Radiation and Life This PowerPoint supports the P2 topic from the 2011 OCR 21st Century course W Richards
P2.1 Types of EM Radiation 02/25/13
Radiation – the basics
Lots of objects (“sources”) emit radiation. For example, consider the sun. The sun, amongst others, emits light and heat: Wow it’s hot here!
I’m not so bad thanks
When radiation hits a surface it is usually either absorbed, reflected or transmitted, or a combination of these things.
White light is a mixture of colours: RED LIGHT is made of “low energy photons”
PURPLE LIGHT is made of “high energy photons”
The Electromagnetic Spectrum 02/25/13
Each type of radiation shown in the electromagnetic spectrum has a different wavelength and a different frequency: High frequency, ____ energy Gamma rays
Low frequency, ________ energy Ultra violet Visible light
Îł 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 â€“ black, microwaves, low, high, TV aerial, vacuum
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.
Intensity of light and heat
The heat here is very intense!
The heat here isnâ€™t 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.
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?
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 â€œspreads outâ€? in a circle 2) It is also absorbed by the medium it travels through
Some types of radiation are dangerous because they “ionise” atoms – in other words, they change atoms by turning them into _____ by “knocking off” __________:
Ionisation causes chemical reactions which cause _____ in living tissue to mutate, usually causing _______. High doses can destroy cells completely, causing radiation sickness. This takes a lot of ______ so only high energy radiations like ________, x rays and ultra violet can do it.
Words – energy, gamma, electrons, ions, cancer, cells
P2.2 Radiation and Living Tissue 02/25/13
Recap on absorbing radiation 02/25/13
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?
Mobile Phones Advantages
Dangers of Mobile Phones
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 isnâ€™t 3) Whether or not living near mobile phone masts is dangerous 4) How coming to an overall conclusion can be difficult
How do Microwaves heat food? 02/25/13
How does the design of a microwave oven protect the user from harm?
Introduction to Radioactivity 02/25/13
Some substances are classed as “radioactive” – this means that they are unstable and continuously give out 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.
Warning the Public about UV Dangers 02/25/13
Over the last few years the public has received many warnings about the dangers of ultraviolet radiation:
Ozone is a chemical (O3) in the atmosphere that absorbs harmful UV rays from the sun. This causes chemical reactions in the atmosphere. Unfortunately, itâ€™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 â€“ notice the change!
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: Of course, wearing clothes always helps!
Protection against harmful radiation 02/25/13
Physical barriers can be used to absorb radiation, e.g.
A lead screen protecting from x-rays
The fact that x-rays are absorbed by hard substances makes them very useful:
Containment structures around a nuclear reactor
P2.3 Global Warming
All objects emit radiation of some kind. The “principle frequency” of that radiation depends on the object’s 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”
The Greenhouse Effect
We get heat from the sun:
A lot of this heat is _______ back into space. However, most of it is kept inside the Earth by a layer of gases (e.g. carbon dioxide and ______) that prevent the heat escaping by _______ and then re-radiating it back again.
The Earth reflects back radiation with a lower principal _______ that the radiation it receives from the sun. This radiation basically causes the earth to warm up – this is called “_______ ________” or the “Greenhouse Effect”. Words – methane, global warming, reflected, absorbing, frequency
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 â€œupsetâ€? causing this: Facts: 1) The 10 warmest years of the last century have all occurred within the last 15 years 2) Sea level has risen by between 12 and 24cm in the last 100 years 3) Rainfall has risen by 1%
Global Warming Predictions
Data taken from http://en.wikipedia.org/wiki/File:Global_Warming_Predictions.png
The Effects of Global Warming 02/25/13
The following things could happen as a result of global warming:
1) Food â€“ 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
The Carbon Cycle CO2 in air 5. Burning fossil fuels also releases CO2
4. Animals release CO2 through respiration
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
3. The carbon taken in by plants is then eaten by animals and the animals that eat them
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 â€œlocked upâ€?
P2.4 EM Waves in Communications 02/25/13
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.
Using Satellites with microwaves 02/25/13
Microwaves are used to communicate with satellites as they are not absorbed by the atmosphere
Analogue vs. Digital Analogue signals (like talking or music) continually vary in amplitude and/or frequency 1 0
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 â€“ â€œmultiplexingâ€? 2) Better quality, because a digital signal can be amplified without amplifying the extra noise:
EM waves can also be used as “carrier waves” in order to send a signal:
Modulated wave Transmitter
Light signals can also be sent down optical fibres where they travel for long distances with little absorption:
Wave is demodulated (“decoded”) back into a signal
Using Light to send Signals
Morse code is a signal that consists of short bursts and long bursts and therefore is classed as a â€œdigitalâ€? 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?
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 â€œbytesâ€?. 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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