National 4
Unit 1: Section 4
• I can describe applications and hazards associated with
electromagnetic radiations.
• I can describe approaches to minimising risks associated with
electromagnetic radiations.
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National 5
Unit 1: Section 4
• I can state the relative frequency and wavelength of radiations
in the electromagnetic spectrum
• I can state some typical sources and applications of radiations in
the electromagnetic spectrum.
• I can state the relationship between the frequency and energy
associated with a form of radiation.
• I can state that all radiations in the electromagnetic spectrum
travel at the speed of light
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Unit 1: Section 4
By the end of Unit 1 Section 4
I will have:
• Researched the safety of Microwaves in mobile communication
and presented my findings for consideration by my peers in a
suitable format.
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The Electromagnetic Spectrum
Energy often travels through space in the form of electromagnetic
waves. This family of waves include:
They all travel through space at a speed of 3 x 108 m s−1
(300 000 000 m s−1). Each member of the electromagnetic spectrum
has a different ___________ and _____________.
Radio and Television
Mobile telephones (microwaves), radio and
television are examples of long-range
communication which do not need
_________ between the transmitter and
the receiver. These signals travel as waves
and so carry _________. They also travel
very quickly - their speed in air is
300 000 000 ms−1 (___________ms−1).
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Experiment 1
What you need: Battery, file, radio.
battery
file
What to do:
Switch on the radio and place it near the file. Scrape the end of the
wire quickly over the file. Move the radio further away and again
scrape the wire over the file.
Questions:
1. What effect does scraping the file have on the radio?
__________________________________________________
2. How far apart can you move the radio and the file and still hear
the effect?
__________________________________________________
3. There are no wires joining the file to the radio - how does the
signal travel to the radio?
__________________________________________________
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Experiment 2
What you need: Radio, I-pod, aluminium foil, plastic bag.
What to do:
• Switch on the radio and tune to a station - then wrap it in
aluminium foil.
• Switch on the I-pod and wrap it in aluminium foil.
• Repeat using the plastic bag instead of the aluminium foil.
Questions:
1. Can radio waves pass through metal foil?
2. Can radio waves pass through plastic?
3. Would this radio work well inside a metal train or car?
4. How is a car radio able to pick up radio waves?
5. What happens when the I-pod is wrapped in foil?
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Tuning
Radio sets and Television sets are able to receive signals
from many different stations. To keep the signals
separate, each station transmits on a different
______________ (and therefore different frequency).Inside radio
sets and television sets there are tuning circuits which when altered
accepts only _____ signal and ignores all the rest.
Experiment 3
What you need: Radio set
Tune into some of the stations listed below. Complete the
table.
Working
Station
Radio Scotland
Radio 1
Radio Clyde
Clyde 2
Radio 4
Atlantic
Wavelength
370 m
275 m
261 m
Frequency
810 kHz
1089 kHz
102.5 MHz
1515 m
1190 m
252 kHz
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Wave Band
MW
MW
MW
Fm
LW
LW
Microwaves
Microwaves are used in satellite communication or short
range terrestrial (on Earth) communication.
Microwaves have smaller wavelengths than Radio and T.V. waves and
so can’t _____________ around objects.
Microwaves are also used for
__________________________________________
__________________________________________
__________________________________________
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Do you consider mobile phones to be safe?
The use of mobile phones is a good example of a scientific
controversy. Recent research studies have produced tentative
evidence that mobile phones may have long-term health effects.
However, this is by no means certain and the radiation produced by
mobile phones falls well below current safety guidelines.
Activity
1. Find the website – www.peep.ac.uk
2. Read each webpage on this topic in turn carefully
3. Look at the extra links and interviews
4. Considering evidence for and against the use of mobile phones,
use this framework to construct a reasoned argument and
present it in a suitable format. Use the cues below to help you.
I think that................................................
The evidence to support this idea is.....
The evidence supports me because........
Arguments against me are........................
I would counter these arguments by........
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Questions
1. Our eyes can detect visible light with wavelengths
ranging from 400 nm to 700 nm. Light with a wavelength of
around 400 nm is violet in colour. Red light has a wavelength of
around 700 nm.
[ 1nm = 1x10-9m]
Calculate the frequencies of violet light and red light.
2. The human body gives out microwaves of wavelength 9 cm which
can be detected by a small aerial placed in contact with the skin.
These microwaves allow doctors to measure the temperature of
organs inside the body.
Calculate the frequency of microwaves emitted from the body.
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Satellite Communication
Experiment 4
What you need: Raybox kit, curved reflector, labpack, ruler
Place a set of slits in the beam to produce three parallel rays of light
- draw in what happens to the rays.
1. What happens to the beam of light after it hits
the mirror?
2. Where is the light brightest?
3. Why are curved reflectors (dishes) used in communications?
4. Where should the receiving aerial be placed so that it receives the
strongest signal from the dish?
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Visible Light - Lasers
A laser produces an intense _________ of
_________ in ______ direction.
Lasers have various uses in medicine. For example:
Vaporising Cancer
Tumours
Laser Scalpel
Eye Surgery
Removing
Tattoos/Birth Marks
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Infrared
All ______ objects give off invisible ‘heat rays’ called
infrared radiation. Infrared radiation travels at
___________________________.
Special infrared cameras can be used to take colour photographs
called _______________ using this radiation instead of light.
In medicine, thermograms of a patient’s body show areas of
different temperature as different ____________. Doctors have
found that malignant tumours are ____________ than healthy
tissue and show up clearly on thermograms.
Infrared radiation is used in a different way by physiotherapists.
