Transcript Document

18/07/2015
Energy for the Home
(OCR Gateway)
W Richards
The Weald School
P1a – Heating Houses
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Particle theory revision
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Particle theory is all about explaining the properties of solids,
liquids and gases by looking at what the particles do.
SOLIDS
In a solid the particles ______
around a _____ position. There
is a ______ force of attraction
between each particle and they
are very _____ together
Words – strong, close, vibrate, fixed
“Temperature” is simply a way of measuring how fast these
particles are vibrating.
LIQUIDS
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In a liquid the particles are
_____ together but can move in
any direction. They won’t keep a
_____ shape like _____ do.
GASES
In a gas the particles are very
far apart and move _____ in all
directions. They often ______
with each other and because
they are far apart they can be
easily _______.
Words – fixed, collide, quickly, close, squashed, solids
Heat and Temperature
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Heat is a type of energy that will flow from a warm area
to a colder one. For example…
This cup of coffee will ____ ____
because it is _____ ____ heat energy
into the surroundings. The hotter it is,
the quicker this will happen.
This drink (taken out of the fridge)
will _____ ___ because it is _____
___ heat energy from the
surroundings. The colder it is, the
quicker this will happen.
Words – giving out, warm up,
taking in, cool down
Understanding Thermograms
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Specific Heat Capacity
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This can be thought of as “the capacity of an object to store
heat”. Consider some water:
If we heat this beaker up it’s fairly clear
that the amount of energy it gains
depends on how much water there is and
how hot it gets…
Energy α mass x temperature rise
Energy = mass x s.h.c x temp
E = mcΔT
Specific Heat Capacity
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How can we do this experimentally?
E = VIt and E = mcΔT
A
12V
V
Possible errors with this experiment:
1) Temperature throughout the liquid
should be the same
Solution:
2) Heat is lost to the surroundings
Solution(s):
Temp/OC
150
100
Heating ice
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This flat line shows where energy is
being used to push the particles further
apart for evaporation. The amount of
energy needed to turn 1kg of a liquid
into a gas is called the Specific Latent
Heat of Vaporisation L.
50
0
-50
Time/s
This flat line shows where energy is being
used to break bonds – this has to be done
during melting. The amount of energy
needed to turn 1kg of a solid into a liquid is
called the Specific Latent Heat of Fusion L.
Latent Heat of Fusion
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From the previous slide we can say that the energy needed to
melt water is given by…
Energy = mass x specific latent heat of fusion
To work out L
experimentally you could…
VIt = mL
A
12V
V
P1b – Keeping homes warm
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Conduction
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Conduction is all about when heat is transferred through a
_________. The heat is passed on by ___________ in the
molecules. These vibrations get BIGGER when the solid has
more ENERGY (i.e. when it is being __________).
Heating a non-metal
Heating a metal
Metals are _______ conductors than non-metals. This is
because the heat is carried by free ________ that can
carry the energy around the metal and give it to other
electrons and ions.
Words – vibrations, electrons, solid, heated, better
Convection
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Convection is all about when a gas or liquid
(“fluid”) moves and carries heat with it. When
the fluid is heated it ____________. This
means that it will become less __________
than the colder fluid around it. Because of
this the warmer fluid will try to “_______”
over the colder fluid, and this is why warm air
rises. This is called a convection
___________. This is how heat reaches us
from the ___________ in this room.
In CONDUCTION the heat was passed on
by VIBRATIONS in a SOLID
In CONVECTION the heat is passed on by
the FLUID expanding, rising and TAKING
THE HEAT with it
Words to use: expands, radiators, dense, heated, current, float
Some questions on convection…
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1) Freezers in supermarkets are often left open to the
air. Explain why the food does not melt easily.
2) Explain why a hot air balloon rises in the air.
3) Explain why an ice cube floating at the top of a drink
will cool all of the drink.
Radiation
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An introduction…
I’m cool!
I’m very hot!
