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Physics
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Static Electricity
Current Electricity
When some materials are rubbed together they
become charged.
Electric current is the flow of charged particles (electrons) through a circuit.
• Friction between the two materials causes
electrons to be removed from one of them
and added to the other.
• When a material gains electrons it becomes
negatively charged.
• The material that loses electrons becomes
positively charged.
• If the material is an insulator, these charges
remain at the point they are produced.
• This is then called static electricity.
Electric charges can move through some materials:
• materials that are electrical conductors will allow
charges to flow away from the point where they start
• good conductors e.g. metals, will allow charges to
move through them freely.
• the flow of charged particles through the conductors
in a circuit is known as an electric current.
• for an electric current to flow we need a power
supply and a complete circuit.
Examples of static electricity in action
ELECTRICITY & MAGNETISM
Circuits - Current & Voltage
The electric current that flows around an electric
circuit is a flow of charged particles called electrons:
• the electrons transfer energy from the power supply
to the components in the circuit.
• the current is measured in units called amps (A) and
can be measured using a device called an ammeter,
placed in series with components.
• the current that leaves a component is the same as
the current that enters it.
• the current is not used up by the components in the
circuit - they use the energy carried by the current.
• we follow the convention that current flows from the
positive terminal of the power supply to the negative
end (although electrons, being negatively charged,
actually move the other way).
+
Charged objects interact with each other:
Voltage (Potential Difference)
+
+
+ -
LIKE charges REPEL
UNLIKE charges ATTRACT
Conventional current flow
Movement of electrons
Voltage is the electrical ʻpushʼ given to the charges (electrons) in the circuit.
The voltage represents a difference in electrical energy between two points in a circuit:
•
•
•
•
•
the bigger the difference in energy, the bigger the voltage.
voltage is also known as potential difference (p.d.).
voltage is measured in units called volts (V).
voltage can be measured using a device called a voltmeter.
to measure the voltage across a component in a circuit, you must connect a voltmeter in
parallel with it.
• you can measure the voltage across a cell or battery - the more cells, the bigger the
voltage (as long as they are connected the right way round).
• the cell or power supply transfers energy to the charges, and pushes them through the
wires and components. If you take the cell away, the charges are not pushed through the
circuit any more and the components do not work. If you add more cells, more energy is
transferred to the charges.
Series Circuits
Parallel Circuits
(Arrows show direction of current flow)
Features of a Series circuit
(Arrows show direction of current flow)
Features of a Parallel circuit
• There is only one current path between the power
supply terminals.
• A switch placed anywhere in the circuit will affect all
of the components in the circuit.
• The current is the same at all points in the circuit.
• The current flowing in the circuit depends on the
power supply and the number and type of
components in the circuit.
• Increasing the voltage of the power supply will
increase the current.
• Adding more components will reduce the current, as
there will then be more resistance in the circuit.
• If a component in the circuit breaks then the circuit
will cease to work, as there is only one current path
and therefore no longer a complete circuit.
ELECTRICITY & MAGNETISM
Circuits - Types of Circuits
AND/OR Circuits and Truth Tables
AND Circuit
• There is more than one current path between the
terminals of the power supply.
• A switch will only affect the components in the same
current path.
• The current splits at a junction in the circuit and rejoins
when the branches meet again.
• The current is not the same at all points in the circuit.
• The current in each branch of the circuit depends on
the components in that branch.
• If a component in one branch of the circuit breaks it
will not affect the other branches, as they are separate
current paths and so they still form a complete circuit.
• Each branch of the circuit gets the full ʻpushʼ from the
power supply voltage.
OR Circuit
Switch A
Switch B
Lamp
Switch A
Switch B
Lamp
Open
Open
Off
Open
Open
Off
Closed
Open
Off
Closed
Open
On
Open
Closed
Off
Open
Closed
On
Closed
Closed
On
Closed
Closed
On
Lamp is on when Switch A AND Switch B are closed
Lamp is on when Switch A OR Switch B are closed
Building Basic Circuits
Using this idea, and assuming that all cells and lamps are the same, look at the following circuits....
In this circuit, when the switch is closed,
we say that the lamp lights to normal
brightness - one cell is supplying energy
to one lamp.
