is then allowed to run down
pipelines to turn turbines, which then
turn the generators to produce the
electricity. Hydro-electric power stations are non-polluting;
however they can only be used in certain areas and can cause
damage to the local environment.
Wind turbines are becoming increasingly
popular as they are also renewable and nonpolluting. However these can only produce
electricity when the wind blows.
Scotland is also well placed to make use of
tidal generation. However it is less well suited
to use of solar cells. One source which may be used more often
in the future is geo-thermal. This is already used widely in
Iceland. Cold water is pumped underground where it is heated by
the rocks below the Earth’s surface. At present this process is
expensive and relatively inefficient.
Some countries are making more use of biomass. This is where
crops are planted then refined to make a fuel such as ethanol.
This is controversial as it reduces the area of land available to
plant crops to feed people.
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©The Scotsman Publications
Ltd. Licensor www.scran.ac.uk.
renewable sources will not run out.
Questions
1.
Make a table separating the sources of energy mentioned in
the passage into renewable and non-renewable
non renewable sources.
Non-Renewable
Renewable
2.
Renewable
Give an advantage and disadvantage for each energy source
mentioned.______________________________________
______________________________________
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3.
Why is Scotland a good place to have hydro-electric
hydro electric power
stations?________________________________________
________________________________________
_______________________________________________
______________________________________________
4.
Why is Scotland not a good place to rely on solar cells?
_______________________________________________
_______________________________________________
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Electromagnetism
The following three experiments will help you find out about
magnetic fields and that any
a
current carrying wire has a
magnetic field surrounding it.
Experiment 2:
2 Permanent Magnets
What you need: Bar magnet, selection of materials.
• Use a magnet to find which materials shown in the table
below are attracted to it.
Material
Does magnet
attract it
Material
Plastic
Steel
(m/steel)
Iron
Wood
Zinc
Nickel
Bronze
Brass
Cobalt
Glass
Does magnet
attract it
• Take two bar magnets and place them so that the
North Pole of one faces the North
Nort Pole of the other - note
what happens..
________________________________
_____________________________________________
_______________
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• Repeat step 2 for different combinations of poles facing
each other and note what happens.
_______________________________________________
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There are _____ magnetic materials - _____, _____, _______
and _______.
A North Pole repels a ______ pole.
A South Pole repels a ______ pole.
A North Pole __________ a South Pole.
_____ Poles attract. _______ Poles repel.
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Experiment 3: Electromagnetism
What you need: Bar magnet, iron filings, wire, d.c. supply,
plotting compass.
• Take a magnet and hold it near some iron filings - note
what happens.
_______________________________________________
_______________________________________________
• Connect the wire to the power pack. Switch on and note
what happens when it is placed near the iron filings.
_______________________________________________
_______________________________________________
_______________________________________________
• Place the plotting compass on the desk. Hold a magnet
above it and at right angles to the direction of the compass
needle - note what happens.
_______________________________________________
_______________________________________________
_______________________________________________
• Connect the wire to the power pack. Hold the wire above
and parallel to the compass needle direction - switch on and
then off - note what happens in each case.
_______________________________________________
_______________________________________________
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• Repeat step 4, except reverse the current direction - note
what happens this time.
_______________________________________________
_______________________________________________
• Observe the effect on the compass needle of increasing the
current in the wire.
_______________________________________________
_______________________________________________
• Hold the compass above the wire with the current on - note
what happens.
_______________________________________________
_______________________________________________
_______________________________________________
When there is no current in a wire there is no magnetic field.
However, when there is a current in a wire a ____________
________ surrounds the wire.
Reversing the current direction, _________ the direction of the
magnetic field.
Increasing the strength of the current __________ the
strength of the magnetic field.
A current carrying wire sets up its own _________ ______ and
the magnetic field is completely controlled by the ________.
The study of the relationship between electric current
current and
magnetic fields is called Electromagnetism.
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Experiment 4: Electromagnets
What you need: Length of wire (approx. 1 m), iron nail, paper
clip, low voltage power supply, safety glasses.
• Place the length of wire over the paper clip – does anything
happen?_________________________________________
_______________________________________________
• Wind half the length of wire round the iron nail and then
connect the ends of the wire to the power supply - switch
on the power supply at 2 V and hold over the paper clip –
note what happens.
_______________________________________________
_______________________________________________
• Increase the current through the coil (by increasing the
voltage to 4 V) – note any difference?
_______________________________________________
_______________________________________________
• Now return the voltage to 2 V and remove the iron nail
from the coil – note any difference?
_______________________________________________
_______________________________________________
• Repeat step 2, except wind all of the wire onto the nail,
noting any difference?
