Download Physics Revision Notes

Measurement
Measurement of length
Length can be measured by,
 A metre stick (straight lines)
 An opisometer (small curved lines)
 A trundle wheel (large curved lines)
 A vernier callipers (diameters and small
widths)
Length is measured in mm, cm, m, km.
Experiment: To measure the length of a curved
line

Roll the wheel of an opisometer back to
the pointer.

Place the pointer at the start of the
line.

Roll it carefully along the line, to the
end.

Now place the pointer on the zero of a
metre stick and roll it backwards until
the wheel stops at the pointer.

The reading on the metre stick is the
length of the line.
Measurement of area;Area is how much ground
something covers. Area is measured in area
mm2, cm2, m2, km2.
Experiment: To find the area of your hand

Place your hand, fingers together,
on squared paper.

Draw its outline on the page.

Count all of the squares which are


completely inside or more than ½
inside the outline of your hand.
Discount any squares which are less
than ½ inside the outline of your
hand.
Multiply this number by the area of
one square. This is the area of your
hand.
Measurement of volume;Volume is the amount
of space occupied by an object. Volume is
measured in mm3, cm3, m3.
Density
The mass of an object is the amount of
matter in it.
The density of an object is the mass of
1cm3 of it. The unit of density is
g/cm3 (grams per cm3).
Experiment: To measure the volume of a regular
rectangular block

Measure the length, width and
height of the block.

Multiply the measurements together.
Density 
Mandatory experiment: To find the density of a
liquid (water)
mass(g)
volume(cm 3 )
Mandatory experiment: To find the density of a
regular rectangular block
Experiment: To find the volume of an irregular
object (a stone)
Method 1
10.5g
Block

65
cm3
40
cm3
10.5g

Stone
Before
After
 Add water to a graduated cylinder as
shown.
 Gently slide in the stone.
 The water level rises by 25 cm3.
 The volume of the stone is 25 cm3.
Method 2

Fill the overflow can to the point of
overflowing.

Lower the stone gently into the
water (use a thread).

The stone will displace its own
volume of water.

The water which collects in the
graduated cylinder is the volume of
the stone.


Find the mass of the block with an
electronic balance.
Find the volume by multiplying
l x b x h.
Density 
mass(g)
volume(cm 3 )
Mandatory experiment: To density of an
irregular shaped object, such as a stone.

Find the mass of the stone with an
electronic balance.

Find the volume with an overflow can or
graduated cylinder (see chapter 37).
Density 
mass(g)
volume(cm 3 )
Graduated
cylinder
Over flow can
10.5g
Find the volume of the water by
reading the side of the graduated
cylinder.
To find the mass of the water make
two measurements, (i) Get the mass
of the graduated cylinder. (ii) Get
the mass of the graduated cylinder
and the water.
Density 
mass(g)
volume(cm 3 )
Flotation - an object will float in water if its
density is less than that of water (1 g/cm3) and
will sink if its density is greater than the density
of water.
peed, Velocity and Acceleration
1. Speed is the distance travelled by an object
per unit time. This can be written
mathematically as,
Speed 
Distance travelled
Time taken
Example: If a man walks 4 km in 1 hour,
what is his average speed, in m/s?
Answer:
4000m
Speed 
 1.11m/s
3600s
To use the speed formula, it is sometimes
useful to consider the triangle below.
If you want to ‘find the distance travelled’,
cover the ‘D’ and the answer is S x T.
Speed, Velocity and Acceleration

. Speed is the distance travelled by
an object per unit time. This

If you want to ‘find the time taken’
for a journey, cover ‘T’ and the
answer is D/T.
3. Acceleration is the change in velocity per
second. This can be written mathematically as,
Change in velocity
Accelerati on 
Time taken
Example: The velocity of a car changes from 30
km/hr to 60 km/hr in 5 seconds, what is its
acceleration?
Answer:
Accelerati on 
 6km/hr/s
S
x T
60  30 30

