Energy transfer through different mediums can be
explained using wave and particle models.
• As we go through this topic we will learn
about conduction, radiation, convection,
wave features, sound waves, electromagnetic
waves and spectrum, how waves interact
through absorption, refraction and reflection.
• We will learn their processes and how they are
relevant to everyday situations which are the
examples.
By Cassandra Sweetman
FIRST WE WILL LOOK AT
PARTICLE INTERACTION
SOLID
LIQUID
GAS
Solid
In a solid, the particles are closely packed together.
They vibrate on the spot but keep the shape of the
substance.
Liquid
In a liquid, particles are packed
closely together too. They vibrate but
are free to move or flow over and
round each other.
GAS
In a gas, the particles are not bound together
at all and a are free to move in straight
lines until they collide with another particle
or the walls of the container.
Heating Substances
• When you heat a substance you are adding energy
to its particles. Some of the energy is stored in the
material itself as potential energy. The leftover heat
energy increases the kinetic energy of the particles
in the material. Kinetic energy is the energy of
movement.
• So if you increase the temperature of a substance,
then its particles move faster and faster causing it to
expand. Similarly, if you decrease the temperature of
a substance the particles lose kinetic energy and this
causes the substance to contract.
HEATING SUBSTANCES
• When sufficient heat energy is added to a solid or a
liquid. The particles separate, they break free of the
bonds that join them and so the substance changes
state.
Gas state
Solid
state
Liquid
state
HEAT TRANSFER
The transfer of thermal energy between matter due to a
difference in their temperatures. Heat transfer can happen
in 3 ways! CONVECTION, CONDUCTION AND
RADIATION…
CONDUCTION
Is the transfer of energy through direct contact.
This can be seen in everyday situations such as:
• Touching a metal spoon that is sitting in a pot of
boiling water. The heat is moving up the spoon handle
from the water.
• Holding an ice cube in your
hand makes your hand get
cold. This is because the heat
flows from your skin into the
ice, lowering the temperature
of your skin in the process.
The ice cube is absorbing this
heat because it starts to melt.
CONVECTION
Is the transfer of heat from one place to another by
the movement of fluids.
This can be seen in everyday objects such as:
•Hot air corn popper - The hot air moves against the
corn kernels causing them to get hot enough to pop.
•Boiling water - The heat
passes from the burner into the
pot, heating the water at the
bottom. Then, this hot water
rises and cooler water moves
down to replace it, causing a
circular motion.
RADIATION
Is the emission of energy as electromagnetic waves.
• Objects such as microwaves, lasers, radio waves,
mobiles, computer screens and even the sun produce
radiation.
The underlying rules in these three
heat transfer processes is:
• That heat flows from high-temperature situations
into lower-temperature situations.
• In radiation: electromagnetic waves, energy is
transferred through vibrations of electric and
magnetic fields.
• In convection: water waves, energy is transferred
through the vibration of the water particles.
• In conduction: direct contact, energy is transferred
through the vibration of the material particles
WAVES
WHAT IS A WAVE?
• A WAVE is an energy vibration that usually
takes place in matter
• Key word: vibration. waves repeat!!
• A single “wave” is called a pulse
FEATURES OF A WAVE
We use four different
characteristics to talk about
waves: wavelength, amplitude,
period, frequency.
• Wavelength is the distance between identical parts of
a wave (crestcrest, troughtrough.
• Amplitude is half the wave’s total height, or the
distance between the crest and the rest position.
• Period is the time it takes for one vibration to occur.
FREQUENCY
• A wave’s frequency tells us how often waves
occur (2 waves a second, 4 waves a second, etc)
 The units of frequency are hertz, or hz
 1 hz = 1 wave/second
 Frequency = 1/period
SPEED OF A WAVE
• A waves speed is how fast a wave is moving… to
calculate this we can use either of these equations:
WAVE’S SPEED = WAVELENGTH/TIME
(M/S)
(M)
(S)
OR
WAVE’S SPEED = FREQUENCY X WAVELENGTH
(M/S)
(HZ)
(M)
A handy hint to help you
remember the equations
WAVE TYPES
Transverse waves vibrate at a right angles to the
disturbance or vibration (direction of motion).
Examples: light, ocean waves, waves on a rope
Longitudinal waves vibrate along in the same
direction as the disturbance or vibration (direction
of motion).
Examples: sound, p-waves, “slinky” waves
SOUND WAVES
• In sound waves, energy is transferred through
vibration of air particles or particles of a solid
through which the sound travels.
