GCSE Physics - The Oldershaw...
Transcript of GCSE Physics - The Oldershaw...
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LO – GCSE Physics Revision
GCSE PhysicsPaper 6
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LO – GCSE Physics Revision
Note to teachers
• This presentation contains revision material for all of the Paper 2 Physics examinations• Material that is only needed for Higher Tier pupils has titles highlighted in green (Sets 1 and 1.5)
• Material that is only needed for Separate Science pupils has titles highlighted in yellow
• Everything else is needed by everybody!
• Lots of the slides have automatic animation, wait for this to run through before clicking!
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LO – GCSE Physics Revision
SP8/CP7Energy – forces doing workThe one with lots of energy equations (easy marks!)
and the LAW OF CONSERVATION OF ENERGY.
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LO – GCSE Physics Revision
Brain empty
• Write down everything you know about energy changes in a mechanical system such as a roller coaster
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LO – GCSE Physics Revision
Energy is conserved
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LO – GCSE Physics Revision
Energy is conserved
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LO – GCSE Physics Revision
Energy is conserved
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LO – GCSE Physics Revision
Energy is conserved
4kg
5m
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LO – GCSE Physics Revision
Energy is conserved
5m
4kg 200 J
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LO – GCSE Physics Revision
Energy is conserved
5m
4kg 200 J200 = 1 4 x v2
2
xx
v2=100
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LO – GCSE Physics Revision
Describe and explain…
• Why does a roller coaster car always go slower at the end of the ride than your calculations predict?
• What happens to an electric motor that is overloaded and stops turning?
• How can mechanical energy losses be reduced?
• How can electrical energy losses be reduced?
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LO – GCSE Physics Revision
Describe and explain…
• Why does a roller coaster car always go slower at the end of the ride than your calculations predict?
• Energy is lost as heat and sound because of friction• What happens to an electric motor that is overloaded and stops turning?
• It overheats because no energy is transferred to kinetic, all is transferred to heat in the wires
• How can mechanical energy losses be reduced?• Use a lubricant to reduce friction• How can electrical energy losses be reduced?• Use smaller loads; smaller electrical current; lower resistance wire (super-cooled); to reduce heat losses
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LO – GCSE Physics Revision
Who is more powerful?
A man of mass 75kg runs up stairs 20m high in 10s
E = mghE = 75 x 10 x 20E = 15,000J
P = E/tP = 15,000 / 10P = 1500 Watts
A woman of mass 60kg runs up stairs 10m high in 4s
E = mghE = 60 x 10 x 10E = 6,000J
P = E/tP = 6,000 / 4P = 1500 Watts
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LO – GCSE Physics Revision
Calculate the work done lifting the boxes into the van.
150N
600N
3m
1.5m
E = F x dE = 600 x 1.5E = 900 J
The direction of the force and distance must be the same
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LO – GCSE Physics Revision
SP9/CP8Forces and their effectsThe one with force diagrams for everyone
with scale drawings for Higher students
and turning effects of forces for Separate Science students
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LO – GCSE Physics Revision
Brain empty
• Write down as many key words as you can remember that are linked to the idea of forces.
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LO – GCSE Physics Revision
Forces can be grouped into…
Can you list them?
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LO – GCSE Physics Revision
Forces are vectors and can be drawn as arrows…
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LO – GCSE Physics Revision
…and don’t forget:
Normal reaction forces are at 90o to the surface
Centripetal forces act towards the centre of the turn
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LO – GCSE Physics Revision
Or that:
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LO – GCSE Physics Revision
H Vectors can be added using scale diagrams
Scale 1cm : 10N
Use a pencil, ruler and protractor!
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LO – GCSE Physics Revision
H Vectors can be added using scale diagrams
What would the diagram look like if the object was in equilibrium?
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LO – GCSE Physics Revision
H Vectors can be added using scale diagrams
What would the diagram look like if the object was in equilibrium?
