Transcript Waves and Radiation - Welcome to Island School Physics

The EM Spectrum
Lesson 01: Dispersion
Lesson 02/03: The EM Spectrum
Lesson 04: Pupil Research
Lesson 05: Pupil Presentations
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EM Double and Triple Science Syllabus
The electromagnetic spectrum
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understand that light is part of a continuous electromagnetic spectrum which includes radio,
microwave, infra-red, visible, ultraviolet, X-ray and gamma ray radiations and that all these waves
travel at the same speed in free space
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recall the order of the electromagnetic spectrum in decreasing wavelength and increasing
frequency, including the colours of the visible spectrum
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recall some of the uses of electromagnetic radiations, including
 radio waves: broadcasting and communications
 microwaves: cooking and satellite transmissions
 infra-red: heaters and night-vision equipment
 visible light: optical fibres and photography
 ultraviolet: fluorescent lamps
 X-rays: observing the internal structure of objects and materials and medical applications
 gamma rays: sterilising food and medical equipment

recall the detrimental effects of excessive exposure of the human body to electromagnetic waves,
including
 microwaves : internal heating of body tissue
 infra-red : skin burns
 ultraviolet : damage to surface cells and blindness
 gamma rays : cancer, mutation
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Dispersion
17/07/2015
Aim:
• To be able to explain the cause of dispersion
• To explain the nature of the electromagnetic
spectrum
Starter:
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Dispersion
The white light ray is
split into a spectrum of
colours. This is known as
DISPERSION.
The different colours of light
have different wavelengths.
Different wavelengths are
refracted different amounts.
How
do youOf
remember
order
of the In
colours?
Richard
Yorkthe
Gave
Battle
Vain
Which colour is refracted the most?
Red light is refracted least.
Violet light is refracted the most.
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Colour, Wavelength and Amplitude
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Newton’s Disk
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Dispersion Summary
Red/violet
Red/violet
Refracted more/less by
glass
Refracted more/less by
glass
Longer/shorter
wavelength
Longer/shorter
wavelength
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Addition of Colours
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There are three primary
colours:
 Red
 Blue
 Green
By adding together the
primary colours you can
make other colours. For example red and blue
make green.
This is different to the reflection of light this is
an optical illusion due to the way your eyes work.
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Colour Blindness
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No functioning cones:
 See black and white, have problems with daylight, because it is too
bright for them; they also lack visual acuity
One type of cone working:
 see colours only as variations in intensity, similar to black-and-white
or one colour images
Red Cone Not Working:
 typically only two (yellow, blue) can be distinguished - yellow
comprises red, orange, yellow, and green, blue coincides with blue and
purple
Green cone not working;
 green cannot be distinguished from certain combinations of red and
blue; this is the most common type of colour deficiency
Blue cone not working:
 longer wavelengths appear as red and the shorter ones as bluishgreen; this colour deficiency is very rare
More than 8% of the male and about 0.04% of the female population
have some sort of colour anomaly or deficiency.
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Tests
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Which is Longer?
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A Spiral?
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Definitions
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Copy
All Electromagnetic waves are energy waves
They can travel through a vacuum
They all travel at the speed of light (300 000 000
m/s)
We group them by their properties and hence uses,
inside each group is a range of frequencies.
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Electromagnetic Spectrum
Wavelength () increases
Radio
Micro
Most penetrating
InfraRed
High energy
Light
Short wavelength
UltraViolet
X rays
Gamma
High frequency
Low frequency
Highfrequency
frequency
Low
Long wavelength
Shortwavelength
wavelength
Long
Low energy
Highenergy
energy
Low
Least penetrating
Most penetrating
Least
penetrating
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The EM Spectrum
recap
Aim:
• To explain the dangers and uses of the EM Spectrum
Starter:
Light, a type of radiation, is part of the
electromagnetic spectrum.
The electromagnetic spectrum is made
up of different types of radiation.
The different types of radiation have
different properties and behaviour.
All electromagnetic waves can travel
through space.
All electromagnetic waves travel at the
same speed in a vacuum [300,000,000
m/s].
TRUE/FALSE
TRUE/FALSE
TRUE/FALSE
TRUE/FALSE
TRUE/FALSE
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The Electromagnetic Spectrum 17/07/2015
Aim:
• To explain the uses and dangers of the EM Spectrum
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Electromagnetic Spectrum
Wavelength () increases
Radio
Micro
InfraRed
Light
UltraViolet
X rays
Gamma
High frequency
Remember
Low frequency
Short wavelength
My
Long wavelength
High energy
Instructions
Low energy
Most penetrating
Visible
Least penetrating
Under
X – Ray
Glasses
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Uses and dangers of EM radiation
Copy the Top of the following table into your books
(we will fill it in as we go)
Radiation
Uses
Dangers
Gamma
X-rays
Ultraviolet
Light
Infra red
Microwaves
Radio waves
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Microbes can be
killed using gamma
radiation
High
Level
nuclear
waste
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Increasing
dose
healthy
brain
tissue
tumour
view through
the head
Gamma rays can be used
to treat brain tumours
skull
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EM Radiation:
Gamma
Uses:
sterilising surgical
equipment and food,
killing cancer cells.
