Download chemistry class notes

D. Mac an Aircinn 
J.C.E. Eolaíocht
Important
These notes are not a substitution for your textbook. They are meant to facilitate quick revision and when you are
answering questions you may need to include more detail. Remember when describing experiments you must
always include a diagram. Note not all the experiments in these notes have diagrams included, but you should be
able to draw suitable diagrams for them yourself after reading the method. If you cannot, go back to your
textbook and learn an appropriate diagram for the experiment.
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Eolaíocht J.C.E.
D.Mac an Aircinn
Introduction
How Scientists Work
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Study the world around them and ask questions.
They to explain what happens in the world by making a theory.
They test their theories by doing experiments.
The results tell them if their ideas are right or if they need to change them.
This way in which scientists work is often called scientific method.
Planning an Experiment
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What are you trying to find out?
How will you make the experiment a fair test?
What materials and equipment do you need to carry out the experiment?
What measurements will you need to make?
What results to you expect to get?
In what ways must you be careful to avoid errors?
Writing an experiment report
The following should be included in every experiment report.
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Date
Names of the group members.
Title or Aim (say what you are trying to find out or prove)
Method or Procedure (explain how the experiment should be done)
List of apparatus (say what equipment and materials are needed)
Diagram (a drawing to show the equipment is arranged)
Results or Observations (say what you seen happen or record your measurements in a
table)
Calculations (if needed, show how the calculations are done)
Graph (if needed, draw a graph of the results)
Conclusion ( say if you proved what you set out to prove or what went wrong)
You should always look at the experiment to see what the possible errors are.
Physics is the science of measurement involving electricity, magnetism, light, heat, sound and electronics.
Chemistry is the study of the chemical properties of substances. and changing one substance to another.
Biology involves the study of animal and plant life.
The following is a list of common laboratory equipment you should be familiar with and be able to draw .
Beaker, test tube, tripod, pipe-clay triangle, wire gauze, conical flask, funnel, retort stand, graduated cylinder,
crucible , test tube holder, evaporating, petri dish, deflagrating spoon, spatula, clock glass, test tube rack and
bunsen burner.
Introducing Physics
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Measurement
Length is measured with a metre stick or ruler. Outside and inside diameters are measured using a
callipers or vernier callipers. Curved lines are measured using a opisometer. The units of length are metres. Area
is the amount of surface covered. measured in cm2 or m2. For regular objects area = length x breath. Volume is
the amount of space something takes up. Volume = length x width x height, units cm3 or m3.
Exp.To find the volume of a stone
Water
Stone
Graduated
cylinder
Displacement
Can
1.
2.
3.
Fill a displacement can to the spout with water.
Put a clean dry graduated cylinder below the spout and lower the stone in carefully.
Record the amount of water collected, this is the volume of the stone.
Density
Mass is a measure of difficult it is to change the velocity of a body. (kg) Density is the mass of a unit volume of
a substance (g/cm3).
Exp.To find the density of a substance (stone)
1. Fill a displacement can to the spout with water.
2. Put a graduated cylinder below the spout and lower the stone in carefully.
3. The amount of water collected is the volume of the stone.
4. Find the mass of the stone on a balance.
5. Divide the mass by the volume to get the density
Floatation
If an object floats in water then it's density is less than the density of water. In any object floats it is less dense
than the fluid it floats in and vice versa.
Motion Force Levers and Pressure
Distance
Speed =
time
(m/s)
Displacement is the distance travelled in a particular direction (m).
Momentum= Mass x Velocity (kgm/s)
Velocity =
Distance in a given direction
Time
Acceleration =
Change in Velocity
Time
(m/s)
(m/s )
2
Honours students should be able to draw graphs of velocity and acceleration and answer questions on them.
You must be able to draw graphs of distance against time and velocity against time and interpret the graphs.
Force
A force is anything which changes the velocity of an object. (N). Forces cause movement, bending, squeezing,
twisting and stretching. Forces always occur in pairs. Weight is the force due to gravity.
Weight = Mass x 10 measured in newtons
Friction is the force due to two or more surfaces rubbing off each other. Friction can be a nuisance by slowing
things down, wearing away surfaces in contact and producing heat. Friction can be useful such as for brakes on a
car, allowing you walk or run. Friction can be reduced by using oil, ball bearings, polishing surfaces or
streamlining objects like racing cars. The mass of a body is the same wherever you are but weight depends on
your distance from Earth.