5
5
Pressure



exerted by a liquid
Liquids exert pressure.
This pressure increases with depth.
The pressure in a liquid is the same
in all directions.
Atmospheric pressure
Above us we have 15 km of air pressing down
on the surface of the earth. This air, like a
liquid, exerts a pressure which is called
atmospheric pressure.
To demonstrate atmospheric pressure –
Method 1
Pressure
The pressure exerted by an object is the force (in
Newtons) which it exerts on 1m2.
Mathematically, this maybe written as:
Pressure 
D
Method 2 – The crushed can experiment
2. Velocity is the speed in a given direction.
30 km/hr would be the speed of a car.
30 km/hr due south would be its velocity.
Force
Area
Cardboard
Glass of water
 Heat a small volume of water in a tin can
until it starts to boil.
 As soon as steam is seen leaving the can,
remove the heat and seal the can with a
stopper.
 Allow the can to sit on a bench to cool.
 As it cools, the steam in the can
condenses to water and a vacuum is
created.
 The creation of this vacuum means the can
will be crushed by the atmospheric
pressure.
Measuring atmospheric pressure
The pressure of the atmosphere is measured
with a barometer. There are two main types
of barometer, a mercury barometer and an
aneroid barometer.
[unit  Pascal (Pa)]
The connection between pressure and force
If you press down on the flat
end of a thumb-tack with your finger, applying a
certain force, you will experience no discomfort.
If, however, you press, on the same thumb-tack,
at the pointed end, with the same force as before
you will feel considerable pain.
Why does the same force, applied to the same
object, have such different results?
The force, in the first case, is spread over a larger
area than in the second case and therefore is not
as keenly felt.
Heat
Atmospheric pressure
 Fill a glass to the rim with water.
 Cover it with a cardboard.
 Hold the cardboard in place and turn the
glass upside down.
 The water remains in the glass and the
cardboard stays in place.
 Explanation; the pressure of the
atmosphere, acting upwards, holds the
water in the glass by pressing the
cardboard upwards. This demonstrates
that atmospheric pressure acts upwards as
well as downwards.
What can we tell from atmospheric pressure?
1. Predict the weather – high atmospheric
pressure means fine, calm, sunny
weather, with no winds. Low pressure
means unsettled, windy, wet weather.
Lines joining points on a map with similar
atmospheric pressure are called isobars.
If the isobars are close together the
winds will be strong.
2. Measure altitude (height above sea level)
– The higher you go above sea level the
lower is the atmospheric pressure. An
altimeter is a barometer which is
adapted for making measurements of
height-above-ground.
Force, Work and Power
A force is anything which changes the velocity
or shape of an object. Forces are measured in
Newtons (N). There are different kinds of
forces – push, pull, friction, electric,
magnetic.
Forces always occur in pairs.
Disadvantages of friction

Shoes wear out.

Tyres wear out.

Machine parts wear out.

Friction burns from a rope.
Power is the rate at which work is done. It is
measured in J/s (joules per second), or Watts.
Experiment: To investigate the force of friction
Example; A man lifts a 200 N object from the floor to
a table which is 750 cm above the ground, in 0.5
seconds. What is his power?
Block
Friction is the force which opposes the motion
between two objects in contact.
Examples of friction:
1. If you rub two pieces of sand paper
together, there will be a very large
force of friction between them.
2. The friction between rubber soles
on your shoes and the ground gives
you grip and stops you slipping.
Preventing friction
To prevent or reduce friction we put
lubricant between the two surfaces in
contact. Grease and oil are common
lubricants.
Advantages of friction

The force of fiction between your
shoes and the ground, prevent you
from slipping.

Friction helps tyres to grip the
road.

Friction generates heat when you
rub your hands together.
Pull
20 N
Example 1: When a balloon is released, the
air shoots out the back with a certain force
and the balloon travels in the opposite
direction with an equal but opposite force.
Example 2: When a gun is discharged, the
bullet flies in one direction and the gun
moves in the opposite direction with an equal
force.
Newton-meter
Bench top







Set up the apparatus as shown.
Fix sand paper to the base of the
block and onto the bench surface.
Pull the block along the bench
surface with the spring balance.
Read the force applied to the block
from the side of the Newton-meter.
Repeat the experiment but use no
sand paper.
Repeat the experiment with oil
between the block and the bench.
You should find that the force
needed to move the block is greatest
for the sand paper because of the
large force of friction and smallest
for the oil.
Work is done when a force moves an object.
Work is measured in joules (J).
Work = Force (N) x Distance (m)
Example 1:
If a man uses a force of 300 N to move a wheel
barrow a distance of 100 m, what work has the
man done?
Work = 300 N x 100 m =
Work done(J)
Time taken(s)

Now draw a graph of Extension

The graph should look like this,
versus weight placed on the spring.
Answer:
Work done = (200)(0.75) = 150 J
Power = 150J/0.5s = 300 W
Extension
Mandatory experiment: To investigate Hooke’s law of
spiral springs
0

Metre
Spring
Weights
Pan





Set up the apparatus as shown.
Measure the length of the spring and pan
before any weights are added.
Now add a weight to the pan.
Measure the extension of the spring with
the metre stick.
Repeat the procedure by adding more
weights and recording the extension each
time.
Record your results in a table, as shown.
Weight
on the spring
0
(N)
The graph is a straight line
through (0,0). This means that
the extension is directly
proportional to the force applied
to it.
stick


Answer;
30,000 J
Power 
Weight
(N)
Extensi
on (cm)
Note; When recording the force
on the spring, you multiply the
mass by 9.8 e.g. 200g (0.2kg)
should be recorded as
0.2 x 9.8 = 1.960 N.
A lever is a rigid body which is free to rotate
about a fixed point called the fulcrum.
The law of the lever - When a lever is balanced the
sum of the clockwise moments* is equal to the sum of
the anti-clockwise moments.
Pin
Everyday examples of levers
*The moment of a force = (Force) x (perpendicular
distance from the force to the fulcrum).
LLoad
Example 1: Is the metre stick below balanced?
Effort
Wheel barrow
Fulcrum
Load
Fulcrum
Centre of
gravity
Weight
Equilibrium and the stability of objects
When an object is balanced and not moving it is
said to be in equilibrium. There are three states
of equilibrium,
 Stable equilibrium – An object is in stable
equilibrium if moving it raises its centre of
gravity.
Experiment: To find the centre of gravity of an
irregular piece of cardboard

Hang the cardboard from a pin on
a stand, so that it can swing
freely.