Complete Circuits
When building any kind of circuit it is vital
that the circuit is complete - this means
that the circuit contains an appropriate
power supply and all of the necessary
components (lamps, motors, buzzers
etc.), connected together by wires without
any breaks in the circuit. Any gaps in the
circuit will prevent current from flowing.
Circuit Symbols
ELECTRICITY & MAGNETISM
Circuits - Constructing Circuits
When designing circuits on paper we use
circuit symbols to represent components,
rather than draw out a full picture of each
component. The symbols make it easy to
map out circuits and to understand how
they work. It is important to know a range
of circuit symbols for your physics exam.
Short Circuits
In this circuit the buzzer should
sound and the lamp should light
to normal brightness, as the
circuit is complete and the current
flows through both components.
If we now connect an extra piece of
wire around the lamp as shown, the
buzzer will sound but the lamp will no
longer light. This is because the
current will take the route with least
resistance - the new piece of wire with
no component.
We call this a short circuit.
In this circuit, the motor is being
short-circuited by the wire running
diagonally from the top-left to
bottom-right of the circuit. The motor
will therefore not work as the current
flows along this wire.
In this circuit an extra parallel branch
has been included (often a mistake
made by pupils when drawing
parallel circuits). The extra branch
actually creates a short circuit and
none of the lamps light up.
Measuring Current
Measuring Voltage
In order to measure voltage across a component we
have to:
In order to measure current we have to:
An analogue
ammeter
• use a device called an ammeter
• connect the ammeter in series with the circuit components
• remember that in a series circuit the current will be the
same at all points in the circuit
• remember that in a parallel circuit the current splits up at a
junction and re-combines when the branches join up
again
• remember that current is measured in amps.
Symbol for an ammeter is
A
• use a device called a voltmeter
• connect the voltmeter in parallel with the
component
• remember that voltage is measured in volts.
Symbol for a voltmeter is
V
An analogue
voltmeter
ELECTRICITY & MAGNETISM
Circuits - Measuring
Current & Voltage
Voltmeter is placed in parallel
with the component - this shows
the voltage across the
component
Series: Current the same at all
points in the circuit
A1=A2=A3
Energy Transfers in Circuits
Several energy transfers take place in electrical circuits:
Digital Multimeters
Although you may often use analogue
ammeters and voltmeters to measure
current and voltage in the school
laboratory, digital multimeters can do the
job of both when connected correctly in
the circuit. They can be used to measure
resistance too.
Parallel: Current entering junction is the
same as current leaving the junction
A1=A4
Current splits at the junction and recombines
afterwards i.e. A1=A2+A3 and A2+A3=A4
•
•
A cell or a battery is a store of chemical energy
In a complete circuit, this chemical energy is converted
into electrical energy, which is moved around the circuit
by the current.
• In this way the energy is transferred to other devices in
the circuit.
• The other devices in the circuit change the electrical
energy into different forms.
e.g. lamp transfers electrical energy into light energy, buzzer
transfers electrical energy into sound energy etc.
Poles of a Magnet
When a piece of magnetic material (e.g. iron, steel,
cobalt, nickel) is magnetised we call it a magnet.
• All magnets have two poles, the north-seeking
pole (north pole for short) and the south-seeking
pole (south pole for short).
• Every magnet has a space around it where it
exerts a force on other magnets or other magnetic
materials.
• The poles are where the magnetic force is
strongest.
• Magnets exert forces on other magnets - opposite
magnetic poles exert a force of attraction on each
other; similar magnetic poles exert a force of
repulsion on each other.
The Field Around a Bar Magnet
The Magnetic field around a bar magnet can be
described by field lines as shown on the diagram
below:
The field pattern is
out of the North and
into the South
The field around a bar magnet can be
investigated using a plotting compass to track
the field lines as shown below:
The field is strongest
at the poles where
the field lines are
most concentrated
ELECTRICITY & MAGNETISM
Magnetic Fields
The field pattern can also be viewed using iron
filings. When iron filings are sprinkled onto a
sheet of card above a bar magnet, the filings
line up in the pattern of the magnetic field:
The Earthʼs Magnetic Field
Remember: LIKE POLES REPEL, UNLIKE POLES
ATTRACT
Also be aware that repulsion is the only true test for a
magnet - you can only show that an object is a
magnet if it repels a known magnet.
