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Science
Junior Cert
Physics Revision Notes
By Peter Jackson
Junior Cert Science –Physics Notes
Peter Jackson
Author
These notes were brought to you by Peter Jackson. Peter is the Head of Science at St Columbas College,
Whitechurch, Co Dublin. Peter has over 30 years teaching experience and has corrected Biology papers for the
Department of Education for over 25 years and also marks appeals for the Department. Peter teaches Science at JC
and Biology and Chemistry at LC. Peter has also recently written a book for Leaving Certificate students 'Essentials
Unfolded - Chemistry ' specifically to help students studying Chemistry at LC. He has also given numerous courses on
Lab Safety and IT in Teaching.
We at mocks.ie are delighted to bring you these excellent notes at an affordable price.
© Mocks.ie 2011
Science – Physics Revision Notes Peter Jackson
Page 2
Junior Cert Science –Physics Notes
Contents
Physics ............................................................................................................................................................................... 5
Force and Energy .......................................................................................................................................................... 5
Measurement in Science............................................................................................................................................... 5
Density the mass per unit volume (kgm-3) .................................................................................................................... 6
Flotation for Solids and Liquids ..................................................................................................................................... 7
Force: ............................................................................................................................................................................ 7
Centre of Gravity ........................................................................................................................................................... 8
Equilibrium and the Law of the Lever ........................................................................................................................... 9
Pressure in Fluids (Liquids and Gases) ........................................................................................................................ 10
Atmospheric Pressure and its Relationship to Weather ............................................................................................. 11
Energy ......................................................................................................................................................................... 11
Energy Conversion ...................................................................................................................................................... 13
Work and Power ......................................................................................................................................................... 14
Heat, Light and Sound ................................................................................................................................................. 16
Heat ............................................................................................................................................................................. 16
The Difference Between Heat and Temperature.................................................................................................... 18
Heat Transfer .............................................................................................................................................................. 18
Light............................................................................................................................................................................. 20
Reflection and Refraction of Light .............................................................................................................................. 21
Sound .......................................................................................................................................................................... 23
Reflection of Sound ..................................................................................................................................................... 23
Hearing ........................................................................................................................................................................ 23
Magnetism, Electricity and Electronics ....................................................................................................................... 24
Magnetism .................................................................................................................................................................. 24
Static Electricity ........................................................................................................................................................... 25
© Mocks.ie 2011
Science – Physics Revision Notes Peter Jackson
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Junior Cert Science –Physics Notes
Current Electricity ....................................................................................................................................................... 26
Calculations based on Ohm’s Law ........................................................................................................................... 26
Electric Circuits ............................................................................................................................................................ 27
Electricity in the Home ................................................................................................................................................ 28
Electronics ................................................................................................................................................................... 29
Diode ....................................................................................................................................................................... 29
Light-emitting Diode (LED) ...................................................................................................................................... 30
Light-dependent Resistor (LDR) .............................................................................................................................. 30
© Mocks.ie 2011
Science – Physics Revision Notes Peter Jackson
Page 4
Junior Cert Science –Physics Notes
Physics
Force and Energy
Forces occur throughout nature and affect all aspects of living and working.
Energy cannot be created or destroyed. It is converted from one form to another.
It is in the process of these conversions that useful work is done.
Natural resources need to be conserved.
Measurement in Science
Temperature is the hotness or coldness of a body
Thermometer is used to measure temperature
o
o
Melting point of Ice (0 C)
Boiling Point of Pure Water (100 C)
Système International (SI) units
Scientists all over the world use these units for measurements to avoid confusion
Quantity
SI unit
Measuring Instrument
Length
m (metre)
Ruler, opisometer, callipers
Mass
kg (kilogram)
Torsion balance
Time
s (second)
Watch or timer
Derived Units are units which have to be workout out, using a formula, from the basic units listed above
Quantity
SI unit
Area
cm (square centimetre)
Volume
cm (cubic centimetre)
Density
gcm (grams per cubic centimetre)
Speed
ms (metres per second)
Velocity
ms in a named direction
Acceleration
ms (metres per second per second)
© Mocks.ie 2011
Formula
2
Area = length  width
3
Volume = length  width  Height
-3
Density = mass  volume
-1
Speed = distance  time
-1
Velocity = speed in a named direction
-2
Acceleration = change in velocity  time
Science – Physics Revision Notes Peter Jackson
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Junior Cert Science –Physics Notes
Calculations involving derived units are at the end of the chapter
Density the mass per unit volume (kgm-3)





3
More often given as grams per cm
Calculated by dividing mass by volume
You can be asked to find mass or volume of a substance if you are
given its density.
Use the triangle on the right to work out the formula
Cover the one you want to know and you are left with the formula
you need
o Mass = density  volume
o Volume = mass  density
o Density = mass  volume
Measure the Density of a Regular Solid



Measure the mass using a balance
Calculate: the volume using the appropriate formula
e.g. cube volume = length  width  height
Calculate: Density = mass  volume
Mass = 14.4 g
3
Volume = 2 x 2 x 4 = 16 cm
Density = M/V = 14.4/16
-3
0.9 g cm
Measure the Density of an Irregular Solid (stone)

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



Take a stone
Measure the mass using a balance (250 g)
Measure the volume of the stone by
displacement of water
3
Volume of water = 100 cm
3
Volume of water plus stone = 150 cm
3
Volume of stone = 150 -100 = 50 cm
Calculate the density
3
-3
Density = mass  volume = 250 g  50 cm = 5 gcm
Measure the Density of a Liquid (water)