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Stretching forces cause objects to change shape, in this case get longer. This happens with springs.
When the force is removed the spring returns to its original shape. Substances that do this are said to be elastic.
We can use the extension of springs as a way of measuring mass or weight.
Hooke’s Law states that the extension of a spring is directly proportional to the force stretching it.
Levers
Title To verify Hooke’s Law.
Diagram
Method
1.
2.
3.
4.
5.
Set up the apparatus as shown in the diagram.
Record the reading on the ruler, this is zero extension.
Add a weight to the pan and record the new reading.
Repeat 3 until you have 6 – 10 results.
Plot a graph of force (weight) against extension.
spring
Results
Reading (cm)
Ruler
Force (N)
Extension (cm)
Pan for
weights
Work
Power =
Time
(W)
Retort stand
Work is done when a force moves an object. Work = force x distance. (J).
Power is the work done per unit time. (W)
A lever is a rigid body which is free to move about a fixed point called the fulcrum.
The Centre of Gravity of gravity of a body is the point through which the weight acts no matter what position
the body is in. There are three states of equilibrium , stable equilibrium, unstable equilibrium and neutral
equilibrium. A body is in stable equilibrium if moving it raises its centre of gravity, e.g. a bottle the right way
up. A body is in unstable equilibrium if moving it lowers its centre of gravity, e.g. a bottle upside down.
A body is in neutral equilibrium if, when moved it centre of gravity neither falls or rises.
The lower the centre of gravity and the wider the base of the object the more stable it is, i.e. the less likely it will
topple over. This is why racing cars are low to the ground and the cars are wide.
The law of the lever states that when a lever is balanced the sum of the clockwise moments = the sum of the
anticlockwise moments.
Exp. To Prove the law of the lever
1. Balance a metre stick on a pencil.
2. Put a known weight on one side and a known weight on the other side.
3. Adjust the positions of the weights until the metre stick is balanced..
4. Measure the distance from the fulcrum for both weights
5. Calculate the clockwise and anti clockwise moments.
6. You should find that they are equal thus proving the law of the lever.
Pressure is a force which depends on area, small area = high pressure.
Force
Pressure in liquids depends on depth and density.
Pressure =
(N)
The force of gravity on the atmosphere causes atmospheric pressure.
Area
Pressure
Exp. To demonstrate atmospheric pressure.
1. Heat a small amount of water in an old oil can
2. Let the water boil and the steam drive all the air out
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3. Remove the heat and seal the can tightly.
4. As the can cools the sides collapse inwards
5. This shows the atmosphere exerts pressure
The greater the height above the Earth the lower the atmospheric pressure. Atmospheric pressure is measured
using a mercury or aneroid barometer.
A mercury barometer is made by filling a stout walled glass tube 1 m long with mercury. The tube is then
inverted into dish of mercury and the level falls to about 76cm, normal atmospheric pressure. The vacuum at the
top is called a torricellian vacuum.
Atmospheric pressure is used to predict weather, e.g. high pressure usually good sunny days in summer.
An aneroid barometer can be converted to measure height, called an altimeter. The corrugated box with a partial
vacuum expands and contracts due to pressure and this moves the needle to give the pressure.
Pressure in liquids depends on depth. The greater the depth the greater the pressure. This is why dams are built
much wider at the bottom than at the top.
Some uses of pressure
 Hydraulic fluid in the braking systems of cars, pressing the break pedal puts pressure on the break fluid
and pushes the break pads onto the wheel to stop the car.
 Reservoirs of water have to be higher than the taps they supply in order for the water to flow when the
tap is switched on.
 The difference in pressure above and below the wings of an aeroplane allow it to fly.
 Pumps for beer, water, create a difference in atmospheric pressure to draw up the water or beer.
Heat and Energy
Energy is the ability to do work. Conservation of Energy means energy cannot be created or destroyed. There
are many forms of energy including kinetic, potential, Radiant(light), internal(heat), electrical, sound and nuclear
energy. Oil, coal and gas are non-renewable sources of energy. Wind, waves and solar energy are renewable
sources of energy. Radioactivity is the break-up of atoms naturally giving off what is called nuclear radiation
e.g. radon and uranium. Radioactive substances are used for treatment of cancer and for producing electricity in
nuclear power stations for example. Exposure to nuclear radiation causes cancer and is very harmful.