Permanent Magnets
Bar magnets are permanent magnets.
This means that their magnetism is there
all the time and cannot be turned on or
off.
The Earth has a magnetic north pole and a magnetic
south pole. It behaves as though it has a giant bar
magnet inside it. Bar magnets can line up in the
Earth's magnetic field and point north - this is what
allows a compass to work.
Remember that the north pole of a bar magnet is
actually called the 'north-seeking pole', and it points to
the Earth's magnetic north pole, while the ʻsouthseeking poleʼ points to the Earthʼs magnetic south
pole.
Magnetic Fields Due to Current Carrying Wires
The Field Produced by a Coil
When an electric current flows there is a magnetic field associated
with it and this can be demonstrated using the setup shown below.
When the circuit is switched on, the current flows through the wire
and iron filings or plotting compasses placed on the cardboard around
the wire line up, in the pattern of the magnetic field caused by the
current. It is a pattern of concentric circles around the wire.
When a coil of wire (solenoid) is
connected to a power supply and a
current passed through it, the
magnetic field pattern produced is the
same as that of a bar magnet. If
plotting compasses are used to
investigate the field pattern the
familiar arrangement of field lines
running out of the north and into the
south is produced. If the power supply
is reversed though, the field pattern is
also reversed.
Power
Supply
+
Power
Supply
Switch
ELECTRICITY & MAGNETISM
Electromagnets
There are a number of uses of electromagnets. They are
found in loudspeakers, relays, electric motors, lifting
magnets in scrapyards, electric bells etc.
Examining how the electric bell works in useful in
understanding the uses of electromagnets:
Hammer
Constructing an Electromagnet
A magnetic field is produced when an
electric current flows through a coil of wire.
This is the basis of the electromagnet. Unlike
bar magnets, which are permanent magnets,
the magnetism of electromagnets can be
turned on and off just by turning the power
supply on or off.
Uses of Electromagnets
Gong
The strength of an electromagnet can be increased in Electromagnet
three ways:
1) Adding more turns to the coil of wire
2) Increasing the current through the coil
3) Wrapping the coil around an iron core
A simple electromagnet can be made by winding wire
around a nail very tightly. The more windings, the
stronger the magnet, but the ends should be left free.
There should be only one layer of wire on the nail.
The ends of wire are then connected to a battery.
Now paper clips, staples, and even other nails can be
picked up. When the battery is disconnected, the
electromagnet is turned off. The nail may still be a bit
magnetized, but it will soon wear off. If the
electromagnet is left on for too long; it will quickly get
hot and drain the battery.
Sprung
metal arm
When the switch is pressed, the circuit is complete
and the current flows through the electromagnet
setting up a magnetic field, which attracts the metal
arm towards it. This causes the hammer to hit the
gong but breaks the circuit, cutting off the current and
switching off the electromagnet The arm then springs
back to its original position which completes the circuit
again. This process continues until the switch is
released.
Types of Force & their Effects
Speed and its Measurement
Balanced & Unbalanced Forces
• Forces are just pushes and pulls
• You canʼt see a force but you can see the effects of
a force.
• Forces are measured in Newtons (N).
• Forces usually act in pairs.
• A Newton meter (forcemeter) is used to measure
forces.
To work out the speed of an object, we need
to know:
When two forces acting on an object are equal in size
but act in opposite directions, we say that they are
balanced forces. If the forces on an object are balanced
(or there are no forces acting on it):
• the object stays still, if it is not already moving
• the object continues to move at the same speed and in
the same direction, if it is already moving.
• the distance the object has travelled
• the time taken to travel that distance
The formula for calculating speed is:
ground reaction
force
Five things forces can do to an object:
• Speed it up
• Slow it down
• Change its direction
• Change its shape
• Turn it
Types of force include friction, gravitational force,
reaction force from a surface or the ground
(ground reaction force) or from a liquid (upthrust),
stretching forces, tension and air resistance
(often called drag).