Attach a string with a weight as
shown on the diagram below.

Draw a line behind the string to
mark its position.

Move the cardboard to a new
position and repeat the procedure.

The centre of gravity is where the
two lines cross.
Stable equilbrium
30
cm
cm
| | | | | | | | | | |
| | | | | | | | | |
Unstable equilibrium
The Centre of Gravity (cog) is the point
through which all of the weight of a body
appears to act. This is usually its balancing
point.
40
Neutral equilibrium
 Unstable equilibrium – An object is in
unstable equilibrium if moving it lowers its
centre of gravity.
 Neutral equilibrium – An object is in
neutral equilibrium if moving it has no
effect on the centre of gravity.
Objects in stable equilibrium will have a wide
base and a low centre of gravity. When designing
objects this fact must be kept in mind.
30
40
Answer:
Left-hand side (anticlockwise) Right-hand side
Moments  Force  Distance Moment  Force  Distance
 30N  0.4m
 12 moments
 40N  0.3m
 12 moments
Since the moments are equal on both sides, the lever
is balanced.
Example 2: Where on the metre stick must the
weight, 20 N, be placed if it is balanced?
?
40
cm
| | | | | | | | | | | |
| | | | | | | | |
15
N
Answer:
Left-hand side
20
N
Right-hand side
Moments  Force  Distance
 (15N)(0.4m )
 6 moments
Moment  Force  Distance
 (20N)(x)
 20x
x
6
 0.3m  30cm
20
Light is a form of energy. We can say this because it can be
made to do work.

Solar cells produce electricity from sunlight.

Plants make food energy from sunlight in
photosynthesis.

Luminous objects are those which give out their own light, e.g.
the sun gives out its own light.
Non-luminous objects do not give out their own light but only
reflect light, e.g. the moon reflects light from the sun.
Mandatory experiment; To show that light travels in straight
lines.
Ray box
3 Cardboards with holes
Experiment : To show how shadows are formed.
Object
Ray box
screen
Line up three pieces of cardboard so that the holes in the
middle of the cardboards are in a straight line.
Turn on the ray box.
As long as the holes in the cardboards are in a straight line
light will shine on the screen.
This shows that light travels in a straight line.
Set up the apparatus as shown.
The ray box emits a beam of light.
Part of the beam hits the object and is stopped.
Part of the beam hits the screen.
Where the beam is stopped, a shadow is left on the
screen, the shape of the object.
Important shadows

When the moon comes between the earth and the
sun, a shadow of the moon falls on the earth. This is
called a solar eclipse (because the sun’s light is
blocked out).






Dispersion is the name given to the splitting of white light into
its seven colours.
Example1: When sunlight passes through a shower of rain the
seven colours separate out from each other to give a rainbow
effect.
Refraction is the bending of a light beam, from its original
pathway, as it passes from one medium into another (from air
to water or from water to air).
Refracted
Experiment: To produce a spectrum of white light.
Ray
box
Light
beam
box
Glass block
Prism of
glass
Screen





Set up the apparatus as shown.
A beam of light hits the glass prism.
As it passes through the glass the colours in the light
are dispersed (scattered).
The screen should show a rainbow effect.
The colours of the white light are red, orange,
yellow, green, blue, indigo and violet (Richard of York
gave battle in vain).
Set up the apparatus as shown.
The ray box emits a beam of light.
When the beam hits the glass block, it passes through,
but it changes direction, and exits the block at a
different angle.

This change in direction is due to the refraction of the
light beam.
Importance of refraction
In lenses, mirages, rainbow effect, extra daylight each day.



Light beam
Mirror
box
beam
Light
beam
Ray
When the earth comes between the sun and the
moon, a shadow of the earth falls across the moon.
This called a lunar eclipse.
Mandatory experiment: To show that light can be reflected.
Ray
Experiment To show refraction of light.
Screen





Set up the apparatus as shown.
The ray box emits a beam of light.
Place a small mirror in front of the beam.
The direction of the beam will change.
The light beam has been reflected.
Important uses of reflection of light
1.
Periscopes are used to see over tall objects.
2. Reflective mirrors in cars.
3. Shaving and make-up mirrors.
4. Microscopes.
5. Security mirrors.
Sound is a form of energy
How do we hear sounds?

When a sound is made (hammer hitting a nail) the
air molecules start to vibrate.

These vibrations are passed from molecule to
molecule until they reach your outer ear.

The outer ear acts as a funnel and directs these
vibrations to the eardrum.

Once the eardrum starts vibrating, a signal is sent
to the brain and the sound is registered.
How fast does it travel?
Sound travels at a speed of
340 metres per second (in air)
1400 m/s in water
5,000 m/s in concrete.
Speed of light = 300,000,000 m/s.
Experiment: To show that sound is a form of energy.
Answer:




Hold the foam ball near the speaker of a stereo
system when it is playing loud music.
The ball should move because of the sound
vibrations.
If sound can move objects then it is able to do
work.
This makes it a form of energy.
Alarm
Bell
clock
Question: If an observer hears the sound of thunder three
seconds after he sees the flash of lightening, how far is the
lightening from the observer?
To vacuum
Distance
Time
 Distance  Speed  Time
Speed 
Speakers
Foam ball on a light string
Experiment: To show that sound needs a to travel through a medium
 Distance  340  3  1020m
 The trhunder is 1.02 km away.