Some examples of radiation
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“Thermograms”
Some examples of radiation
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Radiation Practical
Time / min
Temperature in each container / 0C
Black
1
2
3
4
5
6
7
8
9
10
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Silver
Clear
Radiation
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Radiation is when heat moves around in electromagnetic _________ like
light does. Any hot object will emit heat radiation – the hotter it is, the
more radiation it emits. This type of radiation is called __________, and
too much of it will cause _________. Dark, matt colours will absorb AND
emit the _____ infra-red radiation, and light, shiny colours will ________
it.
The main difference with radiation is that conduction and convection could
ONLY happen in solids, liquids or gases, whereas radiation will happen
through an _____ _____. This is just as well, as otherwise we wouldn’t be
able to get any heat from the ___.
Words – sun, reflect, infra-red, waves, most, empty space, sunburn
Anything HOT emits HEAT RADIATION – the hotter it
is, the more infra red radiation it emits
Understanding Heat Transfer
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1) Explain how and where all 3 processes
of heat transfer happen in a bonfire
2) By considering how a Thermos
Flask is built explain how it
manages to keep hot drinks hot
and cold drinks cold.
Understanding Heat Transfer 2
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3) Car radiators are
designed to help car
engines lose heat. Explain
how they do this.
4) Some houses have solar collectors on their roof. Explain
how they work:
House insulation
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Loft insulation
Cavity wall
insulation
Double
glazing
Draught excluders
Types of House Insulation
Loft insulation
Double glazing
How do these
forms of
insulation
help?
Cavity wall
insulation
What else
would this
house benefit
from?
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Heat Sources and Heat Sinks
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In general, anything that gives
out heat (e.g. this house) is
called a “heat source”.
The term “heat sink” refers to
the place the source’s heat will
be transferred to, and it’s
usually an object so large that
it’s temperature won’t change.
House insulation
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Type of insulation
Cost
Annual amount
saved
Loft insulation
£400
£80
Double Glazing
£2,000
£50
Cavity wall ins.
£600
£60
Draught excluder
£40
£20
1) Which type of insulation costs the most?
2) Which type of insulation is the most effective?
3) Which type is the most “cost effective”?
4) Which type pays for itself after 40 years?
Efficiency
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Efficiency is a measure of how much USEFUL energy you
get out of an object from the energy you put INTO it.
For example, consider a TV:
Electrical
Energy (200J)
Sound (40J)
Efficiency = Useful energy out
Energy in
x100%
Some examples of efficiency…
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1) 5000J of electrical energy are put into a motor. The
motor converts this into 100J of movement energy. How
efficient is it?
2) A laptop can convert 400J of electrical energy into 240J
of light and sound. What is its efficiency? Where does
the rest of the energy go?
3) A steam engine is 50% efficient. If it delivers 20,000J of
movement energy how much chemical energy was put into
it?
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Energy Transfer (“Sankey”) diagrams
Consider a light bulb. Let’s say that the bulb runs on 100
watts (100 joules per second) and transfers 20 joules per
second into light and the rest into heat. Draw this as a
diagram:
“Input” energy
100 J/s
electrical
energy
“Output” energy
20 J/s
light energy
80 J/s heat
energy (given to
the surroundings)
Example questions
Consider a kettle:
2000 J/s
electrical
energy
Sound
energy
Wasted
heat
Heat to
water
1) Work out each energy value.
2) What is the kettle’s
efficiency?
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Consider a computer:
150 J/s
electrical
energy
10 J/s
wasted
sound
20 J/s
wasted
heat
Useful
light and
sound
1) How much energy is converted
into useful energy?
2) What is the computer’s
efficiency?