Frictional Forces
Whenever an object moves against another object
or surface, it is likely to experience frictional forces.
These are forces that act in the direction opposite
to the direction of movement of the object
Frictional forces are much smaller on smooth
surfaces than on rough surfaces, which is why we
slide on ice.
Friction can be useful - grip on shoe soles stops
slipping, tread on car tyres helps grip the road,
brakes on vehicles stop the vehicle using friction.
Friction can be a nuisance - when there is a lot of
friction between moving parts, energy is lost to the
surroundings as heat and the parts wear out,
friction slows us down when we want to go faster.
ground reaction
force
The unit of speed in physics is the metre per
second (m/s), as distance is measured in
metres and time is measured in seconds,
although you may have to use kilometres per
hour (km/h) for some problems.
driving
force
of
engine
friction
and air
resistance
weight
weight
Car not moving
(balanced forces)
FORCES & MOTION
Force and Linear Motion
Car moving at
constant speed
(balanced forces)
ground reaction
force
So, to increase friction, we make the surfaces
rougher (e.g. more grip) and to reduce friction we
make the surfaces smoother (e.g. streamlining or
lubrication).
Air Resistance
Air resistance is caused by the frictional forces of
the air against an object travelling though it. The
faster the object (e.g. a vehicle) moves, the bigger
the air resistance becomes. It is often called drag.
air resistance (drag)
weight
When this skydiving sheepʼs air
resistance & weight are balanced, his
speed remains constant (terminal
velocity). Opening his parachute
increases drag, slowing him down until
he reaches a new terminal velocity,
which is a safe speed for him to land.
driving
force
of
engine
friction
and air
resistance
weight
Car accelerating
(unbalanced forces)
In the last diagram (above), the forces are
unbalanced as the driving force is greater than the
frictional forces, so the car accelerates. If the
frictional forces were greater than the driving force
(by braking for example), the forces would once
again be unbalanced, but this time the car would
slow down (decelerate).
Gravitational Force
Mass and Weight
All objects have a force of attraction between them, that attracts
them towards each other. This force is called gravity. Gravity
only becomes noticeable though when there is a really massive
object involved, like a planet, moon or a star.
The size of the gravitational force depends on the masses of the
objects involved and the distance between them - the greater the
masses and the closer together they are, the bigger the
gravitational force.
The Earth has more mass than the Moon, so the gravitational
force is greater on the Earth than it is on the Moon.
The Earth's gravitational force pulls objects towards the centre of the Earth. This is what gives
objects their weight - weight is the pull of gravity on an objectʼs mass.
Gravity is the force that keeps the Moon in orbit around the Earth and keeps the planets in
orbit around the Sun.
FORCES & MOTION
Gravitational Force &
Stretching
Mass
The mass of an object is the amount of matter it contains.
The more matter an object contains, the greater its mass.
Mass is measured in kilograms (kg) but it is often easier
to measure mass in grams (g). An object's mass stays
the same wherever it is.
Weight
The weight of an object is the result of the gravitational
force between the object and the Earth. The greater the
mass of an object, the greater its weight. Weight is
measured in newtons (N) as it is produced by a force
(gravity).
On Earth, an object with a mass of 1 kg has a weight of
10 N. So, to find the weight of any object in Newtons, we
multiply its mass by 10.
Remember that the mass of an object stays the same
wherever it is, but the weight of the same object can
change. This happens if the object goes somewhere
where gravity is stronger or weaker, such as into space.
i.e. a person with a mass of 60 kg will have a weight of
600 N on Earth - in space the personʼs mass will still be
60 kg, but their weight will be 0 N (zero gravity in space);
on the Moon the personʼs mass will still be 60 kg but their
weight will be 100 N as the Moon has one sixth of the
Earthʼs gravity.
Stretching Objects
Some objects can be stretched or compressed when a
force is applied to them (e.g. hanging a weight from a
spring). Bodies which are able to change shape when a
force is exerted on them and return to their original
shape when the force is removed are said to be elastic.
When a single spring has a
weight (load) hung from it, the
extension of the spring is
proportional to the load applied.
i.e. the greater the load the
greater the extension
When two springs are connected in
parallel, they share the load and so
the extension is half of that of a
single spring with the same weight
applied.