Start the alarm bell ringing on the clock.
Turn on the suction pump.
The air is sucked out of the bell jar.
A vacuum has been created.
The alarm bell can still be seen to be working but no
sound will be heard.
An echo is a reflected sound.
Ultrasound waves (sound of very high frequency) are used in
various instruments to locate objects or places. A machine sends
out a burst of ultrasound waves and times how long it takes for the
sound to bounce off an object and return.

In medicine, ultrasound machines are used to ‘see’ inside
the body and look at organs or even a baby in the womb.

Fishing vessels use ultrasound to locate the seabed and
shoals of fish.

Doctors use ultrasound waves to smash kidney stones so
that they can be passed without the need for surgery.
Loudness of sound
The decibel (dB ) is the unit used to compare the loudness of
sounds. Jet plane (120dB), lawnmower(80dB), talk (50dB).
Magnetism
A magnet is a metal which attracts other pieces
of metal.

Only three metals can be made into
magnets, or will be attracted by
magnets. These metals are nickel
(Ni), iron (Fe), copper (cu). In fact,
most magnets are mixtures of these
metals.

The first magnets were magnetic
rock called lodestone, used as far
back as 500 b.c.

Magnets have two poles, a north and
a south pole.

Like poles repel,Unlike poles attract.

Magentic field – is an area around a
magnet where a magnet exerts an
influence.
Experiment: To show the magnetic field of a bar
magnet (method 1)
Mag
Sheet of paper

Place a bar magnet on a bench.
Cover it with a sheet of paper.
Sprinkle iron filings over the sheet.
The filings will line up along the
magnetic field lines.
The magnetic field of the magnet
has become ‘visible’ (see diagram).
Experiment: To show the magnetic field of a bar
magnet (method 2)





Place a magnet on a sheet of paper.
Place a number of plotting compasses
near the magnet so that the pointers
follow each other as shown below.
Mark the positions of the dots with
a pen.
Mark the positions of the dots with
a pen.
Remove the plotting compasses and
join the dots to form one of the
field lines.
Repeat this procedure several times
to construct more field lines.
Experiment: To investigate the behaviour of
magnets.



N







Suspend a magnet from a piece of
light thread, so that it can swing
freely.
Bring another magnet close to this.
If two north poles are brought near
each other, the magnets repel.
Same result, with two south poles.
If a south pole is brought a near a
north pole, the magnets will attract.
Uses of magnets

In speakers.

Fridge doors.

Electric motors.
Earth’s magnetic field
The earth behaves like a large bar magnet,
with two poles, one at the north and one at
the south. The south pole of this imaginary
magnet is in the northern hemisphere and the
north pole is in the southern hemisphere. This
is why the north pole of all compasses point to
the north.
Storing magnets

Magnets are stored in pairs, with
opposite poles together.

Two pieces of iron are placed at
either end, as keepers. These close
the magnetic fields and so preserve
the magnetism.

A piece of cardboard is place
between the magnets as a spacer.
Static electricity
Static electricity is electric charge which is
stationary. This kind of charge usually builds
up on plastic materials and fabrics. Since
they are insulators they don’t allow electricity
to flow through them.
 Static charge builds up on materials when
they are rubbed together.
 Electrons are knocked off one material and
onto the other.
 When a material loses electrons it becomes
positive.
 When it gains electrons it becomes
negatively charged.
 When polythene is rubbed with a cloth it
becomes negatively charged.
 When Perspex is rubbed with a cloth it
becomes positively charged.
Earthing
When a large electric charge builds up on an
object, it must be allowed to flow into the
earth, to make the object safe for us to
touch.
The charge will discharge itself, often with
violent consequences. The most dramatic
example of this is lightening. The charge on
the thunder clouds builds up to an intolerable
level.
Eventually, it will discharge into another cloud
(sheet lightening) or into the ground (fork
lightening).
Many structures and buildings are provided
with lightening conductors to avoid damage by
lightening strikes.
Experiment: To show the presence of static
electricity.
 Rub a plastic biro with a cloth. It can
pick up small pieces of paper.
 Rub an inflated balloon against your
clothes. It becomes charged and will
stick to the paint on walls and to your
clothes.
 Hold a charged biro near a thin
stream of water from a tap. The
water will move towards the biro
because water has tiny charges.
Current electricity
An electric current is a flow of electric charge.
To understand the behaviour of electricity we will look
at a simple circuit.
To show the heating effect of electric
current
Cell (power supply)
Cell (power supply)
+

+
If you disconnect one bulb, the
others remain lighting. For this
reason, parallel circuits are used in
lighting circuits in our homes.
Switch
Switch
Bulb
Bulb
When the switch is closed, electricity flows from the
cell and the bulb lights. When the switch is open, as
in the diagram above, no current flows from the cell.
There are number of quantities which you must know
to talk about electrical circuits.
Voltage (symbol is V) is the pushing power of the
power supply. It is measured in volts (V).
Current (symbol is I) is the flow of electrical charge.
It is measured in amps (A).
Resistance (symbol is R) is the ability of a substance to
resist, or slow down, the flow of electricity through a
circuit.
Ohms law states that at constant temperature the
voltage (V) is always proportional to the current (I) in a
circuit i.e.
V = I.R
Electrical Power = V.I



Close the switch and allow current
to flow through the circuit for a
few minutes.
Hold a thermometer against the
bulb.
The increase in temperature
registered on the thermometer
shows that heat has been produced
in the circuit.
To show the magnetic effect of an electric
current

Set up a circuit as above with the
switch open.