Dangers:
High doses can kill cells.
Lower does can cause cancer
(brain, liver, bone, leukemia…)
Sterility
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X-ray
tube
Jumbo jet wings are
regularly checked in
this way to see if any
micro-cracks have
developed. These small cracks are too small to
see any other way and could have fatal
consequences.
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X-ray
tube
Detection of broken
bones in the body
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Customs
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X-Rays are used to scan luggage in customs
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Movie
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Damage to organs.
X-rays can penetrate
to the vital organs
inside the body.
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EM Radiation:
X rays
Uses:
Shadow pictures of
luggage and inside the
human body.
Dangers:
High doses can kill cells.
Lower doses can cause
cancer
Sterility
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UV
39637
Visible light
(longer wavelength)
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Movie Friends
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The effect of UV on cells
Outer dead skin cells Outer dead skin cells
Living skin cells
Living skin cells
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EM Radiation:
Ultraviolet
Uses:
Sun beds, fluorescent
lamps and security
marking.
Dangers:
Sun Burn.
Skin cancer
Blindness
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Movie Shorter Wavelengths
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Optical Fibres
Optical
Whatfibres,
are thethat are
used
applications
in communication,
of
use
total
total
internal
internal
reflection.
reflection?
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EM Radiation:
Light
Uses:
Photography and
endoscopes
Dangers:
Blindness
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During the day
the earth warms
up as it absorbs
short wave
infrared rays
from the sun
During the night the earth
loses longer wavelength
infrared rays by
radiating them
into space
and the earth
cools down.
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Too much water
vapour and carbon
dioxide in the
atmosphere will
trap the infrared
rays and cause
the earth to overheat
This effect is
called the
greenhouse
effect
(or global
warming)
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How do infrared waves cook food?
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Night vision
All objects above absolute zero
emit infrared radiation. The hotter
an object is, the more heat
radiation it emits. Some animals
and cameras can detect infrared
radiation and are able to build up
a heat picture.
Which are the
hottest/coolest parts of
the image shown?
light is hot
Walking in the
Woodland
Fireman
dark is cold
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Uses of infrared – activity
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EM Radiation:
Infrared
Uses:
Remote controls, radiant
heaters, grills, optical fibre
communication, night vision,
Mobile Phones
Dangers:
Skin burns
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Communications
satellites use
microwaves
The microwaves can
pass straight through
the ionosphere
Their shorter wavelength
(higher frequency)
means they are more
penetrating than radio
waves
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Microwave oven
The microwaves
You
will need to understand
have the exact
howwavelength
microwaves
cook food to be absorbed by the water
(frequency)
molecules
The molecules move faster
The water temperature
increases
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Demo
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DO NOT do this at Home
Beaker with water in the microwave
Light Bulb in the beaker
Heat for 5 seconds (until the light bulb lights)
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EM Radiation:
Microwaves
Uses:
Satellite communication,
mobile phones, cooking,
RADAR.
Dangers:
Internal tissue
heating.
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Short wave radio and TV waves are
broadcasted to line of sight aerials.
They cannot travel large distances because of
the curvature of the earth.
aerial 1
aerial 2
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Short wave radio and TV waves are
broadcasted to line of sight aerials.
They cannot travel large distances because of
the curvature of the earth.
transmitter
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Radio waves can reach the aerial if we use
a charged layer in the atmosphere (the
IONOSPHERE).
IONOSPHERE
The radio waves are reflected by this charged
layer
Remember that all types of light waves
(electromagnetic radiation) can be reflected
aerial
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EM Radiation:
Radio waves
Uses:
Communication and
astronomy.
Dangers:
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Movie Longer Wavelengths
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The electromagnetic spectrum
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Energy of electromagnetic waves
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Effect of electromagnetic waves
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EM Questions
1)
Match up the following parts of the
electromagnetic spectrum with their uses :
Gamma rays
Allow us to
see
Radio waves
Controls
Ultra Violet
Visible
signals
Microwaves
Remote
‘See’ broken bones
Carry TV
RADAR
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EM Questions
2) Which radiations are missing from below?
Gamma
A
Ultraviolet
Light
Infrared
B
Radio waves
A. ___________
X rays
Microwaves
B. ___________
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Electromagnetic Spectrum
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Movie Uses of EM Spectrum
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The EM Spectrum
recap
Aim:
• To explain the dangers and uses of the EM Spectrum
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Research 17/07/2015
Aim:
• Prepare a presentation on part of the EM
Spectrum
Task:
• Groups of 2 or 3
• Your presentation should last 3-4 minutes
• Everyone must talk
• You must explain at least the uses and dangers
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Pupil Presentations 17/07/2015
Aim:
• Make a presentation on your part of the EM
Spectrum
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