Measure the volume of the water using a graduated cylinder
(remember have your eye level with the mark and measure from the bottom of the meniscus)
3
 Record the volume (200 cm )
 Place a beaker on the balance and zero it
 Carefully pour the liquid into the beaker
 Record the mass of the liquid (200g)
 Calculate the density of the liquid
-3
-3
 Density = mass  volume = 200g  200 cm = 1 gcm
-3
 The density of water is 1 gcm
Result: for Alcohol
3
 200 cm weighs 160 g
3
-3
 Density = 160g  200 cm = 0.8 gcm
Conclusion: Different liquids have different densities
© Mocks.ie 2011
Science – Physics Revision Notes Peter Jackson
Page 6
Junior Cert Science –Physics Notes
Flotation for Solids and Liquids
Relating Flotation to Density
-3
 Place different substances of know densities in water (1 gcm )
-3
and then in alcohol (0.8 gcm )
Results:
-3
 A table tennis ball (density 0.2 gcm ) will float on water and
on alcohol
-3
 A piece of wood (density 0.9 gcm ) will float on water but
sink in alcohol
-3
 A brass ball (density 8.4 gcm ) will sink in both
Conclusions
 A substance will
o float if it is less dense than the liquid
o sink if it is more dense than the liquid
Important for ships because fresh water is less dense than sea
water so a ship leaves the sea and goes into a river it will sink
deeper into the water.
The Plimsoll line, drawn on the ship’s side, gives the levels it will
sink to in different waters when fully loaded.
 Ice floats because it is less dense than water
Plimsoll Line
Liquids behave in a similar way provided they are immiscible (do not mix) see diagram on right.
Force:
something that can change the velocity of an object
A force can
 make it move or stop moving
 change its direction
 change its speed
 change its shape
Force is measured in Newtons (N)
Weight: the force that pulls a body towards the centre of the earth (due to gravity)
Weight = mass (kg)  10 N



A mass of 5 kg has a weight of 5  10 = 50 N
A mass of 20 kg has a weight of 20  10 = 200 N
The weight of a person on the moon would be approximately 1/6 of their weight on Earth because the moon
has 1/6 of the gravity of Earth but their mass would be the same in both places because the still contain the
same amount of matter.
Friction: the force that stops two surfaces moving while they are in contact
Is needed between
(a) your feet and the ground to allow you to move (you cannot move easily on ice)
(b) the brakes and wheels to stop a bicycle
Is not wanted
(a) in car engines - oil is put into the engine to reduce it by lubrication
(b) between a bicycle wheel and its axle – grease and ball bearings are used to reduce it by lubrication and
by reducing the surface area in contact.
© Mocks.ie 2011
Science – Physics Revision Notes Peter Jackson
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Junior Cert Science –Physics Notes
Friction and the Effect of Lubrication



Set up the apparatus as shown
Use two different surfaces e.g. polythene and sandpaper
Pull the block along each surface steadily and note the
reading on the Newton balance in each case
 Cover both surfaces with oil and repeat the procedure
Results
Surface
Without lubrication
With lubrication
Polythene
2N
1N
Sandpaper
7N
3N
Conclusion
 Rough surfaces cause more friction that smooth surfaces
 Adding a lubricant such as oil or water reduces friction
Tension: the force in an object (string) when it is pulled in opposite directions at the same time
The Relationship between the Extension of a Spring and the Applied Force
 Set up the apparatus as shown
 Measure the length of the spring with no weights in the pan
 Add a know weight to the pan and record the new length
 Work out the extension for the weight added
 Repeat for a series of known weights
 Divide the extension by the weight for each pair of readings
Result
 Dividing the extension by the weight added gives a constant value
Conclusion
 Hooke’s Law:
the extension of the spring is directly proportional to the weight on it
Centre of Gravity The point in a body where all its weight appears to act
Find the Centre of Gravity of a Piece of Card
 Set up the apparatus as shown
 Use a card with holes punched at several places around its edge
 Hang the card using a pin through one hole
 Hang a weight from the pin using a thread
 Draw a line to mark the position of the thread on the card
 Repeat for each hole
Result
 the card balances where the three lines meet
Conclusion the centre of gravity is where the three lines meet
Centre of Gravity and Stability
An object that stays steady is said to be in equilibrium (balanced)
It is stable if it returns to its original position after being tilted
It will return to its original position provided its centre of gravity remains within its
base
 A low centre of gravity makes an object more stable e.g. a racing car
 A high centre of gravity makes an object less stable
 A wide base increases stability
 A narrow base reduces stability
© Mocks.ie 2011
Science – Physics Revision Notes Peter Jackson
Page 8
Junior Cert Science –Physics Notes
Equilibrium and the Law of the Lever
Lever: a rigid body which can rotate about a fixed point called the fulcrum









The thing we want to move is called the load
The force we use to move it is called the effort
Fulcrum: the fixed turning point of a level
The force and the effort are usually on opposite sides of the fulcrum e.g. crowbar, scissors
Sometimes they are on the same side e.g. wheelbarrow, tweezers
Moment is the turning effect of a force
Moment = force  (perpendicular) distance between the force and the fulcrum
Clockwise moments work to turn the lever in the clockwise direction
Anti-clockwise moments work to turn the lever in the anti-clockwise direction
Law of the Lever: Sum of clockwise moments = Sum of anti-clockwise moments
Demonstrate the law of the Lever


Set up the apparatus as shown
Balance the metre stick at the 50 cm mark (use rubber
bands or sellotape)
 Hang two different weights on either side of the
fulcrum
 Move the weights until the metre stick is balanced again
 Record the weights and the distance of each from the
fulcrum
 Calculate the clockwise and anti-clockwise moments
 Repeat with different weights
Result: the clockwise moments = anti-clockwise moments when the system is in equilibrium
Everyday Applications of Levers
Crowbar, door handle, door, wheelbarrow, scissors, screwdriver
Learn two of the above examples
Calculations using the Law of the Lever
Calculate the value of force Z in the diagram above
Anti-clockwise moments = Clockwise moments
Force A x Distance A = Force C x Distance C
3 x 40 = Z x 20
3 x 40 = Z = 6 N
20
© Mocks.ie 2011
Calculate the distance R in the diagram above
Anti-clockwise moments = Clockwise moments
Force A x Distance A = Force C x Distance C
2 x 45 = 3 x R
2 x 45 = R = 30 cm
3
Science – Physics Revision Notes Peter Jackson
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Junior Cert Science –Physics Notes
Pressure: force per unit area