Bring a compass near any part of
the circuit wiring.

Nothing happens.

Now close the switch.

The needle of the compass will be
seen to deflect.

This happens because the all
electrical circuits are magnetic
when carrying current.
To show the chemical effect of an electric
current

Set up the apparatus as shown
below.

When electric current is flowing in
the circuit the water molecules are
broken up and form hydrogen and
oxygen gases.

Hydrogen collects at the negative
electrode.

Oxygen collects at the positive
electrode and is only ½ the volume
of the hydrogen gas.
Mandatory experiment: To distinguish
between conductors and insulators
Cell (power supply)
Bulbs in series
+
-
x
Bulb
When the bulbs are connected in series,
 The more bulbs which are connected
the dimmer the light given out by each
one. This is because the voltage of the
battery has to be divided amongst a
greater number of bulbs.
 If you disconnect one, all the lights
will go out.
Bulbs in parallel
When bulbs are connected in parallel as
shown below,
 All the bulbs will shine equally brightly
and there will be no dimming effect if
you add more bulbs. This because all
bulbs have the same voltage across
them.
 Set up the apparatus as shown.
 Connect a variety of substances across
the wires at ‘x’.
 If the bulb lights,the substance is a
conductor, if not, the substance is an
insulator.

Mandatory experiment: To verify Ohm’s Law
Ammeter
A
V
Voltmeter
Variable
resistor
Resistor









Set up the apparatus as shown in the
diagram.
Record the current flowing through the
resistor by reading the ammeter.
Record the voltage across the coil by reading
the voltmeter.
Adjust the variable resistor to give a new
voltage across the resistor.
Record this new voltage.
Record the current reading from the
ammeter.
Repeat this procedure for several different
values of voltage and current.
Make a table of your values.
Plot a graph of Voltage versus Current.
e
Current

Direct current (d.c.)

This type of current flows in the same
direction all the time.

The power supplied by a battery is direct
current.
Advantages of alternating current over direct
current
 The ESB can transport it over long
distances without losing power.
 It can be converted to d.c. easily when
needed for appliances in the home.
Electricity is supplied to your home by two
cables;
 The live cable (brown colour) and
 The neutral (blue colour).
A third type of cable is found in household
circuits;

The earth wire (green and yellow)
which is connected to the ground via
a galvanised rod outside the house.
This is a safety cable attached to all
major circuits and to appliances with
metal bodies.
Voltag

Electricity in the home
There are two types of current electricity;
Alternating current (a.c.)
 Changes its direction of flow, constantly.
 The electrical supply to your home, provided
by the ESB, is alternating.
 The supply is called a 50 Hz (50 hertz)
supply. This means that the direction of
the current changes 50 times every
second.
A straight line through (0,0) proves that the
voltage is proportional to the current.
If you divide V by I you should get the same
value for R each time.
Safety measures in the home
1. Fuses
A fuse is a thin metal wire housed in a
ceramic container. In the event of a fault
developing and too large a current flowing,
the fuse wire melts preventing any major
damage or fire. When using a fuse a number
of precautions must be observed,
The fuse must be of the correct rating.
The fuse rating is the maximum
current that the fuse can carry
without melting.
The fuse must be in the live side of the
circuit for safety.
Fuse
wire
Sand
Metal
caps
2. Earthing
An additional measure must be taken to
safeguard a user. All electrical
appliances, which have exposed metal
parts should be made safe to touch
even if a fault develops inside them.
This is achieved by earthing, i.e. by
providing a wire (green and yellow)
which connects the metal parts to a
metal plate or rod, sunk deeply in the
soil.
Some electrical appliances are
manufactured with an all-plastic outer
casing and do not require an earth
connection.
Wiring a plug

The live (brown) is connected to the
fuse on the right- hand side.

The neutral (blue) is connected to
the pin on the left-hand side.

The earth (green and yellow) is
connected to the top pin. This is also
the longest pin.

The earth pin, being the longest,
opens the holes of the socket and
only then can the other pins be
inserted. This ensures that the
earth, and safety pin, is always first
to be connected.
The units of electrical power
Electrical power is given by the following
equation:
Power 
work done in joules
time in seconds
The unit of power is the watt (W).
The ESB calculates the electrical power used
by your home in kilowatt hours (kWh).
A kilowatt hour is the electrical energy used
by a 1kW appliance which has been running for
one hour.
Example;
(i) Calculate the number of units of electrical
power used by a 3 kW electrical heater over 4
hours of use.
(ii) If one unit of electrical energy costs 15c,
how much will the heater cost to run, over the
four hours?
Answer;
(i) Number of units used = (3kW)(4h)
= 12 kWh = 12 units
(ii) Cost = (12)(15) = 180c = €1.80
Example;
Calculate the cost of running a 50W television
set for 10 hours.
Answer;
Number of units used = (0.05 kW)(10)
Mandatory experiment: To verify Ohm’s Law
Ammeter
A
V
Voltmeter
Variable
resistor
Resistor