_______________________________________________
_______________________________________________
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• Now connect the ends of the wire to the a.c. terminals of
the power supply
upply and adjust to 2 V – note what happens?
_______________________________________________
_______________________________________________
When there is an __________ _________ in a wire which is
coiled round a piece a magnetic material e.g. ______, the
material becomes magnetised and
and an electromagnet is produced.
There is ____ magnetic effect when the current is switched off.
The electromagnet becomes stronger by:
(a) ____________ the current in the coil of wire;
(b) increasing the number of _______ in the coil of wire.
Without the iron core (iron nail) the electromagnet
electromagnet has
________ strength.
Iron is a magnetic permeable material which means that it
______________ the magnetic field within itself so giving a
____________ magnetic effect.
When an a.c.
.c. supply is used the electromagnet still works and as
the current alternates in direction so does the ___________
_________.
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Tutorial 2:
2 Magnetic Fields
The region of space surrounding a magnet where it produces a
magnetic force (effect) is called a magnetic field. It is useful
to think of a magnetic field as having a direction and to draw
lines (called lines of force) to show the magnetic field.
Magnetic field lines (or lines of force):
(a) Start on a N-pole
pole and end on a S-pole;
S
(b) Never touch or cross;
(c) Are closest together where the magnetic field is strongest.
(d) The arrows on the lines of force always point from North to
South.
A permanent magnet has a magnetic field surrounding it. A
magnet has two poles called north and south. Two like poles
repel, however two opposite poles attract. The magnetic field
can be represented by drawing field lines as shown. Lines that
physicsforums.com
used under Creative Commons License created by “geek3”
are close together indicate a strong field.
Permanent magnet field line pattern and electromagnet field line pattern
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Permanent magnets are not the only type of magnets. By passing
a current through an electrical conductor, a magnetic field can
be
e created around the conductor. This is known as an
electromagnet. Electromagnets are used in a variety of roles,
such as lifting cars at scrap yards, in electric bells and relay
switches.
The strength of an electromagnet depends on
• the number of turns of wire – more turns gives a stronger
electromagnet
• the size of the current through the wire – a larger current
gives a stronger electromagnet
• the presence of an iron core – an iron core electromagnet is
stronger than an air core electromagnet
Questions
1.
a) Two north poles are brought close together. Do they
attract each other or repel each other?
__________________________________________________
__________________________________________________
b) Two south poles are brought close together. Do they
attract each other or repel each other?
__________________________________________________
__________________________________________________
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c) A north pole and a south pole are brought close together. Do
they attract each other or repel each other?
__________________________________________________
2.
How is an electromagnet produced?
___________________________________________________
___________________________________________________
___________________________________________________
3.
What is the main advantage of an electromagnet over a
permanent magnet?
___________________________________________________
___________________________________________________
4.
Why are electromagnets used in scrap yards rather than
permanent magnets?
___________________________________________________
___________________________________________________
___________________________________________________
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Experiment 5: Electromagnets in Action
Electromagnets are essential parts of many electrical devices.
Your teacher will demonstrate a few of these devices.
Some of the more common devices are described below.
The Electric Bell
When the circuit is complete, the electromagnet becomes
magnetised and attracts the "soft" iron bar (or armature).
When the hammer hits the gong the circuit is broken at C.
Because the electromagnet has
now lost its magnetism, the
springy metal strip is now able
to pull the armature back, and
in remaking contact at C,
C
completes the circuit again.
Continuous ringing occurs as
long as the bell push is
depressed.
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Chimes
freely suspended
metal plate
When the bell push (switch) is pressed the coil becomes an
electromagnet. This pulls the soft iron collar fixed to the
bobbin. The bobbin moves to the right-hand metal plate and the
coiled spring is compressed. This produces the ‘ding’ sound. The
bobbin stays to the right for as long as a current is in the
electromagnet. When the switch is released, the electromagnet
is switched off allowing the coiled spring to push the rod back
striking the metal plate at Y to give a "dong".
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The Magnetic Relay
A magnetic relay is an electrically operated switch.
When 1st switch S is closed
2nd circuit
there is a small current in
the electromagnet. This
pulls the iron armature
towards the electromagnet
closing the contacts at the
2nd switch, and so there is a
current in the second circuit.
When S is opened the electromagnet loses its magnetism,
releasing the armature. The contacts at the 2nd switch open and
the current in the 2nd circuit stops.
Relays are used when it is desirable for a small current in the
control circuit to open or close a switch in a main circuit carrying
a large current.
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Unit 2: Section 2 - Additional notes
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Unit 2: Section 2 - Additional notes
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Unit 2: Section 2 - Additional notes
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Unit 2: Section 2 - Additional notes
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Unit 2: Section 2 - Additional notes
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Unit 2: Section 2 - Additional notes
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