-2
(Nm )
Pressure is measured using a barometer or a Bourdon gauge
If the area is decreased the pressure is increased
Stiletto heels produce more pressure than normal heels
If the area is increased the pressure is decreased
Wide tyres produce less pressure on the ground than narrow tyres
Calculating Pressure
Calculate the pressure
exerted by a 24N weight on
2
an area of 6m
Pressure = Force  Area
-2
= 24  6 = 4Nm
If a 10N box exerts a pressure
-2
of 2 Nm on a floor calculate
the area of the box.
Area = Force  Pressure
2
= 10  2 = 5m
2
If a container with a base of area 2m
-2
exerts a pressure of 3 Nm on a floor
calculate the weight of the box.
Force = Pressure x Area
= 3 x 2 = 6N
Pressure in Fluids (Liquids and Gases)
Pressure increases with depth and density of the fluid
In fluids pressure acts equally in all directions
Show the Relationship between Pressure and Depth in a Liquid
 Set up the apparatus as shown
 Stopper the three spouts
 Fill the can with water
 Unplug the three spouts at the same time
 Note the distance the water shoots out from the can
Result: The deeper the water the further the water shoots out
Conclusion: pressure increases with depth
Air has Mass
 Weigh an empty balloon
 Fill it with air and reweigh it
 Calculate the change in mass
Result
 Change in mass = 3.04 – 3.00 = 0.04g
Conclusion: Air has mass
Air Occupies Space
 Take a test tube of air and place a piece of tissue paper in the bottom
 Turn it upside down and place it in a beaker of water
Result: the paper remains dry water does not enter the test tube
Conclusion: air occupies space
© Mocks.ie 2011
Science – Physics Revision Notes Peter Jackson
Page 10
Junior Cert Science –Physics Notes
Atmospheric Pressure and its Relationship to Weather
The atmosphere exerts pressure measured in hectopascals (hPa)
The greater the depth of the atmosphere the higher the pressure
Pressure decreases with increase in altitude (height above sea level)
Show that the Atmosphere Exerts Pressure
 Set up the apparatus as shown
 Place water in the bottom of an empty can
 Heat the water until it boils
 Replace the lid on the can
 Allow the sealed can to cool
Result: the can begins to crumple
Conclusion: the atmosphere exerts pressure
Atmospheric Pressure and Weather
Weather charts show variations in atmospheric pressure which are related to weather conditions
Isobars are lines which join points of equal pressure
Areas of high pressure are called anticyclones
 Air descends
 Air becomes drier so no clouds and no rain
 There is no wind so air is calm; shown by isobars far apart
 Winds blow in clockwise direction
Areas of low pressure are called depressions
 Air rises and cools as it rises;
 Water vapour condenses and forms clouds which cause rain.
 Winds blow into this area; shown by isobars close together
 Winds blow in anti-clockwise direction
Low pressure over Ireland - so air rising,
cools and forms clouds and rain
Isobars close together so windy
Everyday Applications of Pressure
 A pointed stake is easier to drive into the ground because the point gives greater pressure
 Thumb tacks are pointed to make them easier to push in
 Air pressure is used to measure altitude and predict weather
Energy
Energy is the ability to do work. It is measured in Joules (J)
Principal of Conservation of Energy
Energy can neither be created nor destroyed but can be changed from one form to another


When we do work we change energy from one form to another
When this happens some of the energy is always lost as heat (this is why perpetual motion machines are
impossible)
Forms of Energy
 Kinetic: (movement): a car has kinetic energy when it is moving
 Potential: (stored): a spring has potential energy when it is wound
 Heat: the sun produces heat energy which keeps us warm
© Mocks.ie 2011
Science – Physics Revision Notes Peter Jackson
Page 11
Junior Cert Science –Physics Notes
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
Electrical: can drive an electric motor
Magnetic: can be used to move things using an electric motor
Light: the sun produces light energy which can be used to make electricity and also food in plants
Sound: loudspeakers can make beads move by vibrations
Nuclear: Uranium has energy in its nucleus which can be used to produce heat in power stations
Chemical: is energy stored in chemicals such as food and fossil fuels e.g. oil and natural gas
Solar: is all the different forms of energy that are produced by the sun they include heat, light, and many
other forms of energy.
Renewable Energy: can be replaced naturally
 Wind: the movement of the air can be used to drive turbines
 Wave: the up and down movement of waves can be used to drive turbines
 Tidal: used to drive turbines as the sea moves towards and away from the shore
 Biomass: wood can be used to make heat by burning
Non-renewable Energy: cannot be replaced
Oil, coal, turf and natural gas are all fossil fuels that took millions of years to form so they cannot be replaced
The sun is our primary source of energy because it is used to make all our food
 Plants use it directly in photosynthesis to make food
 Animals use it indirectly by eating plants
 Fossil fuels were made from plants which used it to grow, and from animals that ate plants