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LO – GCSE Physics Revision
S Turning effect of a force
The ”moment of a force” is the turning effect it has.
This is an anti-clockwise or negative moment.
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LO – GCSE Physics Revision
S Turning effect of a force
The ”moment of a force” is the turning effect it has.
This is a clockwise or positive moment.
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LO – GCSE Physics Revision
S Turning effect of a force
In equilibrium, the moments of all the forces add up to
zero.
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LO – GCSE Physics Revision
S Turning effect of a force
In equilibrium, the positive moments equal the negative moments in size.
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LO – GCSE Physics Revision
S What is the unknown force U?
fulcrum
Think…
Positive = Negativemoment moment
U x 1 = 400x0.25
U = 100 N
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LO – GCSE Physics Revision
S How does a lever help?
5m 1m
Anne is able to pull down on the lever with a maximum force of 700N. What is the maximum mass she is able to lift with the lever shown?
700 x 5 = F x 1
3500 = F
But F = m x g and g is 10N/kg on Earth,
so mass, m = 3500 / 10 = 350 kg
EXTENSION - If Anne used a lever made from a heavy material like steel, why would this
help her lift more mass?
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LO – GCSE Physics Revision
SP10/CP9Electricity and circuitsThe one that everyone needs to know everything for
and therefore guaranteed to come up
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LO – GCSE Physics Revision
Match the quantity with its symbol and unit
Symbol Quantity Unit
V electric current Joules (J)
I energy seconds (s)
P potential difference Coulombs (C)
E time Amperes (A)
t charge Watts (W)
Q power Volts (V)
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LO – GCSE Physics Revision
Match the quantity with its symbol and unit
Symbol Quantity Unit
V electric current Joules (J)
I energy seconds (s)
P potential difference Coulombs (C)
E time Amperes (A)
t charge Watts (W)
Q power Volts (V)
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LO – GCSE Physics Revision
Electric current
• Charge, Q, is counted in Coulombs (C)
• Current, I, is measured in Amperes (A)
• 1 Amp is 1 Coulomb of charge flowing past a point in 1 second
• You can work out the charge transferred in a time, t, measured in seconds (s)
Q
I
Remember this
formula
t
One electron is 1.6x10-19 C
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LO – GCSE Physics Revision
Simple electrical circuits
For electric charge to flow round a circuit, you need:• A complete circuit
• A cell to provide the “push” and the energy, called the emf (electromotive force) or voltage
• The current would be huge, going from + to –
• It would heat and melt the wires (a short circuit)
Secretly, it’s
electrons going the
other way!
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LO – GCSE Physics Revision
Simple electrical circuits
To stop the wires melting, we need:• A resistance• This “resists” the flow of current
• The current would decrease
• The energy is spent heating the resistor instead
Resistor, R
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LO – GCSE Physics Revision
Simple electrical circuits
The size of the resistance affects the current:
• A smaller resistance
• Allows more current flow
• A bigger resistance
• Allows less current flowResistor, R
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LO – GCSE Physics Revision
Simple electrical circuits
The size of the emf or voltage also affects the current:
• A bigger voltage
• Allows more current flow
• A smaller voltage
• Allows less current flowResistor, R
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LO – GCSE Physics Revision
Simple electrical circuits
• Voltage, V, is counted in Volts (V)
• Current, I, is measured in Amperes (A)
• You can work out the Resistance, R, measured in Ohms (Ω)
• 1 Ohm is when 1 Volt can push a current of 1 Amp
V
I
Remember this
formula
R
One Volt is 1 Joule of
energy per Coulomb, C
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LO – GCSE Physics Revision
Simple electrical circuits
Two components (parts) placed on the same line are said to be “in series”.