• For example a drum skin is struck,
it vibrates which causes the air
beside the drum to vibrate.
• The compression and stretching of
air particles creates a sound wave
which is carried through the air to
your ear.
What type of wave is a sound
wave???????
SOUND AND STATES OF MATTER
Sound waves need a substance to travel through.
What are all substances made of? particles
solid
liquid
gas
What is the particle model of a solid, a liquid and a gas?
In which state are the particles closest together?
In which state are the particles furthest apart?
solid
gas
Sound waves travel by particles vibrating.
What state does sound travel fastest through and why?
solid
liquid
gas
Sound waves travel fastest through solids.
The particles in a solid are closer together than in a gas or
a liquid. This means vibrations are more easily and quickly
passed from one particle to the next particle and so sound
waves travels faster.
SPEED OF SOUND – EXPERIMENT
This investigation to calculate the speed of sound should
be carried out in a quiet open space.
100 m
1. When you see the hands clap, press. START.
2. When you hear the hands clap, press STOP.
RESULTS
Record the results of the sound experiment:
Experiment
1
Distance (m)
100
Time (s)
Speed (m/s)
0.34
294
2
3
4
How are these values used to estimate the speed of sound?
Distance (m)
Speed (m/s)=
100 m
=
Time (s)
=
0.34s
294 m/s
ANALYSIS
The first experiment gives an estimate for the speed of sound as 294 m/s.
Use the mean of our results to calculate another estimate for the speed of
sound for your experiment.
1. How does this calculation for the mean speed of
sound compare with the real speed?
2. What errors could have affected the results of the
clapping experiment?
3. Do you think the speed of sound in water is the
same as the speed of sound in air?
SOUND OR LIGHT
WHICH IS FASTER?
Your in a thunderstorm, thunder
and lightning are commencing.
Which do you notice first if their
both created at the same time?
Usually, you see lightning
before you hear thunder .
Light travels much faster
than sound.
The speed of light is… 300,000,000 m/s
How much faster is light than sound?
How could you use thunder and the speed of sound
to estimate how far away a thunderstorm is?
Breaking the sound barrier!
Which of these travel faster than the speed of sound in air?
distance
(m)
time
(s)
speed
(m/s)
small
aeroplane
600
5
120
jet fighter
900
2
450
cheetah
50
2.5
20
meteorite
10 000
0.35
28 571
The jet fighter and the meteorite break the
sound barrier. What does this mean?
Reflected sound waves
What happens when a sound wave meets a
hard flat surface?
The sound wave is reflected back from the surface.
What type of sound does this create?
echo
ECHOES AND REFLECTION
Are hard or soft surfaces best at reflecting sound?
Hard surfaces produce stronger
echoes then soft surfaces.
How are echoes reduced in cinemas and theatres?
By using soft materials on the walls such as curtains
to quieten the outside disturbance.
Name two animals that use echoes for navigation or
communication.
bats and dolphins
STUDYING SOUND WAVES
Sound waves can be studied with this type of equipment.
loudspeaker
oscilloscope
signal generator
Which piece of equipment:
 produces signals over a range of
signal generator
frequencies and of varying amplitudes?
 converts signals into sound waves?
loudspeaker
 is used to study the frequency and
loudness of a sound?
oscilloscope
LOUDNESS AND AMPLITUDE
A sound can be quiet or loud.
Quiet sound
Loud sound
On an oscilloscope trace, the loudness of a sound is
shown by the height of the wave (amplitude).
The larger the amplitude of the wave on the
trace, the louder/quieter the sound.
PITCH AND FREQUENCY
A sound can be high or low – this is the pitch of the sound.
low pitch
high pitch
On an oscilloscope trace, the pitch of a sound is shown
by how many waves there are (frequency).
The greater the number of waves across
the oscilloscope trace, the lower/higher
the frequency and pitch.
WHICH IS THE LOUDEST AND
HIGHEST?
Which trace represents the loudest sound?
A
B
Sound A has the largest
amplitude (i.e. the
tallest waves), so it is
the loudest of these two
sounds.
Which trace represents the sound with the highest pitch?
A
B
Sound B has the greater
number of waves across
the oscilloscope – it has
the highest frequency
and so has the highest
pitch.
A WAVE
ANIMATION
HOW DOES THE EAR HEAR?