Type
Advantage
Disadvantage
Solar
Will not run out, no carbon emissions
Does not work at night
Wind
Cheap, no carbon emissions
Only works when windy
Biomass
Plentiful, does not add to Greenhouse Effect
Expensive to run
Oil
Transport is designed to run on this
Limited supply so will run out, carbon
emissions
Nuclear
Gives large amounts of energy from a little
material
Radioactive waste is very dangerous
and long lasting, danger of devastating
explosion
Ireland is very dependent on fossil fuels for its energy needs at present
This is very expensive because we have to import most of it, and it will become more expensive as it
becomes scarcer
Adds to the greenhouse effect
We need to conserve energy
o by converting to more renewable energy sources such as wind and hydroelectric power to reduce
this dependency
o by using it more efficiently e.g. by increasing the insulation of our homes and workplaces
© Mocks.ie 2011
Science – Physics Revision Notes Peter Jackson
Page 12
Junior Cert Science –Physics Notes
Energy Conversion
Examples of Energy Conversions
Converter
From
To
Battery
Chemical
Electrical
Car engine
Chemical
Kinetic, heat, light and sound
Plants
Solar (light)
Chemical
Kettle
Electrical
Heat and sound
Microphone
Sound
Electrical
Chemical Energy to Electrical Energy to Heat Energy
 Set up the apparatus as shown
 Note the temperature of the bulb
 Close the switch to let the current flow for a few minutes
 Note the temperature of the bulb
Result: the temperature of the bulb rises
Conclusion: chemical energy (battery) drives electrical energy (a
current) through the bulb causing the release of heat energy which raises
the temperature.
Electrical Energy to Magnetic Energy to Kinetic Energy
 Set up the apparatus as shown
 Hold the nail above the paper clips
 Close the switch for a few seconds
Result: the paper clips jump up to the magnet
Conclusion: electrical energy (the current) causes the nail to attract the
paper clips(magnetic energy) which makes the paper clips jump up
(kinetic energy) to the nail
Light Energy to Electrical Energy to Kinetic Energy
 Set up the apparatus as shown
 Switch on a lamp and bring it close to the solar panel
Result: as the lamp approaches the panel the fan begins to turn
Conclusion: the solar panel turns light energy into electrical energy
which turns the fan (kinetic energy)
© Mocks.ie 2011
Science – Physics Revision Notes Peter Jackson
Page 13
Junior Cert Science –Physics Notes
Work and Power
Energy is the ability to do work and is measured in Joules
Work is done when a force moves a mass and is measured in joules (J)
Work = Force  Distance
Calculations
Calculate the work done when
an 12N force pushes a
shopping trolley 6m
Work = Force x Distance
= 12 x 6 = 72 J
The driver of a moving car applied the brakes. The brakes
produced an average stopping force of 8 kN (8000 N) and the car
stopped having travelled 20 m after the brakes were applied.
Calculate the work done in stopping the car.
Work = Force x Distance
= 8000 N x 20 m = 160,000 J (160kJ)
Power is the amount of work done per second and is measured in watts (W)
Calculations
Calculate the power needed to
push a 12N trolley 6m in 10
seconds
A girl of mass 60 kg (weight 600 N) climbed a 6 m high
stairs in 15 seconds. Calculate the work she did and the
average power she developed while climbing the stairs.
Work = 12N x 6m = 72J
Power = Work  Time
= 72J  10s = 7.2 W
Work = 600 N x 6m = 3600J
Power = Work  Time
= 36J  15s = 240 W
Calculations involving Derived Units
Area
A football field measures
100m long by 50m wide.
What is its area?
Area = length x width
= 100 x 50
2
= 5000 m
A sheet of paper is 30 cm long
2
and has an area of 4500 cm .
How wide is it?
Area = length x width
 Width = area  length
= 4500  30 = 15 cm
Speed
A train travels the 192 km
between Dublin and Limerick
in 3 hours.
What is its average speed?
Speed = distance  time
= 192  3
= 64 km/hr
A car travelled the 165 km between
Dublin and Belfast at an average
speed of 55 km/hr. How long did
the journey take?
Speed = distance  time
 time = distance  speed
= 165  55 = 3 hours
How far would a motor cyclist
go in 2.5 hours at an average
speed of 80 km/hr?
Speed = distance  time
 Distance = speed x time
= 80 x 2.5
= 220 km
Velocity
© Mocks.ie 2011
Science – Physics Revision Notes Peter Jackson
Page 14
Junior Cert Science –Physics Notes
A car moving north at a steady speed
travelled 100 m in 4 seconds.
What is its velocity?
Speed = distance  time
= 100  4
-1
= 25ms
-1
Velocity = 25ms North
(Velocity requires a direction)
Acceleration
A car accelerates from 0 to 96 km/hr in
six seconds.
What is its acceleration?
Acceleration = change in speed  time
= 98  6
-2
= 16 ms
A stone was dropped from the top of a tall cliff. The
stones approximate velocity was measured each
second as it fell. The data collected during this
experiment is given in the graph.
Use data from the graph to estimate the
acceleration of the stone as it fell.
Give the units of acceleration with your answer.
Pick any two times on the graph e.g. between 1
second and 3 seconds
-1
Change in velocity = 30 -10 = 20 ms
Time = 2 seconds
Acceleration = change in velocity  time
= 20  2
-2
= 10 ms
© Mocks.ie 2011
Science – Physics Revision Notes Peter Jackson
Page 15
Junior Cert Science –Physics Notes
Heat, Light and Sound
Heat, light and sound are forms of energy that have many applications in our lives.
Heat