Resistor, R
A voltmeter can measure the potential energy difference between two points in the circuit:• This one measures the emf or
voltage supplied, 9V• This one measures the
potential difference of the resistor, 6V
• This one measures the potential difference of the bulb, 3V
9V
6V 3V
The voltages in the circuit add up to the total emf or
voltage supplied
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LO – GCSE Physics Revision
Simple electrical circuits
Resistor, R
If the resistance is decreased…• Less voltage is spent in the
resistor• More voltage is spent in the
bulb• The total resistance is less so
more current flowsIf the resistance is increased…• The opposite effect happens
9V
6V 3V
The voltages in the circuit add up to the total emf or
voltage supplied
3V 6V
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LO – GCSE Physics Revision
Simple electrical circuitsElectric current flow round a circuit is conserved:• what goes in must come out
When a new wire is added:• It gets its own current
• This adds to the current in the original circuit
Resistor, R
Resistor, R
This is a parallel circuit. The new wire makes it easier for current to get round, so the
total resistance is less
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LO – GCSE Physics Revision
Simple electrical circuitsCurrent can be measured using ammeters:• the current has to flow through the ammeter
• The current from the cell…
• …splits up through the two wires…
• …and rejoins to return to the cell
Resistor, R
Resistor, R
This is a parallel circuit. The new wire makes it easier for current to get round, so the
total resistance is less
4A
2A2A
2A2A
4A
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LO – GCSE Physics Revision
Resistance
Remember this?
Resistance is caused by:
• Collisions between electrons and atoms in the conductor
• Collisions between electrons when there are too many
Secretly, it’s
electrons going the
other way!
Resistance, R
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LO – GCSE Physics Revision
Resistance
Secretly, it’s
electrons going the
other way!
Resistance, R
6V
4A
We can measure:
• Current with an ammeter
• Voltage (pd) with a voltmeter
We can calculate:
• Resistance
• Power
• Energy usedfx sheet
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LO – GCSE Physics Revision
Resistance
Resistance, R
V
A
If we add a variable resistor:
• We can adjust the resistance
• Which changes the voltage on the resistance
• And changes the current that will pass through
Standard Test Circuit
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LO – GCSE Physics Revision
Resistance
Resistance, R
V
A
This allows us to plot a graph:
Standard Test Circuit
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0.25
-5 -4 -3 -2 -1 0 1 2 3 4 5
Cu
rren
t (A
)
Voltage (V)
V-I characteristics
Fixed resistanceEvery extra 1V gives an extra 0.04A of currentA bigger resistance
Every 1V only gives 0.02A of currentA smaller resistance
Every 1V gives 0.10A of current
Steep slope = small RShallow slope = big R
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LO – GCSE Physics Revision
Resistance
V
A
The graph for a bulb is:
Standard Test Circuit
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0.25
-5 -4 -3 -2 -1 0 1 2 3 4 5
Cu
rren
t (A
)
Voltage (V)
V-I characteristics
Steep = low R
Bulb heats up
Hot bulb = high RHigh R = shallow slope
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LO – GCSE Physics Revision
Resistance
V
A
The graph for a diode is:
Standard Test Circuit
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0.25
-5 -4 -3 -2 -1 0 1 2 3 4 5
Cu
rren
t (A
)
Voltage (V)
V-I characteristics
No current
Small V needed to make diode work
Steep slope = low RCurrent only flows
one way
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LO – GCSE Physics Revision
Resistance
LDR
V
A
An LDR acts like a normal resistor except:• When light hits it, R gets less
Standard Test Circuit
0
2
4
6
8
10
12
14
0 1 2 3 4 5 6
Res
ista
nce
Light intensity
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LO – GCSE Physics Revision
Resistance
V
A
A thermistor acts like a normal resistor except:• When it gets hot, R gets less
Standard Test Circuit
0
2
4
6
8
10
12
14
0 10 20 30 40 50 60
Res
ista
nce
Temperature
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LO – GCSE Physics Revision
SP11Static electricity and electric fieldSeparate science students only
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LO – GCSE Physics Revision
S How is static charge created?