Thermometers Conserving energy is very important in today’s world. It can save us a lot of money and
allow non-renewable energy resources last longer. Insulation in our homes, attics, walls, water tanks etc. can be
insulated to reduce our heating bills considerably.
Power is the amount of work done per second.(W).
Temperature is a measure of how hot something is and is measured in degrees Celsius. The freezing point of
water is by choice OoC and the boiling point of water is by choice 100 0C. These points are marked on a
thermometer by putting a new thermometer in boiling water and then in melting ice and the 0 and 100 marks are
made. It is then divided into a 100 parts to get the Celsius degrees. Thermometers are based of the fact liquids
expand when heated. There are two types of thermometer. The mercury thermometer which has a wide range,
doesn't stick to the glass and can be easily seen. It is expensive and cannot measure very low temperatures. The
alcohol thermometer is very sensitive, cheaper and can measure very low temperatures. It cannot measure
temperature above 78oC, sticks to the glass and has to be dyed. The clinical thermometer is a mercury
thermometer used to measure body temperature. It has a short range and a constriction above the bulb. It must be
shaken before use to return the mercury to the bulb.
Effect of Heating
Solids, liquids and gases expand when heated.
Exp. To show solids expand when heated
1. Get a metal ball and ring .
2. The ball just fits through the ring when it is cool
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4.
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Heat the ball strongly.
The ball does not fit through the ring.
Metals expand when heated.
Exp. To show that liquids expand when heated.
1. Fill a flask with a glass tube full of water and heat as shown in the
diagram.
2. Heat the water. The water rises up the tube.
3. This shows liquids expand when heated.
Exp. To show gases expand when heated.
Heat
1.
Heat the flask opposite as shown at the top
2.
3.
.Bubbles are seen in the water in the beaker.
This shows gases expand when heated.
Heat here
Flask
of
air
glass tube
bubbles
Beaker
of
water
Boiling point is the temperature at which a liquid turns into a gas. Melting point is the temperature at which a
solid turns into a liquid.
Boiling point and melting point depend on pressure. The higher the pressure the higher the b.p. or m. p. M. p.
also depends on purity, impurities lower the melting point.
Exp. Measure the melting point of ice.
1. Place crushed ice in a funnel over a beaker.
2. Record the temperature every minute.
3. Note there is no temperature change until all the ice melts
4. Continue heating and recording.
5. Note there is no temperature change as the water changes into steam.
6. Three and five are the latent heat.
Sublimation is the changing of substance from a solid to a gas without ever becoming a liquid. e.g. Ammonium
Chloride or Iodine.
Latent heat is the heat used changing a solid to a liquid or a liquid to a gas which does not cause a rise in
temperature.
Exp. Showing latent heat
1. Heat a beaker of ice.
2. Place the bulb of the thermometer in the ice.
3. Note the readin on the thermometer when it is surrounded by melted ice.
4. For pure water this is 0 oC.
Exp. Measure the boiling point of water.
1. Setup a tripod wire gauze and Bunsen burner to heat a beaker of water.
2. Place the bulb of a thermometer just above the level of the boiling water.
3. Record the highest temperature reached.
4. The boiling point of pure water is 100oC.
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Conduction is the movement of heat through a substance without the movement of the substance. The rate of
conduction is different for different substances. Water is poor conductor of heat. Insulators are substances which
are poor conductors .
Exp. To show conduction in various substances
1. Stick matches to ends of different rods with wax
2. The other end of each rod is stuck into a box.
3. Fill the box with boiling water.
4. Note the time for each match stick to fall off.
5. The quickest is the best conductor.
Exp, To show water is poor conductor.
1. Put ice in the bottom of a test tube full of water.
2. Hold the ice down with a weight
3. Heat the top of the test tube.
4. The water boils without melting the ice.
Exp. To show the effect of insulation
1.
2.
3.
4.
Pour boiling water into two beakers
One beaker is insulated with cotton wool
Record the temperature of both every 5 minutes.
The insulated beaker is the hottest after 30 mins.
Convection is the movement of heat due the movement of heated particles of a substance. Convection takes
place in gases and liquids only Why?.