Heat is a form of energy
When petrol burns in a car engine it causes the gases in the cylinders to expand pushing the pistons down.
Heat energy has been converted into kinetic energy (movement) which is used to propel the car forward
Heat causes solids, liquids and gases to expand by making the molecules vibrate more and move apart
Addition or removal of heat causes substances to change state
Sublimation: changing directly from a solid to a gas without becoming a liquid e.g. CO 2 and Iodine (I2)
Expansion of solids when heated and contraction when cooled
 Set up the apparatus as shown
 Make sure that the ball passes through the ring
 Heat the ball in a Bunsen flame
 Try to put the ball through the ring
Result: the ball does not pass through the ring
 Cool the ball under the cold tap
 Try to put the ball through the ring
Result: the ball passes through the ring
Conclusion: Solids expand when heated and contract when cooled
Expansion of liquids when heated and contraction when cooled
 Set up the apparatus as shown
 Make sure there is liquid in the glass tube
 Gently heat the bottom of the flask
Result: the liquid rises up the glass tube
 Allow the liquid to cool
Result: the liquid level in the tube falls
Conclusion: Liquids expand when heated and contract when cooled
Expansion of gases when heated and contraction when cooled
 Set up the apparatus as shown
 Heat the flask gently
Result: Air bubbles emerge from the flask
 Allow the flask to cool
Result: water enters and rises up the tube
Conclusion: gases expand when heated and contract when cooled
© Mocks.ie 2011
Science – Physics Revision Notes Peter Jackson
Page 16
Junior Cert Science –Physics Notes
Demonstrate the Expansion of Water on Freezing
 Fill a bottle with water
 Place in a freezer overnight
 Remove the bottle from the freezer
Result: The bottle has burst
Conclusion: Water expands when frozen
Consequences of the anomalous expansion of water







o
o
This property of water is very unusual in that it expands between 4 C and 0 C
It becomes less dense and so floats on water
This causes ice to form on top of lakes rather than at the bottom
The ice on top insulates the water below and stops the lake freezing to the bottom
This allows fish and other animals to stay alive
The expansion of water in pipes can cause the pipes to burst when frozen
The burst is not discovered until the ice melts
Determine the Melting Point of Ice
 Setup the apparatus as shown
o
 Use ice from the freezer (-5 C)
 Record the temperature every 30 seconds
 Stir the ice
Result: the temperature rises at first then stays
o
steady at 0 C while the ice melts
o
Conclusion: the melting point of ice is 0 C
Determine the Boiling Point of Water
 Setup the apparatus as shown
 Place the thermometer just above the water
 Heat the water
 Record the temperature every 30 seconds
Result: The temperature rises steadily then stays
o
steady at 100 C while the water boils
o
Conclusion: the boiling point of water is 100 C
Investigate the Effect of Pressure on the Boiling Point of Water
 Set up the apparatus as shown
 Make sure the clip is open and boil the water
 Note the temperature at which it boils
 Remove the heat source
 Close the clip
 Cool the flask with cold water to reduce the pressure in the flask
 Note the temperature
Result: the water boils at a lower temperature
Conclusion: reducing the pressure on the liquid reduces its boiling point
© Mocks.ie 2011
Science – Physics Revision Notes Peter Jackson
Page 17
Junior Cert Science –Physics Notes
The Difference Between Heat and Temperature





Heat is NOT the same as temperature
Temperature is the degree of hotness or coldness of a body. It is
measure using a thermometer
Heat depends on mass, temperature does not
An egg cup full of water and a bucket full of water can both be at the
o
same temperature (80 C)
The bucket will melt far more ice than the egg cup so it has far
more heat
Plot the Cooling curve of Stearic Acid
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Set up the apparatus as shown
Place a test tube of solid stearic acid into the beaker of hot water
When it has melted completely remove the test tube of molten
stearic acid and place it in a beaker of cold water.
Record the temperature of the stearic acid every 30 seconds
Plot the results as shown in the graph until it has all solidified
Result: The stearic acid cools and the temperature drops steadily
o
When it reaches 70 C the temperature remains steady while it is
solidifying, until all the acid has solidified
Conclusion: while the temperature is steady the liquid is
changing to a solid. The liquid is losing heat to the cold water.
The heat produced (or needed) to change state is called Latent
Heat
As it is melting the heat is being used to change the state
from solid to liquid
As it is cooling the heat is being given out to the cold water
The temperature remains steady at is its melting point
Heat Transfer
All hot bodies radiate heat
Transfer of Heat Energy by Conduction
 Set up the apparatus as shown
 Use rods that are the same thickness and length
 Pour boiling water into the tank
Result: The thumbtacks fell off at different times
 Copper fell first, the Brass, Aluminium and finally iron
Conclusion: solids conduct heat from particle to particle
 Different substances conduct at different rates copper
was best and iron worst
To show that Water is a Bad Conductor of Heat
 Set up the apparatus as shown
 Use a coin to hold the ice at the bottom of the tube
 Heat the water at the top of the tube
Result: The water boils at the top of the tube while the ice remains
at the bottom
Conclusion: water is a bad conductor of heat
© Mocks.ie 2011
Science – Physics Revision Notes Peter Jackson
Page 18
Junior Cert Science –Physics Notes
Transfer of Heat Energy by Convection