P1c A Spectrum of Waves
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An introduction to Waves
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Some definitions…
“Crest”
1) Amplitude – this is
“how high” the wave is:
“Trough”
2) Wavelength () – this is the
distance between two
corresponding points on the
wave and is measured in metres:
3) Frequency – this is how many waves pass by
every second and is measured in Hertz (Hz)
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The Wave Equation
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The wave equation relates the speed of the wave to its
frequency and wavelength:
Wave speed (v) = frequency (f) x wavelength ()
in m/s
in Hz
in m
V
f

Some example wave equation questions
18/07/2015
1) A water wave has a frequency of 2Hz and a wavelength
of 0.3m. How fast is it moving?
0.6m/s
2) A water wave travels through a pond with a speed of
1m/s and a frequency of 5Hz. What is the wavelength
of the waves?
0.2m
3) The speed of sound is 330m/s (in air). When Dave
hears this sound his ear vibrates 660 times a second.
What was the wavelength of the sound?
0.5m
4) Purple light has a wavelength of around 6x10-7m and a
frequency of 5x1014Hz. What is the speed of purple
light?
3x108m/s
Reflection
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Angle of incidence = Angle of reflection
Normal
Reflected ray
Incident ray
Angle of
incidence
Angle of
reflection
Mirror
Refraction through a glass block:
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Wave slows down and bends
towards the normal due to
entering a more dense medium
Wave slows down but is
not bent, due to entering
along the normal
Wave speeds up and bends
away from the normal due to
entering a less dense medium
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Refraction
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Refraction is when waves ____ __ or slow down due to
travelling in a different _________. A medium is
something that waves will travel through. When a pen is
placed in water it looks like this:
In this case the light rays are slowed down by the water
and are _____, causing the pen to look odd. The two
mediums in this example are ______ and _______.
Words – speed up, water, air, bent, medium
Wave diagrams
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1) Reflection
2) Refraction
3) Refraction
4) Diffraction
Diffraction
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More diffraction if the size of the gap is similar to the wavelength
More diffraction if wavelength is increased (or frequency decreased)
Limiting Effects of Diffraction
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The effect of diffraction causes microscopes and telescopes
to naturally have a limit of what they can “resolve”.
This is the image seen by a telescope when pointing at a star –
the rings are caused by diffraction effects and they will cause
difficulty when viewing stars that are near each other.
Electromagnetic Radiation
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E-M radiation is basically a movement of energy in the form of
a wave. Some examples:
The Electromagnetic Spectrum
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Each type of radiation shown in the electromagnetic spectrum has a
different wavelength and a different frequency:
High frequency,
_____ wavelength
Gamma
rays
X-rays
Low frequency, _____
(high) wavelength
Ultra violet
Visible
light
Infra red
Microwaves
Radio/TV
γ
Each of these types travels at the same speed through a _______
(300,000,000m/s), and different wavelengths are absorbed by different
surfaces (e.g. infra red is absorbed very well by ___________ surfaces).
This absorption may heat the material up (like infra red and _______) or
cause an alternating current (like in a __ _______).
Words – black, microwaves, long, short, TV aerial, vacuum
The Electromagnetic Spectrum
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Type of radiation
Uses
Dangers
Gamma rays
Treating cancer,
sterilisation
Cell mutation
X rays
Medical
Cell mutation
UVA, UVB and UVC
Sun beds
Skin cancer
Visible light
Seeing things
None (unless you
look at the sun)
Infra red
Remote controls,
heat transfer
Sunburn
Microwaves
Satellites, phones
Burns
TV/radio
Communications
Very few
P1d – Light and Lasers
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Sending Signals
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Ever since the dawn of humanity, humans have been thinking of
effective and fast ways of sending signals:
What are the advantages
and disadvantages of
using sound and light?
Using Light to send Signals
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Morse code is a signal that consists of
short bursts and long bursts and
therefore is classed as a “digital”
signal as each message can be one of
only two forms. These signals could be
relayed between ships over long
distances.
Modern signals can be sent by radio or electric signals
instead. What are the advantages of these methods over
using light?
Finding the Critical Angle…
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1) Ray gets refracted
3) Ray still gets refracted (just!)