Stretching Springs
A spring with no weight attached
will have a particular length
(original length) if it has not been
deformed (stretched beyond its
limit of proportionality).
When two springs are connected in
series, the extension produced is still
proportional to the load, but each
spring stretches as much as one on
its own, so the extension is doubled.
Remember, in each case:
Extension = New length - Original length
For Springs in Series:
Total Extension = Extension of one spring x N
For Springs in Parallel:
Total Extension = Extension of one spring ÷ N
(Where N is number of springs)
Levers and Simple Machines
Simple machines make work easier for us by allowing us to push or pull over increased distances. Here are some examples of simple machines:
Pulley
A pulley is a simple
machine that uses grooved
wheels and a rope to raise,
lower or move a load.
Lever
A lever is a stiff bar that
rests on a support called a
fulcrum which lifts or moves
loads.
Wedge
A wedge is an object with
at least one slanting side
ending in a sharp edge,
which cuts material apart.
Wheel & Axle
A wheel with a rod, called
an axle, through its center
lifts or moves loads.
Screw
A screw is an inclined
plane wrapped around a
pole which holds things
together or lifts materials.
In the above examples, each machine makes work
easier to do by providing some trade-off between the
force applied and the distance over which the force is
applied.
Moments
Forces can make objects turn if there is a pivot. The
moment of a force is a measure of the turning effect (or
torque) produced by a force acting on an object.
Example: Think of a see-saw. When no-one is on it the seesaw is level, but it tips up if someone gets onto one end. It is
possible to balance the see-saw again if someone else gets
onto the other end and sits in the correct place. This is all
due to moments.
To work out a moment, we need to know:
• the force or load applied
• the distance from the pivot that the force or load is applied
Inclined Plane
An inclined plane is a
slanting surface
connecting a lower level
to a higher level.
FORCES & MOTION
Force and Rotation
Example 1
In the example below, a see-saw has been
set up and a 4 Newton load has been
placed 0.4 metres from the pivot:
Example 2
In the example below, a see-saw has been set up and a
5 Newton load has been placed 0.5 metres from the
pivot. This time we need to work out the size of the force
required to balance the see-saw, when placed 0.25 m
away from the pivot, on the other side:
The general formula for working out moments is:
moment = force x distance
(Remember that the distance in this formula is the distance
of the force from the pivot.) The unit of moment is Nm
(newton metre).
Using the formula for moments:
moment = force x distance
it is clear that the moment (or turning
effect) on this see-saw is...
moment = 4 x 0.4 = 1.6 Nm
To work this out we need to consider the moments on
each side of the pivot. When moments work in opposite
turning directions, we often refer to them as clockwise
and anti-clockwise moments. So...
Clockwise moments = F x d = 5 x 0.5 = 2.5 Nm
Anti-clockwise moments = F x d = F x 0.25
For the see-saw to balance, the clockwise and anticlockwise moments must be equal. Therefore...
F x 0.25 = 2.5
and so... F = 2.5/0.25 = 5 N
Relationship between Force, Pressure and Area
Pressure is the force acting over a certain
area. The formula for pressure is:
Pressure =
Force
Area
Pressure is measured in units of N/m2
(newton per square metre), but another unit
may also be used. This is called the pascal,
Pa. (1 Pa = 1 N/m2)
Many exam questions also deal with
pressure in N/cm2, usually because a
square metre (m2) is such a large area
to work with when dealing with everyday
situations.
Pressure and its Application
From the formula, it is clear that the greater the area
over which a force acts, the lower the pressure. This
can be seen in a practical situation by considering
the use of a drawing pin:
Drawing pins have a large round end for you to push
the sharp end into a notice board. The round end
applies a low pressure to your thumb, but the sharp
end applies a high pressure to the notice board, so it
pushes in.
Another simple example of how pressure works
can be seen by examining the boxes above. Both
boxes have the same weight (100N), but the first
box lies on one of its sides which has an area of
2m2, causing a pressure of 50 N/m2. The second
box lies on one of its sides which has an area of
1m2, causing a pressure of 100 N/m2. So, although
both boxes have the same weight, the pressure
they cause is different due to the area of their
contact sides.