Set up the apparatus as shown
Place a crystal of potassium permanganate in the bottom of the beaker
using a glass tube
 Heat the beaker below the crystal
Result: the crystal dissolves and the pink colour is carried around the
beaker by convection.
 Hot water rises above the Bunsen and as it cools at the top it sinks
Conclusion: heat is carried through a liquid by movement of heated molecules.
 This is called a convection current
Transfer of Heat Energy by Radiation
 Set up the apparatus as shown
 Switch on the infra-red lamp
Result the temperature in the flask rises
Conclusion: heat travels to the flask by radiation
 Radiation does not need particles. It can travel through a
vacuum
 Heat from the sun reaches Earth through the vacuum of
space by radiation
Compare the Insulating Ability of Different Materials
 Set up the apparatus as shown
 Pour boiling water into both containers
 Record the temperature every two minutes for half an hour
 Repeat using different materials to insulate the container
Result: the temperature falls more slowly in the insulated
container
Conclusion: Insulating materials prevent heat passing through
 Different materials have different insulating abilities
 The slower the temperature drops the better the material is
at insulating
© Mocks.ie 2011
Science – Physics Revision Notes Peter Jackson
Page 19
Junior Cert Science –Physics Notes
Light
Light is a form of energy and that it can be converted to other forms of energy
 Plants use photosynthesis to change light energy to chemical energy
 Solar cells convert light energy to electrical energy which can then be used to drive a fan (kinetic
energy)
Objects that produce light are said to be luminous
Luminous objects include: the sun, light bulbs, fire
Objects that do not produce light are non-luminous are seen as a result of light reflected from them
Speed of Light: 300 million metres per second
Show that Light Travels in Straight Lines
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Set up the apparatus as shown
Line up the three holes using a metal rod
Light the candle and look through
Result: you see the candle
Move one of the cards
Result: you do not see the candle
Conclusion: Light travels in straight lines
How Shadows are Formed
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Set up the apparatus as shown
Use a small bright light source
Place the key between the light source and the screen
Result: a shadow forms on the screen
The shadow has the same shape as the key
Conclusion: A shadow results from light travelling in straight
lines being blocked by an opaque object such as a key
Producing a Spectrum
 Set up the apparatus as shown in the diagram
 Use a ray box to produce the beam of white light
 Shine the ray of white light through a prism
 Result: a spectrum forms on the screen
 Conclusions:
 The white light is dispersed (spread out) by the prism
 White light consists of red, orange, yellow, green, blue,
indigo and violet light
 Red is bent least and violet is bent most
 This group of colours is called the spectrum
© Mocks.ie 2011
Science – Physics Revision Notes Peter Jackson
Page 20
Junior Cert Science –Physics Notes
Reflection and Refraction of Light
Reflection of Light by a Plane Mirror and use of Ray Diagram
 Place a plane mirror on a sheet of paper
 Draw a line (N) perpendicular to the mirror
 Shine a ray of light to the point where this line meets the mirror
 Mark the position of the ray of light using four dots as shown
 Draw the rays using a ruler
 Measure the angles A and B
Result: angles A and B are the same
Conclusion: the reflected ray bounces off the mirror at the
same angle as the original ray
 The image in a mirror is reversed
 Ambulance is written in reverse on the front so it appears the right way round in car mirrors
Demonstrate the Operation of a Simple Periscope
 Set up the apparatus as shown
o
 The two lenses are set at 45 in the tube
o
 The first mirror bends the light 90
o
 The second mirror bend the light 90 in the opposite direction
Result: the path of the light has been moved by the distance
between the two mirrors
Conclusion: a periscope can be used to see around corners or
over the heads of people
 The image in a periscope is the right way round due to double reflection
Refraction of Light from Air to Glass and Glass to Air

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Set up the apparatus as shown in the diagram
Draw the outline of the glass block with a pencil
Shine a ray of light at the glass block at an angle
Mark the position of the ray into the glass with two dots as
shown
 Mark the position of the ray out of the glass with two dots
as shown
 Remove the block of glass
 Draw the two rays and then join them
Result: the ray bends one way as it enters from air to glass
 The ray bends the other way as is goes from glass to air
Conclusion: Light refracts in opposite directions as it goes
from glass to air and from air to glass
 The ray coming out is parallel to the ray entering
© Mocks.ie 2011
Science – Physics Revision Notes Peter Jackson
Page 21
Junior Cert Science –Physics Notes
The Refraction of Light from Air to Water and Water to Air
Water to Air
 Place a coin in an empty basin
 Adjust your position till the coin is just hidden
 Get a friend to fill the basin with water
Result: The coin becomes visible as the basin is filled
Conclusion: Light is bent as it goes from water to air
Air to Water
 Fill a beaker with water plus a little dye
 View it from the side
 Darken the room
 Shine a ray of light into the water
Result: the ray of light can be seen bending as it enters the water
Conclusion: Light is bent as it passes from air to water
Show Refraction of Light through a Lens;
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When light passes through a lens it is refracted (bent)
A convex lens brings the rays together at one point (the focus)
A concave lens spreads the rays apart
Demonstrate the Operation of a Magnifying Glass
 Take a sample of print
 Place a magnifying glass over the print
Result: The print appears bigger
Conclusion: a magnifying glass makes things appear bigger
Applications
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Reflection: mirrors
Refraction: to focus images using lenses in microscopes, spectacles and telescopes
© Mocks.ie 2011
Science – Physics Revision Notes Peter Jackson
Page 22
Junior Cert Science –Physics Notes
Sound
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Sound is a form of energy
It is produced by vibrations (of your vocal cords or a loudspeaker)
To Show that Sound is a Form of Energy

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Set up the apparatus as shown
Switch on the signal generator
Result: the polystyrene ball moves when the sound is turned on
Conclusion: Sound is a form of energy and is changed into
kinetic energy when the ball moves
Show that Sound Transmission Requires a Medium
 Set up the apparatus as shown
 Switch on the bell
 Turn on the vacuum pump
Result: as the air is removed the sound gets weaker
Conclusion: sound needs a medium to travel
 Ultrasound uses echoes to study babies in the womb without harming
them
 Sonar uses echoes to measure the depth of water or locate
submarines
The time lag between seeing and hearing the same event