THE CRITICAL
ANGLE
2) Ray still gets refracted
4) Ray gets
internally reflected
Uses of Total Internal Reflection
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Optical fibres:
An optical fibre is a long, thin, _______ rod made of
glass or plastic. Light is _______ reflected from one
end to the other, making it possible to send ____
chunks of information
Optical fibres can be used for _________ by sending
electrical signals through the cable. The main advantage
of this is a reduced ______ loss.
Words – communications, internally, large, transparent, signal
Lasers
18/07/2015
Lasers produce light waves that are “coherent” – i.e. they have
the same frequency and they are in phase:
These two waves have
different amplitudes but
the same frequency and hit
their peaks at the same
time – they are “in phase”
Lasers produce an intense, coherent beam of
light where the waves all have the same
frequency (i.e. they’re the same colour), they
are all in phase and they have a low
divergence (they don’t spread out). Because
of these properties lasers can be used for
surgery, cutting materials and weapon
guidance.
Using lasers in CDs
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Information on the
bottom of CDs is stored
digitally, i.e. in the form
of “offs and ons” or
“bumps and pits”. A
typical CD will contain
billions of pits.
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P1e Cooking and Communicating Using Waves
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The Electromagnetic Spectrum revisited
Gamma
rays
γ
X-rays
Ultra violet
Visible
light
Infra red
Microwaves
Radio/TV
Radiation Revisited
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Radiation is when heat moves around in electromagnetic _________ like
light does. Any hot object will emit heat radiation – the hotter it is, the
more radiation it emits. This type of radiation is called __________, and
too much of it will cause _________. Dark, matt colours will absorb AND
emit the _____ infra-red radiation, and light, shiny colours will ________
it.
The main difference with radiation is that conduction and convection could
ONLY happen in solids, liquids or gases, whereas radiation will happen
through an _____ _____. This is just as well, as otherwise we wouldn’t be
able to get any heat from the ___.
Words – sun, reflect, infra-red, waves, most, empty space, sunburn
Anything HOT emits HEAT RADIATION – the hotter it
is, the more infra red radiation it emits
Investigating Radiation
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Here’s an object giving out heat.
Design an experiment that investigates
how the amount of radiation from a hot
object depends on:
• Colour
• Surface area
• Whether it is shiny or matt
Conclusion: What is the best colour and design for the
radiators in your house?
Microwaves vs Conventional Ovens
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In a conventional oven ____ __ radiation is
absorbed by the ____ of the food, causing
the particles there to vibrate with more
_______ energy. That energy is then
transferred to the particles inside the food
by ________ or convection.
In a microwave oven microwaves
penetrate into the food and are absorbed
by ____ molecules, causing them to warm
up. Microwaves pass through glass and
______ and can cause _____. Higher
frequency microwaves penetrate deeper.
Words – burns, water, kinetic, infra red, surface, plastics, conduction
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Using Microwaves for Communication
The trouble with optical fibres and electrical connections is
that they need wires. This is a big advantage with sending
information using microwaves, such as when you use your
mobile phone. However, they have disadvantages as well...
Using Satellites with microwaves
18/07/2015
Microwaves
are used to
communicate
with satellites
Blocking reception
Microwaves can be blocked by
obstructions or, if very large
distances are involved, simply by the
curvature of the Earth
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Weather Conditions
Microwaves can be interfered with
by other mobile signals or by adverse
weather conditions.
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Overcoming these problems
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To try to deal with these problems, mobile phone operators
place their masts in high places and limit the distance between
them:
Dangers of Mobile Phones
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Many people are concerned with the possible
dangers of using mobile phones, especially for
children.
Your task:
Find out about some of the research that has taken place in
the last 20 years over the use of mobile phones, including:
1) Some evidence that using them is dangerous
2) Other evidence that it isn’t
3) Whether or not living near mobile phone masts is dangerous
4) How coming to an overall conclusion can be difficult
Using Infra Red waves
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Some examples:
Remote controls – the signal from the
remote contains a set of digital codes that
carry different instructions to the device.