1.Sound waves are
collected by the
ear lobe or
pinna. 1
4
2
2.The waves
travel along
the ear canal.
3.The waves
make the ear
drum vibrate.
3
6.The auditory nerve
takes the signals
to the brain.
6
5
5.The cochlea
turns these
into electrical
4.The small bones
signals.
(ossicles) amplify
the vibrations.
HOW DOES THE EAR HEAR?
Can we hear all frequencies?
Set the volume and increase the frequency of the signal
provided by the signal generator.
Humans cannot hear sounds of every frequency.
The range of frequencies you can hear is called your
hearing range.
What is the hearing range of a healthy young person?
20 Hz to 20,000 Hz
Do all animals have the same hearing
range?
100,000
10,000
1,000
frequency
(Hz)
100
10
1
0
human
dog
bat elephant mouse dolphin
HOW IS LOUDNESS MEASURED?
The loudness of a sound is measured in decibels (dB).
0 dB = quietest audible sound (almost total silence)
10 dB = 10 times more powerful than the quietest sound
20 dB = 100 times more powerful than the quietest sound
How much more powerful than the quietest sound is 30 dB?
1,000 times
A whisper is 30 dB and normal conversation is 60 dB.
How much more powerful is normal conversation compared
to a whisper?
1,000 times
HOW LOUD IS LOUD?
decibels
aircraft
overhead
160
personal stereo
140
permanent
ear damage
120
100
loud
bell
80
quiet
countryside
60
40
pin being
dropped
circular saw
at 2m
20
0
can just
be heard
WHAT IS
ULTRASOUND?
The upper frequency limit of human hearing 20,000 Hz.
Any high frequency sound above 20 kHz is called…
an ULTRASOUND
For example:
Whales and dolphins communicate using ultrasound.
Why does a dog whistle vibrate at ultrasound frequencies?
Can you name another human use of ultrasound?
USING ULTRASOUND
Which of the following does not use ultrasound?
imaging foetuses
dolphins
jewellery cleaning
ultrasonic toothbrush
viewing kidney stones
bats
ultrasonic cleaning
echo location
submarines
It’s a trick question! All of the above involve ultrasound.
High frequencies can be very useful!
4 Ways that waves interact
Reflection, Refraction, Transmission
and Absorption
1. Reflection: When a wave hits
a surface through which it cannot
pass, it bounces back.
2. Refraction: Is the
bending of a wave as it
moves from one medium
into another medium at an
angle, it changes speed as it
enters the second medium,
which causes it to bend.
3. Transmission
• Occurs when waves pass through a given point or medium.
Example: sound waves transmitted through solids,
liquids and gases. Radio waves are transmitted through
one electron through another.
• Light waves are transmitted – 3 ways light and matter
can pass through material.
3 ways light and matter can
pass through material.
A. Transparent material: only a small amount of light is
reflected or absorbed (may be clear or colored material
such as filters, windows).
B. Opaque material: allows no light waves to be
transmitted through them.
C. Translucent materials: transmit some light, but cause
it to be scattered so no clear image is seen.
4. ABSORPTION
• Occurs when the energy is not transferred through or
reflected by the given medium
• Disappearance of an electromagnetic wave into a
medium.
• Opposite of reflection
• We see colors because of the selective absorption of visible
light.
• Objects absorb certain wavelengths and we see what
is leftover.
• The colors we see depend on the wavelength absorbed.
Example of Absorption
Yellow
Orange
Green
Red
Blue
Red
Violet
The apple absorbs all
wavelengths except red.
The apple reflects mostly
red. Therefore, it looks
like red.
ABSORPTION
• A material that absorbs all wavelengths of visible light
will appear black.
• In contrast, a material that reflects all wavelengths will
appear white.
• Objects or substances that absorb any wavelength of em
radiation become warmer and convert the absorbed
energy to infrared radiation. (Greenhouse effect)
1. WHAT ARE THE 4 WAYS WAVES WILL
INTERACT? Reflection, Refraction,Transmission and
Absorption
2. WHAT ARE THE 3 WAYS LIGHT AND MATTER CAN
PASS THROUGH? Transparent
Opaque
Translucent
3. WHAT IS THE COLOR WHITE AND THE COLOR
White is all color reflected
BLACK?
Black is all color absorbed
INTERFERENCE OF WAVES
• When two or more waves are moving through a medium at the
same time.
• Constructive interference – when two waves combine to make a
wave with larger amplitude.