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As lightning jumps from a cloud to earth thunder is formed
-1
The speed of light (300,000,000 ms ) is so big that the flash
reaches the viewer almost instantaneously
-1
Sound is much slower (340 ms )so it takes a measurable
time to reach the viewer (about 4 seconds for every 1500 m)
Reflection of Sound
Show that Echoes are Reflected Sound
 Find a large open space with a high wall
 Clap your hands once, loudly
Result: after a short delay the sound is heard a second
time
Conclusion: the second sound is caused by the sound
reflecting off the wall and returning to you
 This is called an echo
Hearing
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The inner ear detects sound
Sound is measured in decibels
Very loud sounds can damage your ears
o Don’t play music too loudly.
o The ringing in your ears after a rock concert is a sign of damage
Continuous loud noise can also damage your ears so if you are operating a machine wear ear protectors
© Mocks.ie 2011
Science – Physics Revision Notes Peter Jackson
Page 23
Junior Cert Science –Physics Notes
Magnetism, Electricity and Electronics
Magnetism is a natural phenomenon with many useful applications.
Electricity is a form of energy. Electricity makes a significant contribution to all aspects of our lives.
Magnetism
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A magnet is a substance that has the ability to attract other metals to it
Iron and Nickel and some of their alloys are the main magnetic substances
Magnets have two centres of attraction called poles
The end of a freely moving magnet that points north is called the North Pole
The end of a freely moving magnet that points south is called the South Pole
Magnetic Field: is the area around a magnet where the magnetic force acts
The Earth’s Magnetic Field
 The earth is a giant magnet
 This allows us to navigate using a compass
 It protects us from solar winds of charged particles
The Magnetic Compass
 This is a magnet that is free to rotate horizontally
 It can be used to tell the direction you are travelling
Magnetic Compass
Earth’s Magnetic Field
Demonstrate that the Earth has a Magnetic Field, and Locate North and South
 Suspend a magnet as shown
Result: the magnet always comes to rest in the same position
Conclusion: the Earth has a magnetic field
 The end pointing north is the North Pole
 The end pointing south is the South Pole
Show Attraction and Repulsion between Magnets
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Set up the apparatus as shown
Bring the opposite poles of the two magnets close
to each other
Result: they move together
 Bring the similar poles of the two magnets together
Result: they move apart
Conclusion: unlike poles attract, like poles repel
Test Materials for Magnetism
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Place the substance to be tested on the bench
Bring magnet near the substance
If the substance sticks to the magnet then it is magnetic
If the substance does not stick to the magnet then it is not magnetic
Plot the Magnetic Field of a Bar Magnet
 Draw the outline of a bar magnet on a sheet of paper
 Place a plotting compass at one end of the magnet
 Mark the position of the pointer tip with a dot
 Move the compass so that the tail of the pointer is at the dot
 Mark the tip of the pointer
 Continue doing this until you reach the opposite pole of the magnet
 Join the dots with a line
 Repeat several times starting at different points
Result: you have plotted the magnetic field of the magnet
© Mocks.ie 2011
Science – Physics Revision Notes Peter Jackson
Page 24
Junior Cert Science –Physics Notes
Static Electricity
Current Electricity occurs when a body has charges running through it
Static Electricity
 Occurs when a body has charges that are fixed and cannot move
 Caused when two insulating materials are rubbed together
Electric Charges
 Positive
o Caused by removal of electrons form a substance
o Rub a Perspex rod with a dry woollen cloth
 Negative
o Caused by the addition of electrons to a substance
o Rub a polythene rod with a dry woollen cloth
Use Simple Materials to Generate Static Electricity
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Take a comb and comb it through dry hair
Take a Bic biro and rub it on a woolen jumper
Hold both near some scraps of paper
Result: the paper is attracted to the comb and biro
 Both have become charged by rubbing
 Touch the end of each with a wire connected to earth
Result: The paper falls off
Conclusion: Earthing a charge body removes its charge
Demonstrate the force between charged objects
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Charge a polythene rod, suspend by a thread, by rubbing
Charge another polythene rod by rubbing and bring it
close to the suspended rod
Result: The suspended rod is repelled
Conclusion: Like charges repel
 Charge a perspex rod by rubbing
 Bring it close to a suspended charged polythene rod
Result: The polythene rod is attracted to the perspex rod
Conclusion: Unlike charges attract
Test Electrical Conduction in a Variety of Materials
 Set up the apparatus as shown
 Place the material being tested between the two clips
 Close the switch
Result: If the bulb lights then the substance is a conductor
 If the bulb does not light then the substance is an insulator
© Mocks.ie 2011
Science – Physics Revision Notes Peter Jackson
Page 25
Junior Cert Science –Physics Notes
Current Electricity
Description
Units
Symbol
Instrument
Current
A flow of charge
Amps (A)
I
Ammeter
Voltage
Difference in electric potential between two points
Volts (V)
V
Voltmeter
Resistance
Ability of a substance to reduce current
Ohms ()
R
Ohmmeter
To Determine the Relationship between Current, Potential Difference (Voltage) and Resistance
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Connect the circuit as shown in the diagram
Set the voltage to 1 volt
Read the current flowing on the ammeter
Increase the voltage to 2 volts
Read the current flowing on the ammeter
Continue in this way till 10 volts
Divide the voltage by the current in each case
Result: voltage divided by current is a constant
Conclusion: voltage divided by current is a constant called the
resistance
Note: If the current and voltage are plotted a straight line graph going
through the origin results, showing that current is proportional to
voltage.
 This is called Ohm’s Law
Calculations based on Ohm’s Law
What is the resistance of a 6
volt torch bulb that takes a
current of 2 Amps?
What current flows through an
8 ohm resistor if it is connected
to a 12 volt battery?
A heater has a resistance of 60 ohms
and takes a current of 4 amps, what is
the voltage of the electricity supply?
R=V/I=6/2=3
I = V / R = 12 / 8 = 1.5 A
V = I x R = 4 x 60 = 240V
Direct Current (DC) current flows in one direction round a circuit (from positive to negative)
Alternating Current (AC): Current changes direction every one hundredth of a second
© Mocks.ie 2011
Science – Physics Revision Notes Peter Jackson
Page 26
Junior Cert Science –Physics Notes
Heating Effect of an Electric Current
 Set up the apparatus as shown
 Place the thermometer next to the bulb
 Close the switch to light the bulb
Result: the temperature of the bulb increases
Conclusion: the electric current has a heating effect
Chemical Effect of an Electric Current
 Set up the apparatus as shown
 Make sure the test tubes are filled with water
 Switch on the current
Result: Two gases are produced Hydrogen at the negative electrode
and Oxygen at the positive electrode
Conclusion: The electric current has caused a chemical reaction
to take place
 This is called electrolysis
Magnetic Effect of an Electric Current
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Set up the apparatus as shown in the diagram
Make sure the compass needle is pointing in the same
direction as the wire
Close the switch for a second
Result: the compass needle turns
Conclusion: the electric current has a magnetic effect
Effect
Everyday Applications
Heating
Kettles and boilers to heat water, electric fires and fuses
Chemical
Making hydrogen and electroplating car bumpers with chromium
Magnetic
Used in scrapyards to lift iron (steel) objects and also in electric motors
Electric Circuits
Simple Series and Parallel Circuits containing a Switch and Two Bulbs
1. Series
 The current has to pass through one bulb to get to the
next bulb i.e. they are in sequence
 Both bulbs shine with equal brightness
 These bulbs do not light as brightly as they would if
connected in parallel
 If one bulb blows then the current will not flow so the
other bulb will go out e .g. cheap fairy lights
2.
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Parallel
The two bulbs are arranged in parallel
Both bulbs shine with equal brightness
These bulbs light more brightly than they would if
connected in series
© Mocks.ie 2011
Science – Physics Revision Notes Peter Jackson
Page 27
Junior Cert Science –Physics Notes