Exp. To show convection in liquids
1. Fill a round bottomed flask with water
2. Drop in one potassium permanganate crystal.
3. Heat the flask.
4. Observe the convection currents, the dye travels in a circular fashion
Exp. To show convection in gases
1. Light the candle in the box as shown in the diagram
2. Put a smouldering piece of string over the chimney.
3. Note how the smoke is drawn through the box.
4. This shows convection in gases.
smoldering
string
chimney
window
Direction of
the smoke
candle
Radiation is the way in which energy travels out from a hot object in straight lines in all directions. Dull or
black surfaces are better absorbers and radiators of heat than bright or white surfaces. The thermos flask stops
heat loss by conduction and convection because of the vacuum between the walls and stops radiation due to the
silvered walls.
Exp. To show a dull surface is a better absorber than a bright surface
1. Stick a penny to a dull black can with Vaseline
2. Repeat 1 for a glossy white can
3. Place both equal distances from a heater
4. Record the time for the pennies to fall
5. The penny on the black can falls first
6. This proves a dull black surface is a better absorber
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Light and Sound
Light is a form of energy. This can be shown by shining light on the solar cells of a calculator. The light is
changed into electricity thus working the calculator. Luminous objects make their own light e.g. Sun. All other
objects are non-luminous. Light travels in straight lines.
Light
When light 'bounces' off a surface it is said to be reflected. Shadows are caused because light travels in straight
lines.
An eclipse of the Sun occurs when the moon comes between the earth and the sun and blocks the light.
Reflected light from a rough surface is called diffuse reflection. Reflected light form a smooth surface is called
regular reflection.
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A periscope uses mirrors to see over the top of tall objects.
Applications of reflection
1. periscopes.
2. Reflectors for safety on cars, bicycles.
3. Make-up and shaving mirrors.
4. Curved mirrors in headlights and spotlights.
5. security mirrors in stores and train stations.
6. Moving mirrors in lighthouses.
Refraction is the bending of light rays as it passes from one type of substance into another.
Exp. To Demonstrate Refraction
1. Place a coin in the bottom of a cup.
2. Move the cup along a ruler until the coin just cannot not be seen
3. Fill the cup with water.
4. The coin can now be seen.
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A converging lens brings light rays together. It is curved outwards. A diverging lens spreads light rays apart. It
is curved inwards.
Dispersion is breaking up of white light into a spectrum. Dispersion can be demonstrated using a prism.
Use of refraction.
1. Lenses in telescopes, microscopes, cameras and spectacles.
2. Mirages.
3. Refraction is used in forensic science to identify types of glass.
4. Refraction is the cause of colours and sparkle of diamonds.
Waves
A wave transfers energy from one point to another. The substance the wave travels through is called the
medium. The distance from the crest of one wave to the crest of another wave is called the wavelength ()
measured in metres. The Frequency (f) is the number of waves passing a particular point in one second
measured in Hertz (Hz). The amplitude (A) is the maximum displacement of the medium (metres). The speed =
Frequency x wavelength measured in m/s.
Sound
Sound is a form of energy as can be seen in the moving cone of a loudspeaker. Sound is caused when something
vibrates and therefore must have a material to travel in. A noise is a random collection of waves of different
wavelength. A note is a regular wave of only one wavelength. The pitch of a note depends on its frequency.
Echoes are caused by reflected sound. Reflection of sound shows that sound is a wave.
Exp. To show sound needs a medium to travel in.
1. Set up a sealed bell jar with a ringing bell
inside
2. Use a pump to remove the air and create a
vacuum.
3. With no air no sound can be heard
4. Sound must have a substance to travel in.
Sound travels about 340m/s in air.
To pump
bell jar
Bell
Electricity and Magnetism
Charge is stored electricity. You can charge a body by friction i.e. rubbing it. A charged body can attract things
for example a charged pen attracting pieces of paper. There are two type of charge positive charge and negative
charge. Like charges repel and unlike charges attract. Static electricity is explained in terms of atoms, atoms
which have lost electrons are positively charged and atoms which have gained electrons are negatively charged.
s the leaves to diverge(rise).
Conductors allow electricity to flow through them, insulators do not.
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Uses of static electricity.
1. Removing soot from chimneys to stop pollution.
2. In photocopying and spray painting.
Problems caused by static electricity.
1. Danger near flammable liquids, like when refuelling aeroplanes.
2. Lightning.
3. Handling computer parts.
4. Small electric shock s due the build up of static electricity on cars, clothes and television screens.
Lightning is an everyday example of static electricity.