• “Helping each other”
• Destructive interference – when the amplitude of two waves
combine with each other producing a smaller amplitude.
ELECTROMAGNETIC WAVES
• EM waves are transverse waves that have some
electrical properties and some magnetic properties.
• It consists of changing electric and magnetic fields
where waves travel as vibrations
• EM waves vary based on wavelength, energy and
frequency.
• Electromagnetic energy is created by vibrations
(just like mechanical waves).
• Each EM wave emits at different energy levels.
• The collection of all EM frequencies is known as the
“Electromagnetic Spectrum”.
EM (ELECTROMAGNETIC WAVES)
• HOW DO ELECTROMAGNETIC WAVES DIFFER
FROM MECHANICAL WAVES????
• EM WAVES DO NOT NEED A MEDIUM TO
TRAVEL THROUGH.
ELECTROMAGNETIC
SPECTRUM
ELECTROMAGNETIC SPECTRUM
1.
RADIO WAVES ARE USED TO TRANSMIT RADIO
AND TELEVISION SIGNALS. RADIO WAVES HAVE
WAVELENGTHS THAT RANGE FROM LESS THAN
A CENTIMETER TO TENS OR EVEN HUNDREDS OF
METERS.
• LONGEST WAVELENGTH, LOWEST
FREQUENCY AND LEAST AMOUNT OF
ENERGY.
• THEY TRAVEL LONG DISTANCES BY
REFLECTING THEIR SIGNALS OFF EARTH’S
ATMOSPHERE OR OFF SATELLITES.
2. MICROWAVES – SHORTER WAVELENGTHS,
HIGHER FREQUENCIES, AND MORE ENERGY
THAN RADIO WAVES.
• CELL PHONES AND RADAR ARE TWO USES
OF MICROWAVES.
3. INFRARED LIGHT - IS THE REGION OF THE
ELECTROMAGNETIC SPECTRUM THAT EXTENDS
FROM THE VISIBLE REGION TO ABOUT ONE
MILLIMETER (IN WAVELENGTH). INFRARED
WAVES INCLUDE THERMAL RADIATION.
ELECTROMAGNETIC SPECTRUM
4.
VISIBLE LIGHT – THE RANGE OF EM WAVES
THAT CAN BE DETECTED BY THE HUMAN EYE.
• LONGEST WAVELENGTH IS OF VISIBLE
LIGHT IS RED.
• SHORTEST WAVELENGTH OF VISIBLE LIGHT
IS VIOLET.
• THE COLOR WE SEE IS DETERMINED BY THE
WAY THE LIGHT INTERACTS WITH THE OBJECT.
• HOW IT IS REFLECTED AND HOW IT IS
TRANSMITTED.
• 400 – 700 NM (NANOMETERS)
Visible Light
Each of these colors actually corresponds to
a different wavelength of light.
How Roy G. Bv Lost a Vowel
The sequence of colors red, orange, yellow, green, blue, and violet may be
remembered by memorizing the name of that fine fellow "ROY G. BV". This was
originally "ROY G. BIV", because it used to be common to call the region between
blue and violet "indigo". In modern usage, indigo is not usually distinguished as a
separate color in the visible spectrum; thus Roy no longer has any vowels in his
last name.
5. Ultraviolet light (UV)- higher frequency than visible
light and carry more energy.
• Can damage or kill living cells
• Tan skin by the sun or tanning bed
6. X-rays - high energy waves which have great
penetrating power and are used extensively in medical
applications and in inspecting welds. The wavelength
range is from about ten billionths of a meter to about
10 trillionths of a meter.
• Short wavelengths and high frequencies allow them
to travel through skin, but not bone (more dense)
7.
Gamma rays – shortest waves, with the highest
frequency (and highest energy).
• They are more penetrating than x-rays
• Can kill living cells
• Used to sterilize medical equipment
HOW DO PRISMS SEPARATE
VISIBLE LIGHT?
• When light shines through a prism, the glass changes the
behavior of each light wave according to the wave's wavelength.
• This property of glass is known as its refractive index.
• The prism changes the direction the light is traveling.
• As a result, what goes in as ordinary white light comes out
separated into a spectrum of different colors.
• That's because white light is really all those wavelengths
mixed together.
Visible Light
Each of these colors actually corresponds to
a different wavelength of light.
TOPIC TEST
• BRING PENCILS, PENS, RULER, RUBBER
AND CALCULATOR
• TAKES 50MINS
• OUT OF 50 MARKS