• An atom is neutral, with equal + and – charges
• A material made from atoms is neutral too
• But if two different materials are rubbed together…
• Negative electrons can be transferred
+-
+
+-
+
+-
+-
+-
+-
-
-
Positive (loses e-)
Negative (gains e-)
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LO – GCSE Physics Revision
S Electrostatic force
Forces between charges
• + and + repel• + and – attract• – and – repel
The force is bigger if:• There are more – or more +
• The + and – are closer
Force on a neutral object
+
+
+
+
+
+
+
-
-
--
-
-
-
+-
Electrons move towards balloon, then
+ and - attract
Electrons move away from balloon, then
+ and - attract
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LO – GCSE Physics Revision
S Earthing and Cross-Bonding
To stop electric charge building up:
• Earth the object using a conductor
• Cross-bond all metallic parts
When you touch a charged object you act as an Earth wire and get a shock!
Gas Meter- - ----
Friction between gas and pipe
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LO – GCSE Physics Revision
S Describe and explain a situation when electric charge might be dangerous.
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LO – GCSE Physics Revision
S Describe and explain a situation when electric charge might be useful.
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LO – GCSE Physics Revision
S Electric fieldthe area around a charge where the force can be felt is the force field.
Around a positive charge Around a negative charge
Ask yourself:“which way will a positive proton move?”
STRONGIf lines are
close together
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LO – GCSE Physics Revision
S Electric field between particles
Attraction
or attracting
Repulsion
or repelling
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LO – GCSE Physics Revision
S Electric field between parallel plates
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LO – GCSE Physics Revision
SP12/CP10Magnets and magnetic materialsThe one about magnets and stuff.
There is a bit of Higher work about motors too.
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LO – GCSE Physics RevisionMatch up the key words and definitions
magnet
the area around a magnet where a
magnetic force can be felt
when an object has both North and South
poles
dipolar monopole non-magnetic
a single North or South pole
magnetica material that creates
a magnetic field
a material that can feel the effect of a
magnetic field
a material that can’t feel the effect of a
magnetic fieldmagnetic field
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LO – GCSE Physics RevisionMatch up the key words and definitions
magnet
the area around a magnet where a
magnetic force can be felt
when an object has both North and South
poles
dipolar monopole non-magnetic
a single North or South pole
magnetica material that creates
a magnetic field
a material that can feel the effect of a
magnetic field
a material that can’t feel the effect of a
magnetic fieldmagnetic field
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LO – GCSE Physics Revision
Use iron filings in a petri dish to show the magnetic field around a bar magnet:
Where is the magnetic field the strongest?
How do you know?
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LO – GCSE Physics Revision
How is a piece of magnetic material magnetized?
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LO – GCSE Physics Revision
How is a piece of magnetic material magnetized?
This is induced magnetism
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LO – GCSE Physics Revision
How is a piece of magnetic material magnetized?
It is lost if the magnet is removed or the metal is heated or hit with a hammer!
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LO – GCSE Physics Revision
What is the Earth’s magnetic field?
Where is the magnetic field the strongest?
How do we know there is a magnetic South Pole at what is called North Pole?
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LO – GCSE Physics Revision
14/06/2018 (c) RShoebridge2008 68
Remember electromagnetism?• When an electric current passes through a wire it creates a magnetic field
• This is called an induced magnetic field
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LO – GCSE Physics Revision
N
14/06/2018 (c) RShoebridge2008 69
Remember electromagnetism?
• If the wire is placed in an external magnetic field, the two magnetic fields have an effect on each other.
• What will happen?
• Wire gets pushed down
S
Field directions OPPOSITE so they ATTRACT
Field directions THE SAME so they REPEL
The Motor Effect
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LO – GCSE Physics Revision
H Fleming’s Left Hand Rule
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LO – GCSE Physics Revision
H How to calculate the force on a wire carrying current while its in a magnetic field• This is an equation on the paper:
F = B x I x L
Where:B = the magnetic field strength in TeslaI = the current in the wire in AmpsL = the length of the wire in metres
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LO – GCSE Physics Revision
SP13/CP11 Electromagnetic inductionThe one about generating electricity and transformers
mainly for Higher level students with some extra bits for Separatescience but be warned – some of it might come up on Foundation!