Set up the apparatus as shown in the
diagram.
Record the current flowing through the
resistor by reading the ammeter.
Record the voltage across the coil by reading
the voltmeter.
Adjust the variable resistor to give a new
voltage across the resistor.
Record this new voltage.
Record the current reading from the
ammeter.
Repeat this procedure for several different
values of voltage and current.
Make a table of your values.
Plot a graph of Voltage versus Current.
Voltag
e
Current


A straight line through (0,0) proves that the
voltage is proportional to the current.
If you divide V by I you should get the same
value for R each time.
Electricity in the home
There are two types of current electricity;
Alternating current (a.c.)
 Changes its direction of flow, constantly.
 The electrical supply to your home, provided
by the ESB, is alternating.
 The supply is called a 50 Hz (50 hertz)
supply. This means that the direction of
the current changes 50 times every
second.
Direct current (d.c.)

This type of current flows in the same
direction all the time.

The power supplied by a battery is direct
current.
Advantages of alternating current over direct
current
 The ESB can transport it over long
distances without losing power.
 It can be converted to d.c. easily when
needed for appliances in the home.
Electricity is supplied to your home by two
cables;
 The live cable (brown colour) and
 The neutral (blue colour).
A third type of cable is found in household
circuits;

The earth wire (green and yellow)
which is connected to the ground via
a galvanised rod outside the house.
This is a safety cable attached to all
major circuits and to appliances with
metal bodies.
Safety measures in the home
1. Fuses
A fuse is a thin metal wire housed in a
ceramic container. In the event of a fault
developing and too large a current flowing,
the fuse wire melts preventing any major
damage or fire. When using a fuse a number
of precautions must be observed,
The fuse must be of the correct rating.
The fuse rating is the maximum
current that the fuse can carry
without melting.
The fuse must be in the live side of the
circuit for safety.
Fuse
wire
Sand
Metal
caps
3. Earthing
An additional measure must be taken to
safeguard a user. All electrical
appliances, which have exposed metal
parts should be made safe to touch
even if a fault develops inside them.
This is achieved by earthing, i.e. by
providing a wire (green and yellow)
which connects the metal parts to a
metal plate or rod, sunk deeply in the
soil.
Some electrical appliances are
manufactured with an all-plastic outer
casing and do not require an earth
connection.
Wiring a plug

The live (brown) is connected to the
fuse on the right- hand side.

The neutral (blue) is connected to
the pin on the left-hand side.

The earth (green and yellow) is
connected to the top pin. This is also
the longest pin.

The earth pin, being the longest,
opens the holes of the socket and
only then can the other pins be
inserted. This ensures that the
earth, and safety pin, is always first
to be connected.
The units of electrical power
Electrical power is given by the following
equation:
Power 
work done in joules
time in seconds
The unit of power is the watt (W).
The ESB calculates the electrical power used
by your home in kilowatt hours (kWh).
A kilowatt hour is the electrical energy used
by a 1kW appliance which has been running for
one hour.
Example;
(i) Calculate the number of units of electrical
power used by a 3 kW electrical heater over 4
hours of use.
(ii) If one unit of electrical energy costs 15c,
how much will the heater cost to run, over the
four hours?
Answer;
(i) Number of units used = (3kW)(4h)
= 12 kWh = 12 units
(ii) Cost = (12)(15) = 180c = €1.80
Example;
Calculate the cost of running a 50W television
set for 10 hours.
Answer;
Number of units used = (0.05 kW)(10)
Experiment; To show the action of a fuse
Experiment: To show the action of a diode in
(i) Forward bias
Variable power source
+
12 V
Fuse wire
Light Emitting Diodes (LED)
A LED is a diode which gives out light when
current passes through it. A LED looks like
this,
Switch
Set up the apparatus as shown.
Close the switch.
A current flows through the thin fuse wire.
Gradually increase the current delivered by
the power source.
At some point, the fuse wire will get red
hot and break.
This illustrates the operation of a fuse.
Electronic devices
Diodes
A diode is a device which will allow current to
flow in only one direction through it. A diode
looks like this,
but in a circuit it is represented by the
symbol shown below.
Light Dependent Resistor (LDR)
A LDR is a resistor in which the resistance
decreases when the light intensity increases.
This means that more current is allowed to
flow through the LDR in bright light
conditions.
Experiment: To show the action of an LDR
Set up the circuit as shown.
Close the switch.
The light bulb will light.
The diode is in forward bias and
since the current always flows from
the + to the – terminal, current will
flow through in the direction of the
arrow.
(ii) Reverse bias

Set up the circuit as shown.

Close the switch.

The light bulb will not light.

The diode is in reverse bias and allows
current through only in the direction of
the arrow.

But the current from the battery is going
in the opposite direction and cannot pass
through the diode.




+
A diode can be connected in a circuit in two
ways, forward bias or reverse bias.
Uses of diodes

To control the direction of current
in electronic devices.