As a protection against the build up large charges on buildings, aeroplanes, etc they are usually earthed. For
buildings lightning conductors are used, which consists of a sharp metal spike at the top of the building
connected to a copper strip going down into the ground.
Earthing means connecting an object to the ground with a conductor so that the electricity goes safely to the
ground doing no damage to the object.
An electric current is the flow of charge, measured in Amperes (A). Potential difference (voltage) is a
difference in 'electrical pressure' between two points, measured in volts(V). If there is a potential difference
between two points and they are connected by a conductor then a current will flow.
A cell is a device for making a potential difference between two points by means of chemical reaction. Direct
Current (D.C.) flows in one direction only whilst alternating current (A.C.) changes direction every one
hundredth of a second.
Electrical symbols
Below are some common symbols for drawing circuit diagrams in electricity.
Exp. To find if a substance is a conductor or an insulator
Battery
Light
Bulb
A
1.
2.
3.
4.
5.
B
Test
substance
Set up a circuit with a battery and a bulb.
Leave a break in the circuit labelled A and B.
Connect various substances to A and B
The bulb only lights if the substance is conductor.
In general metals are good conductors.
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A resistor is a substance which reduces or stops the flow of current. measured in ohms (). Resistors whose
resistance can be varied are called variable resistors or rheostats. Resistors are used in radios, televisions and
all types of electrical appliances. Resistors can be connected in two ways, in parallel i.e. side by side or in series
i.e. one after another. Ohm's Law states that at a constant temperature the voltage across a conductor is
proportional to the current flowing through it. V = I . R
Exp. To measure Current.
1. Setup as shown in the diagram.
2. Close the switch.
3. Record the current reading on the ammeter.
4. Show that swapping the position of the ammeter and the switch does not change the current.
Exp. To measur potential difference (Voltage)
1. Set up a circuit as shown in the diagram.
2. Close the switch and record the reading on the voltmeter.
3. Replace the resistor with other resistors and record their voltages.
Exp. To measure resistance.
1. Set up a multimeter to read resistance.
2. Connect the resistor between the ends of the leads of the multimeter.
3. Record the resistance and repeat this for different resistors.
Exp To prove Ohm’s law
Method
1. Set up as shown in the diagram
2. Record the voltage and the current.
3. Adjust the rheostat and repeat 2.
4. Repeat 3 several times.
5. Draw a graph of voltage against current.
Diagram
Result
Rheostat
A
V/volts
I/amps
V/I = R Ohms
V
Resistance
Graph
V
Volts
Water
I/amps
Conclusion
The straight line graph proves Ohm’s Law.
An ampere(A) is a measure of how much current is flowing in a wire of an appliance. A volt(V) is a measure
of the power of a battery of power supply, it is the force which drives the current. A watt(w) is measure of the
amount of electrical energy converted in other forms of energy in one second. One kilowatt(kW) = 1000 W A
kilowatt-hour is the amount of electrical energy converted in other forms of energy in one hour at a rate of 1000
J/second. No. of kWh(units) = no. of kilowatts x no. of hours.
A fuse is a device which protects electrical appliances, if the current gets too high it melts, breaking the circuit
thus switching of the appliance.
Exp. To demonstrate the action of a fuse.
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1.
Set. up a circuit with as shown in the diagram.
2.
Increase the power in steps of 1V
3.
Note when the current is too high the fuse goes red hot and melts
A
Fuse
All appliances with a metal body must be earthed. A earth wire is to protect people from an electric shock. It is a
length of copper wire connected to the ground.
A plug has three wires, earth (green and yellow), live (brown) and neutral (blue). Power = Voltage x Current.
Also Power = Resistance x (current)2.
Effects of an electric current.
 Electric current has a heating
 Magnetic
 chemical
Electrical power (watts)= voltage x current
Exp. To show the heating effect of an electric current.
1. set up a circuit as shown
2. Set the current and note the temperature of the
water after five minutes
3. Increase the current and repeat two
4. While current flows the temp of the water
increases, so electricity has a heating effect.
thermometer
Coil
Water
A circuit is a number of electrical components joined together. It must include a battery.The greater the voltage
the more current that can be driven around the circuit. If there is any break in the circuit the current stops. A
switch is a device for opening and closing a circuit. Circuit diagrams are used to draw circuits using symbols to
represents the parts (refer to the electricity section in the physics)
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If there are two bulbs they can be connected in series i.e.
one after the other ( however if one bulb blows they all
go out), or in parallel, i.e.side by side,if one bulb blows
it doesn't affect the rest.