FORCES & MOTION
Force and Pressure
Force spread over a greater area reduces
pressure...
Pressure in Liquids
Pressure acts in all directions in a liquid but the
deeper you go, the greater the pressure. This is why
dams are wider at their bases than at the top.
Concentrating force over a smaller area
increases pressure...
Hydraulic equipment and machines use the
fact that pressure is transmitted though a
liquid to benefit us. A small force applied at
one point can be used to create a larger
force at another point, due to the hydraulic
pressure within the system e.g. car breaks.
Luminous Sources
Light is produced by luminous objects, such
as fires, electric lamps and stars like the
Sun.
Visible light is a type of radiation and forms a small part of the Electromagnetic Spectrum, which
shows all types of radiation and the wavelengths associated with the different types. Although we
can only see the visible part of the spectrum, we use other types of radiation in various ways,
although some types are dangerous to us.
The light that we can see is called visible
light, but there is also light that we cannot
see, including ultraviolet light and infrared
light.
The Way Light Travels
Light travels very much faster than sound,
which is why you see lightning in a
thunderstorm before you hear the thunder
clap. It travels at 3 x 108 m/s (in other words
300,000,000 m/s).
Light travels in straight lines. It cannot bend
around corners, so we cannot see around a
corner unless we use a mirror. We
get shadows because light cannot
bend round behind an object.
Light cannot travel through opaque
objects, such as brick walls. Opaque
objects can cast dark shadows when
light is shone on them. Light travels
through transparent objects, such as
glass windows. Paper and other
translucent objects let some light
through, but not all of it. This is why
you can see the typing on the other
side of a piece of printed paper if you
hold it up to a light.
LIGHT & SOUND
The Behaviour of Light
- Light & Sight
How We See Objects
We see objects because light reflected from them enters our
eyes. The light from luminous objects such as stars and
lamps may enter our eyes directly. Non-luminous objects do
not make their own light, but we can still see them if light
from a luminous object reflects or scatters off them into our
eyes.
Light reflects off the
non-luminous object
to our eyes, allowing
us to see the object
Light travels from the
light source to the
non-luminous object
Light also travels from
the light source
directly to our eyes
Reflection
Refraction
Light can bounce off surfaces. We call this
reflection and we say that light reflects off
surfaces.
Mirrors are very smooth and shiny. They
reflect light evenly and we can see an image
in them. A flat mirror is called a plane mirror.
Bumpy or rough surfaces do not reflect light
evenly. Instead, the light is scattered in all
directions, and usually we cannot see an
image. This is why you canʼt brush your hair
in front of a brick wall.
There is a rule about how light behaves at plane mirrors:
Angle of incidence = Angle of reflection
LIGHT & SOUND
The Behaviour of Light
- Reflection & Refraction
Dispersion
White light can be split up to form a spectrum by using a prism. A prism is
a triangular block of transparent material like glass or Perspex.
Refraction happens as light enters and leaves a prism. Red light is
refracted the least and violet light is refracted the most. This causes the
different colours in the light to spread out to form a spectrum. Separating
the colours like this is called dispersion. We say that the light has been
dispersed.
The colours in the spectrum are red,
orange, yellow, green, blue, indigo
and violet. It may help to remember
them using ROY G BIV or Richard
Of York Gave Battle In Vain.
Raindrops can disperse sunlight,
which is why we see rainbows.
Light normally travels in straight lines, but it
can bend at the boundary between two
materials with different densities e.g. light
passing from air into a dense glass block will
bend slightly. This is called refraction.
Refraction causes some
interesting effects, such as
making a ruler look like it is
bent when part of it is placed
into a bowl of water and
making ponds look shallower
than they really are.
Colour, Colour Objects and Colour Filters
The three primary colours of light are red, green and blue. If all three are mixed together, we
get white light.
Objects appear white if they can reflect all the colours of the spectrum. Objects appear black
if they absorb all the colours of the spectrum.