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LO – GCSE Physics Revision
The induction coil generatorA coil of wire is attached to an ammeter that measures electric current in Amps (A).
When a magnet is pushed into the coil the ammeter shows a current (anti-clockwise).
When the magnet is pulled out of the coil the ammeter shows a current (clockwise).
An electric current is a flow of electrons or charge.
This is called an Induction Coil.
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LO – GCSE Physics Revision
The induction coil generatorThe induced electric current changes direction if:• The magnet is pulled out• The other end of the magnet is pushed
in
The induced electric current is bigger if:• More coils are used• The magnet is stronger• The magnet is moved faster
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LO – GCSE Physics Revision
The generator (dynamo)
The generator spins a coil inside a magnet.
As the coil rotates past the magnet it induces an electric current that goes backwards and forwards in the wire.
This is alternating current.
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LO – GCSE Physics Revision
The generator (dynamo)
To increase the size of the alternating current:• Use more coils• Use a stronger magnet• Rotate the coil faster• Use a larger area coilPower stations use very large versions of dynamos that are attached to big fans called turbines.
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LO – GCSE Physics Revision
Alternating current
time
Cu
rre
nt
(A)
1/50th secondGenerators produce
alternating current which
changes direction in the
wire.
Mains electricity changes direction fifty times in one second.
This is 50Hz a.c.
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LO – GCSE Physics Revision
Heating effect of a current
• Power stations produce large currents that can heat up wires
• The power lost in a wire due to heating can be calculated using:• P ∝ I2 x R• Notice that if the current doubles, the power lost is 4x bigger!
• To stop this happening we need to use the lowest currents possible
• We use transformers to change the size of the current
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LO – GCSE Physics Revision
Safety with electricity
• compare the current into the circuit with the current out of the circuit
• if they are not equal it switches off
• protects against faults and electrocution
• Unplug everything, switch on RCD, plug back in one-by-one
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LO – GCSE Physics Revision
Safety with electricityFuse protects the cable from carrying too much current and catching fire.
A fuse will not protect you from electrocution UNLESS more than the correct amount of current flows through you!
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LO – GCSE Physics Revision
The step-up transformer
N
S
Take an iron core
Wrap a coil around it
Pass a current through the coil
A magnetic field is induced
Reverse the current
A magnetic field is induced
The magnetic field direction reverses
N
S
The electric current made in power stations is too big to send down cables, it heats them up and loses all its energy. To avoid this we use a step-up transformer…
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LO – GCSE Physics Revision
The step-up transformerThe electric current made in power stations is too big to send down cables, it heats them up and loses all its energy. To avoid this we use a step-up transformer…
Extend the core
Add a second coil
The induced magnetic field links both coils
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LO – GCSE Physics Revision
The step-up transformerThe electric current made in power stations is too big to send down cables, it heats them up and loses all its energy. To avoid this we use a step-up transformer…
More coils means more voltage
240V on 6 coils steps up to320V on 8 coils
1A on 6 coilssteps down to0.75A on 8 coils
The voltage increasesThe current decreases and this stops it heating the wire
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LO – GCSE Physics Revision
S Transformer calculations
The number of coils on the transformer effects the voltage.