They use this radiation to penetrate the skin and heat muscles and
tissues. Heat causes healing to occur more quickly.
Infrared light is also used in Nightvision devices, and in astronomy,
imaging at infrared wavelengths allows
observation of objects obscured by
interstellar dust.
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Experiment 5.
What you need: Light source, prism, infrared detector,
gauze, Bunsen and tongs
What to do:
1. Using the tongs, heat the gauze in the Bunsen flame until it glows
red hot.
2. Take it out and let it cool until the red glow just disappears.
3. Hold the gauze in front of the radiation sensor. Note how the
detector reading changes when the gauze is brought close to it.
4. Move the detector beyond the red. Note the reading on the meter.
Explain why the meter reading changes beyond the red end of the
spectrum.
Experiment 6
What you need: Infrared thermometers
What to do: Use an Infrared thermometer to measure various
temperatures around the lab.
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Ultraviolet
Ultraviolet is another type of invisible radiation which
travels at _______________________.To keep healthy, our bodies
need the ultraviolet radiation to produce _______________ to help
the body obtain calcium from food.
Too much ultraviolet light on the skin produces _____________.
Excessive use of sun beds may cause _________ _________.
Ultraviolet radiation is used in the treatment of Jaundice in babies
and certain skin diseases such as acne.
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Fluorescence
Some chemicals glow and emit visible light when they absorb UV. This
is used in shops to test credit card and banknotes as they have codes
marked on them that cannot be seen in normal light but glow under a
UV lamp
Industry uses fluorescent plastic food seals on some products to allow
automatic checks for tampering.
Experiment 7
What you need: Ultraviolet lamp, "Invisible ink"
security marker, various banknotes, credit cards, white shirt, soap
powder, highlighter ink, UV beads.
What to do:
Use the ultraviolet lamp to examine each of the samples.
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X-rays
X-rays are invisible rays which _________ photographic
film when they hit it and travel at ________________________.
X-rays pass through body tissues like skin, fat and muscle fairly
easily, but are more readily absorbed by __________.
Medical X-rays
X-rays are used in two main areas in
medicine – diagnosis and treatment.
•
X-rays are used to diagnose
illness, or damage to bones or
other tissues inside the body.
•
High energy X-rays are used to
intentionally damage cancerous cells.
When X-rays hit the photographic plate
on the other side of the patient, they
blacken the photographic film, and so
the image of the foot would be fairly
dark, with lighter areas for the bone.
Any break in the bone lets
X-rays
through and may show up as a dark
crack.
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People who work with X-rays must be protected from the X-rays.
They use lead screens to block the X-rays, they stand as far as
possible from the machine and they wear special photographic film
badges which monitor their exposure
X-rays may also be used to look for problems in organs or the
intestine. Patients swallow a liquid which absorbs X-rays - a ‘barium
meal’. The X-rays are detected electronically, processed by a
computer and produce an image on the monitor.
X-rays Photographs
Experiment 7
What you need: X-ray transparencies.
What to do: Hold the X-ray transparency up to light – identify which
part of the body has been X-rayed.
1. Why is X-ray film put in light tight containers?
2. If X-rays of wavelength 3 x 10−11 m are used for on a patient
calculate their frequency?
3. What advantages can you think of in using continuous X-ray
pictures?
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Computed Tomography
Computed tomography uses a sophisticated X-ray machine
known as a CAT scanner to give a clear image of a selected slice
through the body. The X-rays travel at right angles to the body’s
length as shown below, and the source and detector rotate around
the body to give readings for all directions.
The data is fed into a computer which then builds up a picture of the
organs in each slice. The picture is then displayed on a TV screen.
The main advantages of computed tomography compared with normal
X-ray photographs are
• a three dimensional picture of the part of the body being
studied (hence nothing is hidden)
• moving pictures can be obtained.
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Gamma Radiation (γ)
Gamma radiation, also known as gamma rays is an invisible
electromagnetic radiation with _______ energy, which
can pass through thick layers of most materials.
Treating Cancer - Radiation Therapy
Cancers are growths of cells which are out of control. The radiation
____________ the cancer cells which then stop reproducing. The
cancer or tumour then _____________.
__________ cells can also be damaged by radiation, and so the
applied dose has to be very accurately calculated.
The apparatus is arranged so
that it can rotate around the
couch on which the patient lies.
This allows the patient to be
irradiated from different
directions.
The tumour receives a maximum
radiation dose from the beam, while
the skin and other tissue receive as
little unwanted radiation as possible.
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Questions
1. A patient is suffering from pains in his knees. The doctor in the
hospital takes a thermogram of the knees and detects an
inflammation of the joints caused by arthritis. The infra red
radiation being given out by the knees has a frequency of
5 x 1012 Hz.
Calculate the wavelength of this radiation.
2. The ancient Egyptians used ultraviolet radiation from the sun’s
rays to treat the skin complaint acne. Ultraviolet light is still
used today in hospital to treat acne.
Calculate the wavelength of UV light of frequency 8·8 x1016 Hz.
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3. X – rays are widely used in medicine and dentistry.
4.
John is having an X-ray taken of one of his teeth. The dentist
sets up the X-ray apparatus and goes to stand behind a lead
screen. The X - rays used have a frequency of 2 x1017 Hz.
(a)
Calculate the wavelength of these X-rays.
(b)
How long will it take for these X -rays to travel 10 cm
from the X- ray machine to John’s tooth?
(c)
Why did the dentist stand behind a lead screen?
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Unit 1: Section 4 - Additional notes
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Unit 1: Section 4 - Additional notes
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Unit 1: Section 4 - Additional notes
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Unit 1: Section 4 - Additional notes
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