Coloured objects reflect some colours and absorb others. For example, a blue cloth reflects
blue light but absorbs the other colours of the spectrum. Shining blue light onto a white object
will make the object look blue, as there is only blue light available to be reflected, whereas a
black object will still look black in
blue light as black objects absorb
all light. Shining blue light onto a
red object will make it look black
as it will only reflect red.
Colour filters work by only letting
one colour of light through and
stopping the other colours.
What is Sound?
Loudness and Amplitude
Pitch and Frequency
Sound is produced whenever an object
vibrates and it transfers energy away from
the vibrating object It needs something to
travel through - sound cannot travel through
a vacuum.
Sound travels at different speeds through
different substances. In general, the denser
the substance, the faster sound travels
through it. Sound travels at 5100 m/s
through steel, 1480 m/s through water and
330 m/s through air. This is much slower
than the speed of light.
When an object vibrates, it causes the
particles of the substance around it (e.g. air)
to vibrate back and forth, which in turn
causes the next particles to vibrate and so
on, forming a wave. This is how sound
travels.
Sound can reflect from the surface of an
object. This is called an echo. Hard surfaces
reflect sound better than soft surfaces.
The loudness of a sound depends upon the amplitude of the
vibrations that cause it. Big vibrations transfer more energy
than small vibrations, so they are louder.
A sound can range from a high to a low pitch.
The pitch of a sound depends upon the
frequency of the vibrations that cause it. The
frequency of a sound is the number of complete
waves or vibrations that go past a particular point
each second.
How We Hear Sounds
We hear because sound waves enter the ear and
cause the eardrum to vibrate. Three small bones
in the inner ear carry these
vibrations to the cochlea. The
cochlea contains tiny hairs, which
send messages to the brain when
they vibrate.
We hear a range of sounds from
low pitch to high pitch. The
range of sound frequencies that
we are able to hear is called the
audible range. This is roughly
between 20 Hz and 20,000 Hz,
b u t d i ff e r e n t p e o p l e h a v e
different audible ranges.
Sound travels as sound waves. The bigger the vibration, the
greater the amplitude of the waves and the louder the sound.
LIGHT & SOUND
Vibration & Sound and
Hearing
Frequency is measured in hertz, with the symbol
Hz. 1 Hz is the equivalent of one wave per
second.
The Effect of Loud Sounds
Our hearing is easily damaged and, as
we get older, our audible range tends to
get smaller. The three small bones may
join together as we age, so they are not
so good at passing along the vibrations
from the ear drum to the cochlea.
Loud sounds, such as those from rock
concerts and using personal audio
players too loudly, can
eventually damage our
hearing. If the ear drum
is damaged, it may
repair itself again, but if
the cochlea is damaged,
the
damage
is
permanent. People with
damaged hearing may
find it difficult to follow
conversations and may
need a hearing aid.
The Variety of Energy Resources
Energy allows things to happen. Energy
cannot be created out of thin air or destroyed
- it can only be stored or transferred from
place to place in different ways.
Energy resources provide us with energy.
There are different types of energy resource,
including fuels such as coal or food, and
stores of energy such as batteries or the
wind. We can divide energy resources into
two categories, non-renewable and
renewable.
Non-Renewable Energy Resources
Non-renewable energy resources cannot be
replaced once they are all used up. Fossil
fuels are examples of non-renewable energy
resources. The fossil fuels are coal, oil and
natural gas. They formed millions of years
ago from the remains of living things. Coal
was formed from plants, and oil and natural
gas from sea creatures. When the living
things died, they were gradually buried by
layers of rock. The buried remains were put
under pressure and chemical reactions
heated them up. They gradually changed
into the fossil fuels.
Temperature, Heat and units of Energy
Temperature and heat are not the same,
although both are concerned with thermal
energy. The temperature of an object is to do
with how hot or cold it is, measured in
degrees Celsius (oC). The heat an object
contains is the amount of its thermal energy,
measured in joules (J). Joules are the units
of Energy.
The Ultimate Source of Energy
Renewable Energy Resources
Renewable energy
resources can be replaced,
and will not run out.
Examples of renewable
energy resources are
biomass fuels (fuels from
living things such as trees),
wind power, water power
(wave machines, tidal
barrages and hydroelectric
power) and solar power.