6 coils 9 coils is x1.5So 240 Volts x1.5 360 Volts
But to conserve energy this means…3 Amps 1.5 2 Amps
This is so that V x I always gives thesame answer…240 x 3 = 720 = 360 x 2
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LO – GCSE Physics Revision
S Loudspeakers and microphonesMicrophoneAlternating current in coilinducesAlternating magnetic field in coilMotor effect causes coil to move past magnetPaper cone movesSound vibrations made
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LO – GCSE Physics Revision
S Loudspeakers and microphonesLoudspeakerSound vibrations madePaper cone movesDynamo effect caused by coil moving past magnetAlternating magnetic field in coilinducesAlternating current in coil
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LO – GCSE Physics Revision
SP14/CP12The particle theoryThe one about solids, liquids and gases
With some extra equations for the Separate scientists
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LO – GCSE Physics Revision
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LO – GCSE Physics Revision
Interconversions - the names for how they change state from to another
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LO – GCSE Physics Revision
Heating/Cooling Curves
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LO – GCSE Physics Revision
Heating/Cooling Curves
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LO – GCSE Physics Revision
Explain what the flat lines on the graph mean interms of energy and particles in matter
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LO – GCSE Physics Revision
Temperature is a measure of hot hotsomething is (oC)
Heat is a measure of the thermal energy contained in an object ( J )
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LO – GCSE Physics Revision
1kg of water 1kg of cooking oil
20°C50°C 80°C20°C
Identical rings turned on for 1 minute
The water heats up less than the oil.
The SAME AMOUNT OF HEAT produces HALF the TEMPERATURE RISE in the water as in the oil
30°
rise
60°
rise
….heating
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LO – GCSE Physics Revision
Specific heat capacity
The Specific Heat Capacity of an object, is the amount of
energy needed to change the temperature of 1 kg of
the substance by 1oC
Substance Specific heat capacity in J / kg °C
water 4181
oxygen 918
lead 128
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LO – GCSE Physics Revision
Calculating Specific heat capacity
ΔQ = m c Δθ
Q = energy transferred in Joules (J)
m = mass of substance in kg
c = specific heat capacity in J / kg/oC
θ = (theta) is the temperature change in degrees Celcius (oC)
How much energy must be transferred to raise the temperature of 2kg of water from 20oC to 30oC? [Specific heat capacity of water = 4200J/kg/oC]
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LO – GCSE Physics Revision
Specific Latent Heat
Changing from one state to another requires heat energy.
The heat energy is being used to change state, rather
than raise or lower the temperature of the substance.
The amount of energy required depends on the mass of
the substance and the material.
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LO – GCSE Physics Revision
Specific Latent Heat
The amount of energy required to change the state of 1kg of a substance at its melting point is called the specific latent heat of the substance
Q = m L
Q = the energy required to change the state
m = is the mass of the substance (kg)
L = the specific latent heat of the substance (obtained from the given data)
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LO – GCSE Physics Revision
Calculate the energy required to change a mass of 0.65kg of
ice at 0oC into water at 0oC where L = 3.34 X 105 J/kg
Q = m L
Q = (0.65kg) x (3.34 x 105 J/kg)
Q = 217100 J
Heat energy required to melt 0.65kg water is 217100J
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LO – GCSE Physics Revision
The Gas Laws
Three Laws that explain the relationship between:
Pressure & temperature of a gas – The Pressure Law
Volume & temperature of a gas – Charles’ Law
Pressure & volume of a gas – Boyle’s Law
Yes, everyone has to know this one!
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LO – GCSE Physics Revision
The Pressure Law
This is how the practical is done:
• The hot water bath heats the gas up.
• The thermometer measures the temperature of gas and water.
• The Bourdon gauge measures the pressure of the gas
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LO – GCSE Physics Revision
The Pressure Law
These are the results:
• At high temperature the pressure increases.
• At low temperature the pressure decreases.
Why?
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LO – GCSE Physics Revision
The Pressure Law
Because:
At high temperatures the gas particles move faster
They collide with the walls more often
They collide with the walls with more force
This increases the pressure.
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LO – GCSE Physics Revision
The Pressure Law
Because:
At low temperatures the gas particles move slower
They collide with the walls less often
They collide with the walls with less force
This decreases the pressure.
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LO – GCSE Physics Revision
The Pressure Law
Scientists drew a graph of their results…
They found that particles stopped moving at
-273.15oC
You can’t go colder than this because you can’t move any slower!!!