If one bulb blows then the current will continue to flow through the other one, so it will not go out
e.g. expensive fairy lights
Function of a Switch
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A switch is a device which makes or breaks a
circuit
When the switch is closed the circuit is complete and
current will flow
When the switch is open the circuit is broken and the
current will NOT flow
Electricity in the Home
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Mains Supply is the electricity supplied from the National Grid
This is alternating current (a.c.) at 230 V
Electricity supply companies charge customers for each kilowatt hour (unit) they use.
A kilowatt hour is the amount of electricity a 1 kilowatt appliance (a 1 bar electric fire) would use if
kept running for one hour
The cost of a unit varies from company to company
Units used at night are cheaper than those used during the day
Calculate the cost of heating a room for 12 hours
using a 3000 watt heater if 1 unit costs 15 cents.
Units = kilowatts x hours
3000 W = 3 kW
Units = 3 x 12 = 36
Cost = 36 x 15 = 540 cent = € 5.40
Wiring a Plug
Make certain that
 Each colour coded wire is connected to the correct terminal
o Brown  Live terminal
o Blue  Neutral terminal
o Green/yellow  Earth terminal
 The screws are fully tightened
 No bare wires are exposed
 The fuse is of the correct rating
 The cord grip is holding the outer covering of the cable
Power Rating of Electric Appliances
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On the label of all electrical appliances you will find their power rating
-1
This is how much power it uses in Watts (Js )
The more powerful an appliance is the more electricity it will use and the more expensive it will be to operate
o Video Recorder – 50 W
o Kettle – 1.5 kW (1500 W)
o Cooker – 11 kW (11000 W)
Safety
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Fuses stop too much current flowing through a circuit
The greater the current that flows the more heat that is produced in the fuse wire
© Mocks.ie 2011
Science – Physics Revision Notes Peter Jackson
Page 28
Junior Cert Science –Physics Notes
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If too much current flows it becomes so hot that it melts thus breaking the circuit and cutting off the
supply of electricity to the device
Circuit breakers do the same job but work using electromagnetism
It is important to use the correct fuse value. Some examples are given below
o Television – 5A
: Hoover – 13 A :Cooker – 25 A
Electronics

Electronic Devices are used to control very small currents in computers, televisions, mobile phones, etc
Electronic Device Symbols
Device
Appearance
Symbol
Device
Battery
Buzzer
Bulb
Switch
Diode
Light
Emitting
Diode
Resistor
Light
Dependent
Resistor
Appearance
Symbol
Diode is a device that allows current to flow in one direction only
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Current (flowing from + to -) can pass through in the direction of the arrow
If current can pass through it is said to be forward biased
If current cannot pass through it is said to be reverse biased
Current cannot pass through - reverse biased
Current can pass through - forward biased

© Mocks.ie 2011
In A and B above: when the battery is reversed then the
direction of current is reversed and the current can flow
through the other diode and buzzer.
 In C, to the left, the LED has a small resistance so too
much current might flow and burn out the diode: the
resistor is added to reduce the current flowing and so
Science – Physics Revision Notes
Peter this
Jackson
Page 29
prevent
happening
Junior Cert Science –Physics Notes
Everyday Applications
 Rectifying AC (turning AC into DC)
 Protect circuits for reverse battery connection
Light-emitting Diode (LED) a diode that gives out light when a current flows through it
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Requires less current than a bulb
Used in the latest television screens, as lights to warn that a device is on, or in stand-by mode
Used to make numbers on electronic gauges
Last longer than bulbs
Less prone to damage than bulbs
Light-dependent Resistor (LDR) is a resistor whose resistance decreases with increasing light intensity
Measure the Resistance of a Light-dependent Resistor (LDR)

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Set up the apparatus as shown
Measure the resistance with the lamp off
Switch the lamp on and measure the resistance
Move the lamp closer and measure the resistance
Result: the brighter the light falling on the resistor the
less the resistance
Conclusion: the resistance of LDRs decreases with light intensity
Everyday Applications
 Light meters
 Automatic light switches in street lamps
© Mocks.ie 2011
Science – Physics Revision Notes Peter Jackson
Page 30