ENERGY RESOURCES
& ENERGY TRANSFER
Energy Resources
The energy stored in the fossil fuels
originally came from sunlight. Plants used
light energy from the Sun for photosynthesis
to make their chemicals. This stored
chemical energy was transferred to stored
chemical energy in animals that ate the
plants. When the remains of the plants and
animals became fossil fuels, their chemical
energy was stored in the fuels. The energy is
transferred to the surroundings as thermal
energy and light energy when the fuels burn.
Just as with the fossil fuels, the energy
stored in biomass fuels ultimately came from
the Sun.
Wind is caused by huge convection currents
in the Earth's
atmosphere, driven
by heat energy
from the Sun.
This is why the Sun
is regarded as the
ultimate source of
energy - it provides
the energy for all
other resources.
Generating Electricity
Most of the UK's electricity is generated in power
stations using fossil fuels. Thermal energy released
from the burning fuel is used to boil water to make
steam, which expands and turns turbines. These
drive the generators to produce electricity.
As the fossil fuels are non-renewable energy
resources, and they produce pollution when they
burn, we are aiming to produce more of our
electricity using renewable energy resources. This
will reduce the rate at which the fossil fuels are used
up.
Law of Conservation of Energy
Energy cannot be created out of thin air or
destroyed - it can only be stored or transferred
from place to place in different ways. This is
known as the Law of Conservation of Energy.
Forms of Energy and Energy Transfers
Energy can take several forms.
A vibrating drum or a plucked guitar string
transfer energy to the air as sound. This is
sound energy. A moving object is said to have
kinetic energy (movement energy).
A battery transfers stored chemical energy as
electrical energy in the moving charges in the wires.
The electrical energy is transferred to the
surroundings by a lamp as light energy and thermal
energy (heat energy).
Transfer of Heat Energy
Thermal energy can be transferred by:
• conduction
• convection
• radiation
Thermal energy can also be transferred when a liquid
evaporates. The liquid particles with the most energy
leave the liquid and enter the surroundings.
Conduction
Thermal energy can move through a substance by
conduction. When a substance is heated, its particles
gain energy and vibrate more vigorously. The
particles bump into nearby particles and make them
vibrate more. This passes the thermal energy through
the substance by conduction, from the hot end to the
cold end.
Convection
The particles in liquids and gases can move from
place to place. Convection happens when particles
with a lot of thermal energy in a liquid or gas move,
and take the place of particles with less thermal
energy. Thermal energy is transferred from hot
places to cold places by convection.
A rock on the edge of a mountain has stored energy
because of its position above the ground and the pull
of gravity. This energy is called gravitational potential
energy. As the rock falls to the ground, the
gravitational potential energy is transferred as kinetic
energy.
ENERGY RESOURCES
& ENERGY TRANSFER
Conservation of Energy
When an explosive goes off, chemical energy stored
in it is transferred to the surroundings as thermal
energy, sound energy and kinetic energy.
Radiation
All objects transfer thermal energy by radiation called
infrared radiation. The hotter an object is, the more
radiation it gives off. No particles are involved in
radiation, unlike conduction and convection. This
means that thermal energy
transfer by radiation can
even work in space, but
conduction and convection
cannot. Radiation is why
we can feel the heat of the
Sun, even though it is
millions of kilometres away
in space.
Units and Formulae
The following are the important units and formulae you need to know for Common Entrance 13+ exams:
speed =
density =
QUANTITY
UNITS
FORCE
Newtons, N
MASS
kilograms, kg
TIME
seconds, s
WEIGHT
Newtons, N
DISTANCE
metres, m
AREA
square metres, m2 (or cm2)
VOLUME
cubic metres, m3 (or cm3)
PRESSURE
Pascals, Pa (N/m2) (or N/cm2)
DENSITY
kg per m3, kg/m3
SPEED
metres per second, m/s
CURRENT
Amperes, A
POTENTIAL DIFFERENCE
Volts, V
TEMPERATURE
degrees Celsius, C
MOMENT
Newton-metres, Nm
distance
time
mass
volume
d
s
pressure =
t
m
D
force
area
F
P
M
moment = force x distance
V
A
F
d
Circuit Symbols