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Radiation and Radiation and LifeLife

M Barker

Shirebrook Academy

(OCR 21st Century)

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P2.1 Types of EM RadiationP2.1 Types of EM Radiation

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Radiation – the basicsRadiation – the basics

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.

Lots of objects (“sources”) emit radiation. For example, consider the sun. The sun, amongst others, emits light and heat:

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LightLight

White light is a mixture of colours:

RED LIGHT is made of “low energy

photons”

PURPLE LIGHT is made of “high energy

photons”

20/04/23The Electromagnetic The Electromagnetic SpectrumSpectrum

Gamma rays

X-rays Ultra violet Visible light

Infra red Microwaves

Radio/TV

Each type of radiation shown in the electromagnetic spectrum has a different wavelength and a different frequency:

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

High frequency, ____ energy

Low frequency, ________ energy

γ

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PhotonsPhotonsLight (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.

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Intensity of light and heatIntensity of light and heat

The heat here is very intense!

The heat here isn’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.

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An example questionAn example questionWhich of these surfaces would warm up the quickest when receiving infra red photons from the sun?

What factors are affecting the answer?

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IntensityIntensityClearly, 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

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IonisationIonisation

Radiation

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

20/04/23P2.2 Radiation and Living P2.2 Radiation and Living TissueTissue

20/04/23Recap on absorbing Recap on absorbing radiationradiationWho 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?

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Mobile PhonesMobile PhonesAdvantages Disadvantages

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Dangers of Mobile PhonesDangers of Mobile PhonesMany 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

20/04/23How do Microwaves heat How do Microwaves heat food?food?

How does the design of a microwave oven protect the user from harm?

20/04/23Introduction to Introduction to RadioactivityRadioactivity

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.

20/04/23Warning the Public about UV Warning the Public about UV DangersDangers

Over the last few years the public has received many warnings about the dangers of ultraviolet radiation:

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OzoneOzone

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!

Ozone is a chemical (O3) in the atmosphere that absorbs harmful UV rays from the sun. This causes chemical reactions in the atmosphere. Unfortunately, it’s getting thinner:

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SuncreamSuncreamUltra 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!

20/04/23Protection against harmful Protection against harmful radiationradiation

A lead screen protecting from x-rays

Containment structures around a nuclear reactor

Physical barriers can be used to absorb radiation, e.g.

The fact that x-rays are absorbed by hard substances makes them very useful:

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P2.3 Global WarmingP2.3 Global Warming

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Principal FrequencyPrincipal FrequencyAll 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”

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The Greenhouse EffectThe Greenhouse EffectWe 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.

Words – methane, global warming, reflected, absorbing, frequency

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”.

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Global WarmingGlobal Warming

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%

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:

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Global Warming PredictionsGlobal Warming Predictions

Data taken from http://en.wikipedia.org/wiki/File:Global_Warming_Predictions.png

20/04/23The Effects of Global The Effects of Global WarmingWarmingThe 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

20/04/2320/04/23The Carbon The Carbon CycleCycle

CO2 in air 1. CO2 is taken

in by plants and algae for photosynthesis and turned into carbohydrates, fats and proteins

2. Plants and algae release CO2 through respiration

3. The carbon taken in by plants is then eaten by animals and the animals that eat them

4. Animals release CO2 through respiration

5. Burning fossil fuels also releases CO2

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The Carbon Dioxide BalanceThe Carbon Dioxide BalanceCarbon 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”

20/04/23P2.4 EM Waves in P2.4 EM Waves in CommunicationsCommunications

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Reflecting Radio wavesReflecting 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.

20/04/23Using Satellites with Using Satellites with microwavesmicrowaves

Microwaves are used to

communicate with satellites as they

are not absorbed by the atmosphere

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Analogue vs. DigitalAnalogue vs. DigitalAnalogue 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 – “multiplexing”

2) Better quality, because a digital signal can be amplified without amplifying the extra noise:

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Transmitting informationTransmitting informationEM waves can also be used as “carrier waves” in order to send a signal:

Signal Carrier wave

Modulated wave Transmitter Wave is demodulated (“decoded”) back into a signal

Light signals can also be sent down optical fibres where they travel for long distances with little absorption:

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Using Light to send SignalsUsing 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?

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Storing Digital SignalsStoring Digital SignalsOne 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.