To change alternating current to
direct current.
but in a circuit it is represented by the
symbol shown below.
Bulb
A
LDR
Experiment: To show the action of a LED
+
330
ΩΩ
 Set up the circuit as shown.
 Close the switch.
 The LED is in forward bias and since the
current always flows from the + to the
– terminal, current will flow through in
the direction of the arrow.
 The LED will give out light.
 The 330Ω resistor is placed in the circuit
to protect the LED against a large
current.






Set up the circuit as shown.
Shine light on the LDR.
The bulb will get brighter.
An increase in current flowing in the
circuit will also be seen on the
ammeter.
Remove the light on the LDR and the
current reading on the ammeter will
fall again.
The brightness of the bulb will
decrease.
Energy
Energy is the ability to do work. There are
many different forms of energy. Energy is
measured in joules (J).
Forms of energy
 Potential energy (P.E.) – This is the energy
which an object has because of its
mechanical condition or position above
ground e.g. a coiled spring or a hammer
held above ground.
 Kinetic energy (K.E.) – This is the energy
which a moving object has.
 Heat energy – Heat is a form of energy
because it causes things to move e.g. hot
air balloon.
 Light energy – Light is a form of energy
because it causes things to move and it
does work e.g. solar cells produce
electricity to work appliances.
 Sound energy – sound can cause things to
move e.g. feel the vibrations near a
speaker of a stereo.
 Electrical energy – Electricity can cause
things to move or do work e.g. electrical
motor.
 Chemical energy – This the energy stored in
chemicals petrol or food.
 Nuclear energy – This is the energy stored
in the nucleus of an atom.
The law of conservation of energy states that
energy cannot be created or destroyed but
changed from one form into another.
Examples of energy conversion
Light bulb – electrical energy is converted
into light and heat energy.
Radio – converts electrical to sound energy.
Energy loss in the home
Energy is lost from your home in different
ways. The main areas where heat is lost are,
floors, walls, roof, windows, draughts.
Methods





of preventing heat loss
Glass fibre on the attic floor.
Lagging the hot water tank.
Air cavity in walls.
Draught excluders on doors and
windows.
Double glazing on windows.
Energy supplies
Non-renewable sources – once used they gone
forever e.g. coal, oil, gas, turf. These are
referred to as fossil fuels. They are costly to
extract and transport, cause pollution, and
there is only 300 years (at present usage) of
known reserves left.
Renewable resources – are constantly being
replaced by nature. The main sources of
renewable energy are,

Solar - Solar panels turn sunlight
into electricity.

Hydro-electric energy – Dams hold
back water and stored potential
energy is released as kinetic energy
to turn the turbine and produce
electricity.

Wind energy – Wind mills are used to
produce electricity.

Wave energy – The movement of
large floats are used to produce
electricity.

Geothermal – The temperature of the
earth’s crust is used to heat water
to steam and produce electricity.

Biomass – Some quick-growing plants
are used to produce alcohol and
methane gas.
Solar energy

The sun is our primary source of
energy.

Plants absorb light for making food
(photosynthesis).
 Animals eat plants and obtain food energy
from digesting the food made in
photosynthesis.
 The fossil fuels which run our cars,
trucks, trains, planes, factories, homes
etc. are formed from a build up of
hundreds of millions of years of decaying
plants and animals. The energy released
when burn these fuels is a result of
photosynthesis that happened millions of
years ago.
 All of our heat energy, electrical energy,
kinetic energy, food energy comes,
either directly or indirectly, from the
sun.
The warmth of the sun drives the winds on
which wind generators depend
Nuclear energy

Nuclear energy is the energy stored
in the nucleus of an atom.

When the nucleus of an atom
disintegrates, a vast amount of
energy is released.

An uncontrolled release results in a
devastating nuclear explosion.

But controlled nuclear breakdown in a
reactor, results in huge energy
release which can be harnessed and
used to produce electricity.
Advantages of nuclear energy

In medicine, to kill cancer cells.

Sterilise food (kills bacteria).

Produce electricity.

Will not run out.
Disadvantages of nuclear energy

Waste produced by the nuclear
industry is very dangerous.

There is always a danger of
explosion.
Experiment: To compare the insulating ability of
different materials
Thermomete
rs
Beaker of
water
Polystyrene
foam
 Place two beakers of boiling water on a
bench. One is insulated the other is not.
 Take the temperature in each after 10
minutes.
 The water in the insulated beaker should
be much warmer.
 This because the insulation holds in the
heat.
 Try this experiment again but with a
different insulating material and see which
is best.
Experiment: To convert mechanical energy to
heat energy and sound energy.
Drill into a piece of timber with an electric
drill (mechanical energy).
After 1 minute, remove the drill and touch
a thermometer off the tip of the drill.
The temperature shoots up, showing that
heat energy has been produced.
The noise made by the drill shows that
sound energy is also produced.
Experiment: To convert chemical energy to heat
energy
Light a candle.
Hold a thermometer near the flame.
Record the temperature change.
The heat produced is due to the chemical
energy in the wax being converted to
heat.
Mandatory experiment: To convert chemical
energy to electrical energy to heat energy
Mandatory experiment: To convert electrical
energy to magnetic energy to kinetic energy
Cell (power supply)
Cell (power supply)
+
+
Switch
Switch
Compass
Bulb






Close the switch and allow current to
flow through the circuit for a few
minutes.
Hold a thermometer against the bulb.
The increase in temperature
registered on the thermometer shows
that heat has been produced in the
circuit.
The energy conversions which have
occurred are,
Chemical energy (in the battery) to
electrical energy (in the circuit).
Electrical energy (in the circuit) to
heat energy (in the bulb).