High pressureFast particles
Low pressureSlow particles
No pressureParticles at rest!
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LO – GCSE Physics Revision
The Pressure Law
WHAT A RUBBISH TEMPERATURE SCALE!!!They invented a new temperature scale so that:
• At zero the particles had no energy
• As it got hotter the particles moved faster
They called it the…
THERMODYNAMIC temperature scale (Kelvin)
Kelvin = Celsius + 273
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LO – GCSE Physics Revision
S Charles’ Law
If a gas is heated and is able to expand it will increase its volume
Why?
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LO – GCSE Physics Revision
S Charles’ LawIf a gas is heated and is able to expand it will increase its volume
Because:• The air on the outside is at a constant pressure
• The pressure inside the balloon is equal to this
• As the gas on the inside gets hot, the particles move faster, collide more often and with more force
• The pressure inside increases and this pushes the balloon outwards
• As the particles spread out, the pressure falls until it equals the outside pressure and the balloon stops expanding
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LO – GCSE Physics Revision
S Boyle’s Law
When you squash a gas into a smaller volume (very slowly) the pressure goes up
Why?
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LO – GCSE Physics Revision
S Boyle’s Law
When you squash a gas into a smaller volume (very slowly) the pressure goes up
Because:• The particles move closer together (more dense)
• They collide with each other more often
• They collide with the walls more often
• This increases the pressure
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LO – GCSE Physics Revision
S Boyle’s Law
There is a formula for Boyle’s Law:
p1V1 = p2V2
p1 is the start pressureV1 is the start volumep2 is the end pressureV2 is the end volume
NOTE: if you try to do Boyle’s Law experiments too fast, the gas heats up and loses energy to the surroundings
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LO – GCSE Physics Revision
SP15/CP13Properties of matter under stressThe one about stretching and squashing things
and for Separate students it also includes some stuff about liquid pressure (trying to squash water)
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LO – GCSE Physics Revision
Hooke’s LawHooke found that when you pull on a spring, the extension (extra length) gets bigger as the force gets bigger.
Force ∝ extension(proportional to)
F = k x X
F is the force you applyX is the extension
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LO – GCSE Physics Revision
Hooke’s LawHooke drew a graph to show his results
While it is straight, his Law works.
Once it starts to curve, the spring won’t go back to its normal shape so his Law is then broken
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LO – GCSE Physics Revision
Hooke’s LawHooke drew a graph to show his results
The gradient of the graph tells us what k, the spring constant is.
k = 4 / 0.4 = 10 N/m
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LO – GCSE Physics Revision
Hooke’s LawHooke drew a graph to show his results
The area under the graph tells us how much energy is stored in the spring
E = 4 x 0.4 = 0.8 J
2
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LO – GCSE Physics Revision
Remember…
Hooke’s Law applies just as well to things being compressed!
Compression = being squashed
Tension = being stretched
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LO – GCSE Physics Revision
S Pressure in liquids
Why?
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LO – GCSE Physics Revision
S Pressure with depth
As you go deeper under water, the weight of the water above presses down with more force. This increases the pressure.
Δp = 𝝆 d gΔp = change in pressure
𝝆 = density of liquid
d = depth
g = gravitational field strength
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LO – GCSE Physics Revision
S Which vase has the greatest pressure?
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LO – GCSE Physics Revision
S Pressure in all directions is equal in a liquid
The water sprays out of the bag in all directions at the same pressure.
Only a hole in the bottom of the bag would go faster.
Why?
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LO – GCSE Physics Revision
S Hydraulic lifts
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LO – GCSE Physics Revision
S Floating and sinkingForce downwards is the weight of the ball:F = m x gbut m can be worked out using the volume and density:
F = 𝝆ball x V x g
Force upwards is the weight of the water the ball has pushed out of the way:
F = 𝝆water x V x g