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Title: Radiation%20and%20Life


1
Radiation and Life
(OCR 21st Century)
W Richards The Weald School
2
P2.1 Types of EM Radiation
3
Radiation the basics
Lots of objects (sources) emit radiation. For
example, consider the sun. The sun, amongst
others, emits light and heat
Wow its hot here!
Im not so bad thanks
When radiation hits a surface it is usually
either absorbed, reflected or transmitted, or a
combination of these things.
4
Light
White light is a mixture of colours
5
The Electromagnetic Spectrum
Each type of radiation shown in the
electromagnetic spectrum has a different
wavelength and a different frequency
Gamma rays X-rays Ultra violet Visible light Infra red Microwaves Radio/TV
Each of these types travels at the same speed
through a _______ (300,000km/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, low, high, TV aerial,
vacuum
6
Photons
Light (and the other types of EM radiation)
travel in packets called photons
Here comes a photon
And another
And another
Higher frequency radiation (i.e. gamma and x
rays) consist of photons of higher energy.
7
Intensity of light and heat
The heat here is very intense!
The heat here isnt so bad... Why?
When a body absorbs radiation the amount of heat
it gains depends on the intensity (power per
square metre per second) and the time of the
exposure.
8
An example question
Which of these surfaces would warm up the
quickest when receiving infra red photons from
the sun?
What factors are affecting the answer?
9
Intensity
Clearly, the intensity of radiation received by
an object decreases the further out the object
is. This is due to two things
  1. The radiation spreads out in a circle
  2. It is also absorbed by the medium it travels
    through

10
Ionisation
Radiation
11
P2.2 Radiation and Living Tissue
12
Recap on absorbing radiation
Who would warm up the quickest when receiving
infra red photons from the sun?
What would happen of either of these people
absorbed too much heat?
13
Mobile Phones
Advantages
Disadvantages
14
Dangers of Mobile Phones
  • 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
  • Some evidence that using them is dangerous
  • Other evidence that it isnt
  • Whether or not living near mobile phone masts is
    dangerous
  • How coming to an overall conclusion can be
    difficult

15
How do Microwaves heat food?
How does the design of a microwave oven protect
the user from harm?
16
Introduction to Radioactivity
Some substances are classed as radioactive
this means that they are unstable and
continuously give out radiation
Radiation
The nucleus is more stable after emitting some
gamma radiation this is called radioactive
decay. Increased exposure to gamma radiation
can cause cancer or cell death.
17
Warning the Public about UV Dangers
Over the last few years the public has received
many warnings about the dangers of ultraviolet
radiation
18
Ozone
Ozone is a chemical (O3) in the atmosphere that
absorbs harmful UV rays from the sun. This
causes chemical reactions in the atmosphere.
Unfortunately, its getting thinner
19
Suncream
Ultra violet radiation in sunshine can be
dangerous and cause skin cancer, cataracts and
premature skin aging.
Of course, wearing clothes always helps!
20
Protection against harmful radiation
Physical barriers can be used to absorb
radiation, e.g.
A lead screen protecting from x-rays
Containment structures around a nuclear reactor
The fact that x-rays are absorbed by hard
substances makes them very useful
21
P2.3 Global Warming
22
Principal Frequency
All objects emit radiation of some kind. The
principle frequency of that radiation depends
on the objects temperature. For example,
consider a Bunsen burner
Blue is a higher frequency than yellow light
objects that are blue hot are often hotter than
yellow hot
23
The Greenhouse Effect
We get heat from the sun
24
Global Warming
Carbon dioxide, methane and water vapour are all
greenhouse gases but they are only present in
small amounts. However, recently this balance
has been getting upset causing this
  • Facts
  • The 10 warmest years of the last century have all
    occurred within the last 15 years
  • Sea level has risen by between 12 and 24cm in the
    last 100 years
  • Rainfall has risen by 1

25
Global Warming Predictions
26
The Effects of Global Warming
The following things could happen as a result of
global warming
1) Food it will be impossible to grow crops in
particular regions
2) More extreme weather conditions due to
increased convection and larger amounts of water
vapour
3) Flooding of low-lying land caused by ice caps
melting and expansion of water
27
The Carbon Cycle
01/06/2019
2. Plants and algae release CO2 through
respiration
1. CO2 is taken in by plants and algae for
photosynthesis and turned into carbohydrates,
fats and proteins
4. Animals release CO2 through respiration
3. The carbon taken in by plants is then eaten by
animals and the animals that eat them
28
The Carbon Dioxide Balance
Carbon dioxide levels in the atmosphere have
remained balanced due to the carbon cycle.
However, over the last 200 years the level of CO2
in the atmosphere has risen due to activities
like
1) Deforestation, which takes away some of the
trees that remove carbon dioxide
2) Burning fossil fuels, which releases more
carbon into the atmosphere that was previously
locked up
29
P2.4 EM Waves in Communications
30
Reflecting Radio waves
Some radio waves are refracted and then reflected
off the atmosphere and suffer little absorption,
which is useful as they can travel further
distances.
31
Using Satellites with microwaves
Microwaves are used to communicate with
satellites as they are not absorbed by the
atmosphere
32
Analogue vs. Digital
Analogue signals (like talking or music)
continually vary in amplitude and/or frequency
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
  • More channels can be sent down the same cable
    multiplexing
  • Better quality, because a digital signal can be
    amplified without amplifying the extra noise

33
Transmitting information
EM waves can also be used as carrier waves in
order to send a signal
Light signals can also be sent down optical
fibres where they travel for long distances with
little absorption
34
Using Light to send Signals
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?
35
Storing Digital Signals
One of the advantages of digital signals is that
they can be stored and processed easily by
computers.
Data is measured in units called bytes. 1 Byte
8 bits, and is roughly the amount of data
needed to store one character of text.
Clearly, the large a file size, the more bytes it
contains and therefore the higher quality the
sound or image is.
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