Close the switch and allow current to
flow through the circuit.
The electric current in the circuit is
converted to magnetic energy, as the
wires in the circuit are now magnetic.
The magnetic energy of the wires is
converted to kinetic energy when the
compass needle moves.
Mandatory experiment: To convert light energy
to electrical energy to kinetic energy
Light
Solar cell


The light hits the solar cell and is
converted to electrical energy.
The electrical energy is then
converted to kinetic when the
propeller turns.
Heat
Heat is a form of energy. The unit of heat
energy is the joule (J).
There are three methods of moving heat from
place to place.
1.
2.
3.
Conduction – this is the transfer of
heat from one place to another,
through a solid, without the
particles, of the solid, moving out of
position.
Convection – this is the movement of
heat, through a liquid or gas, by the
upward movement of heated
particles.
Radiation – this is the movement of
heat, by invisible rays, from a hot
object without the need for a
medium to pass through.
An insulator – is a substance which will not
allow heat to pass through it easily.
Examples of conduction:
Metal pots
Cooking pots are made of metal because they
are good conductors and will allow food,
placed in them, to heat-up.
A poker
A poker can get extremely hot if the end is
left in the fire. The heat will travel out by
conduction to the handle.
Examples of convection:
Electric kettle
The element is placed at the bottom of a
kettle. As the water is heated, the heated
particles rise by convection and cooler ones
take their place. In this way, all of the
water will be heated.
The effects of heating
When solids, liquids and gases are heated they
expand. The only exception to this rule is water,
between 40 and 00C. W
Mandatory experiment: To show convection in
water
Mandatory experiment: To compare the
conductivity of various metals
Coloured
water
rises
Electric immersion heater
This works in a similar way to a kettle.
Convection heaters
These are usually called radiators, but this is
not a good name for them, as they heat a
room, mostly, by convection.
All hot objects
All hot objects radiate heat, in all directions.
If you put your hand over a lighted candle
you will feel great. This is heat by
convection.
If you put your hands around a candle you
will also feel heat. This is radiated heat and
it is not as much as the convected heat.
Examples of insulators:

Fibre glass wool – used for attic
insulation.

Polystyrene – used for burger boxes,
pizza boxes (keeping food hot).

Polystyrene board – used for wall
insulation to prevent heat being lost from
the walls of a house.

Wool clothing – wool is a good insulator
and prevents us from losing body heat.
e
Bunsen
x
Metals
Examples of radiation:
Solar energy
Energy from the sun travels through space to
the earth by radiation. There is no medium
just a vacuum.
Dy
Wooden
ring




Set up the apparatus as shown.
A thumbtack is attached with wax
to each of four metal strips with
wax.
A Bunsen flame is placed at ‘x’ and
the four strips are heated evenly.
The thumbtack which falls first
indicates the best conductor.



Heat the water as shown.
The hot water rises as a convection
current and the dye goes with it.
The dye makes the current visible.
Mandatory experiment: To show convection in a
gas
Smoke
Mandatory experiment: To show that water is a
poor conductor.




Fill a test tube with water.
Hold the test tube at the bottom
and heat the mouth with a Bunsen
burner.
The water at the mouth of the
test tube will be boiling but you
will still be able to hold the
bottom of the tube.
This is because the water is a
poor conductor.
Candle
Box with glass front



The candle creates an updraft
(convection current) of hot air.
The hot air rises and leaves through
the chimney on the left.
Cold air is drawn in from outside,
through the chimney on the right, to
replace it.
Mandatory experiment: To show heat transfer
by radiation
Mandatory experiment: To show that liquids
expand when heated
Thermometer 2
Flask
filled
with
Heat


Candle



Thermometer 1
Place two thermometers equal
distances from a candle, as shown
above.
Thermometer 1 shows a small
increase in temperature. This is due
to radiated heat only.
Thermometer 2 shows a large
increase in temperature. This due to
radiated heat and convection.
Solids, liquids and gases expand when they are
heated. The following experiments are used to
demonstrate this fact.
Mandatory experiment: To show that solids
expand when heated.

Put the ball through the hoop, to
check that it fits through the hoop.

Heat the ball for 30 seconds with a
Bunsen burner.

Try to fit the ball through now.

It cannot be done.

water
Heat the flask as shown.
Since the flask is already full, any
expansion of the water will be seen
as the water rises up the tube.
The water level in the tube will fall
if the flask is cooled.
Mandatory experiment: To show that gases
expand when heated

Heat the flask as shown.

The air in the flask will expand.

The expanded air has only one
escape route, out through the top of
the tube.

If the tube is held under the water,
the expanded air can be seen
bubbling out.

If the flask is allowed to cool, the
air in the flask will contract and
water will be sucked into the flask.
Heat the flask