Short distance data links
Passive infra red detectors that detect
body heat
Analogue vs. Digital
Analogue signals (like talking or
music) continually vary in
amplitude and/or frequency
1
0
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+
Digital signals, however, are either
off or on, and the information is sent
in a series of pulses
There are two main advantages of digital:
1) More channels can be sent down the same cable – “multiplexing”
2) Better quality, because a digital signal can be amplified without
amplifying the extra noise:
P1g – Wireless signals
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Reflecting Radio waves
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Radio waves are refracted and then reflected off the
ionosphere (an electrically charged layer in the atmosphere),
which is useful as they can travel further distances.
Refraction at the Atmosphere
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Different layers of the atmosphere have different refracted
properties, so the path of radio waves can change when it hits
the boundaries between layers:
Using different radio frequencies
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If you have nearby radio transmitters transmitting similar
frequencies then they will interfere with each other. To avoid
this they will transmit signals at different frequencies.
Using Satellites with microwaves
18/07/2015
Microwaves
are used to
communicate
with satellites
Wireless Technology
18/07/2015
These days, many devices work on wireless electromagnetic signals:
What are the advantages
of using wifi over cables?
DAB vs Analogue radio
18/07/2015
Advantages of DAB:
- More stations
- Less interference between
stations
Disadvantages of DAB:
- Poorer audio quality
- Less coverage
P1h – Stable Earth
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Earthquakes
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Earthquakes can be detected by or cause the following:
Waves revision
Transverse waves
are when the
displacement is at
right angles to
the direction of
the wave…
Longitudinal waves
are when the
displacement is
parallel to the
direction of the wave…
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The Structure of the Earth
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A thin crust 10-100km thick
A mantle – has the
properties of a solid
but it can also flow
A core – made of
molten nickel and iron.
Outer part is liquid
and inner part is solid
How do we know this? These facts have all been
discovered by examining seismic waves (earthquakes)
Seismic waves
Earthquakes travel as waves through the Earth – we call them
SEISMIC WAVES. There are two types:
P waves:
1) They are longitudinal so they cause the ground
to move up and down
2) They can pass through solids and liquids
3) They go faster through more dense material
S waves:
1) They are transverse so they cause the ground
to move from right to left
2) They ONLY pass through solids
3) They are slower than P waves
4) They go faster through more dense material
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Seismic waves
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S waves will only travel
through a solid
P waves travel through
the Earth and are
refracted when they
pass through a medium
The paths of these
waves are all curved
because density is
gradually changing
These observations tell us 3 things about the Earth: 1) It has a thin
crust, 2) it has a semi-fluid mantle where density increases with depth,
3) a core with a liquid outer part and a solid inner part.
Suncream
18/07/2015
Ultra violet radiation in sunshine can be dangerous and cause
skin cancer, cataracts and premature skin aging.
It is recommended that you spend no more than 20
minutes in the sun on a sunny day. However, you
could also use suncream:
Safe time = exposure time (e.g. 20 mins) x sun block factor
Having darker skin also helps as more UV is absorbed at the
surface and less reaches the underlying body tissue.
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Warning the Public about UV Dangers
Over the last few years the public has received many warnings
about the dangers of ultraviolet radiation:
Ozone
18/07/2015
Ozone is a chemical (O3) in the atmosphere that absorbs
harmful UV rays from the sun. Unfortunately, it’s getting
thinner:
Diagram showing the quantity
of ozone in different parts of
the southern hemisphere
Global production of CFCs
over the last 60 years –
notice the change!
Verifying Ozone Data
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The discovery of the depletion of
ozone over Antarctica in the 1980s
was unexpected.
Scientists have grown
increasingly confident of the
facts about ozone depletion
due to:
1) Repeating measurements with
new, improved equipment
2) Repetition of measurements
by different scientists
3) Verification of predictions