Resistors either reduce or stop the flow of current.
Resistance is measured in ohms. Bulbs are just resistors
which convert some ot the electricity into light.
A light Dependent Resistor (L.D.R.) is a resistor whose
resistance depends on the amount of light reaching it,
made of cadmium sulphide. They are used for light
controlled switches.
Exp. To investigate an L.D. R.
1. Set up a circuit as shown in the diagram.
2. Use an ohmmeter to measure the resistance of the L.D.R.
3. Record the resistance in the dark, in the shade and in bright light.
The brighter the light the smaller the resistance.
Diodes and light emiting diodes
A diode is a device which allows current to flow in one direction only. A diode has a negative end (cathode)
which is marked with a silver band and a positive end (anode). When a diode is connected with its negative end
to the negative of the battery it is said to be forward bias and a current flows. If the positive end is connected to
the positive of the battery it is said to be reverse bias and no current flows through it.
Exp. Investigating diodes.
1. Set up each circuit as shown in the diagram.
2. In circuit 1. the lamp lights, the diode is forward bias.
3. In circuit 2 the lamp does not light, the diode is reverse bias.
A rectifier is a device for a.c. current to d.c. current.
Some devices like radios, televisions and computers will only work with d.c. and mains electricity is a.c. A single
diode can be used as a half wave rectifier, more diodes are needed for full rectification.
Exp. To show the operation of a half wave rectifier.
Set up as shown in the diagram. Using a CRO attached to the d.c. output it is possible to view the rectified
current. For half the a.c. cycle the diode is reverse bias an no current flows, for the other half it is forward bias
and current flows.
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A light emitting diode (l.e.d.) is a diode which gives out light when a current flows in it.
The flat side and the short wire is the negative end.There are red, green and yellow. It must
be in forward bias to light. L.e.d.'s are used widely as indicator lights on electrical
equipment, digital displays etc.L.e.d.'s use only very small currents and thus must have a
resistor in series with them to limit the current.
The following circuit shows the operation of l.e.d.
Two l.e.d.'s in parallel may be used as a battery polarity tester. as shown in the following
diagram. If terminal A is positive then the red l.e.d. will light whilst if terminal B is positive
the green l.e.d. will light.
The following circuit shows how l.e.d.s can be used to
make a water level detector. Set up a circuit as shown
in the diagram.
Add water to the beaker until it touches the wires.
The l.e.d. lights.
This shows how a circuit can be switched on
automatically.
Note: This could be used to monitor the water level in a water storage tank. Thermostats are automatic switches
for heating circuits.
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Magnetism
The elements iron, nickel and cobalt have magnetic properties. A permanent magnet is always magnetic,
whilst an electromagnet is a magnet only when electricity flows through it. A freely swinging magnet always
comes to rest in a north-south direction. The end pointing north is called a north pole and the other end is
called a south pole. Like poles repel and unlike poles attract.
The space around the magnet where magnetic forces can be experienced is called a magnetic field. Magnetic
field lines always go from north to south. The earth has a magnetic field which behaves as if the earth had a bar
magnet in its centre. Once an electric current flows a magnetic field is created.
A compass is a small bar magnet that can move freely and so always points in the direction of the north pole.
Exp. To show the magnetic field of a bar magnet
1.
2.
3.
4.
Place a bar magnet under a sheet of paper.
Sprinkle iron filings over the paper.
Use a plotting compass to find the direction of the lines of force.
The result should be as shown in the diagram
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Eolaíocht J.C.E.
N
D.Mac an Aircinn
S
sheet of paper
Exp. To show the magnetic effect of an electric current.
1. Place an ammeter and a battery in a circuit.
2. Place a compass near one of the wires
3. Notice the effect on the compass
4. A current creates a magnetic field
to a battery with a piece of white card around the wire. Iron filings are sprinkled on the card to show the field.
A magnet can be made by placing a piece of steel in a solenoid, this is called an electromagnet
Uses of magnets include compasses, motors, speakers, telephones, circuit breakers, metal detectors, door
catches etc.
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