Transcript Waves - Dispersion and Electromagnetic Radiation

KS4 Waves :
Dispersion and
Electromagnetic
radiation
© Boardworks Ltd 2003
After this presentation you will be able to:
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Define dispersion.
Describe how different colours are refracted different amounts.
List the order of radiations in the electromagnetic spectrum.
Recall the uses and dangers of the radiations in the
electromagnetic spectrum.
Describe how radio waves are reflected and diffracted.
Recall the effect of EM radiation on living tissue.
Describe how X ray images are formed.
Describe the effects of incident EM radiation on materials.
Recall the different absorption of EM radiation by different
coloured skin.
Explain how microwaves can heat up foods containing water.
Describe how infrared radiation can be used to form ‘heat
images’.
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Dispersion Experiment
1. Connect a ray box to a
power source.
2. Place a prism on a
piece of plain paper.
The ray box will get
very hot.
Take care!!!!!
3. Draw around the prism.
4. Shine a ray of light at
the prism.
5. Draw in rays of light to
show your observations.
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Explaining 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
the order
of the In
colours?
Richard
York Gave
Battle
Vain
Which colour is refracted the most?
Red light is refracted least.
Violet light is refracted the most.
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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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The Electromagnetic Spectrum
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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Colour, wavelength and amplitude
We can see the relationship between colour,
wavelength and amplitude using this animation.
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Electromagnetic Spectrum
Although all e-m waves travel at the same speed, their
wavelength [] and frequency [ƒ] can be different.
Waves that cook food.
Waves that cause
sun-tans.
The properties, dangers and uses of e-m waves depends
on the wavelength [].
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Electromagnetic Spectrum
Wavelength () increases
Radio
Micro
InfraRed
Light
UltraViolet
X rays
Gamma
Gate
X of a phrase
Usually
Letshelp you
Inremember
Radiation
Can
you
think
that would
Low Most
frequency
this order?
High
frequency
Highfrequency
frequency
Low
Long wavelength
Short wavelength
High energy
Short wavelength
wavelength
Long
Low energy
Most penetrating
Highenergy
energy
Low
Least penetrating
Most penetrating
Least
penetrating
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Electromagnetic Spectrum
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Uses and dangers of EM radiation
Research the uses and dangers of the various radiations:
Radiation
Uses
Dangers
Gamma
X-rays
Ultraviolet
Light
Infra red
Microwaves
Radio waves
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EM Radiation:
Gamma
Uses:
Kills harmful bacteria in
food, sterilising surgical
equipment, killing cancer
cells.
Dangers:
High doses can kill cells.
Lower doses can cause
cells to become cancerous.
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EM Radiation:
X rays
Uses:
Shadow pictures of
luggage and inside the
human body.
Dangers:
How do hospital workers
limit their exposure to
Gamma and X rays?
Hospital workers limit
exposure to Gamma and
X rays by standing behind
lead shields or by leaving
the room when the
radiations are being used.
High doses can kill cells.
Lower doses can cause
cells to become cancerous.
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X rays
How are X rays slides formed?
X rays can
penetrate soft tissue
but not b_____.
X
one
rays are a_______
bsorbed
more by some
materials than
others. P________
hotographic
f____
ilm is used to
detect X rays.
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EM Radiation:
Ultraviolet
Uses:
Sun beds, fluorescent
lamps and security
marking.
Dangers:
Which type of radiation is
the most dangerous?
The higher the frequency
of the radiation, the more
dangerous it is. So
gamma is more
dangerous than X rays or
ultraviolet.
High doses can kill cells.
Lower doses can cause
cells to become cancerous.
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Effects of EM radiation on living cells
Ultraviolet
Infra
red radiation
radiationiscan
used
pass
in toasters,
through grills
skin to
and
deeper
radiant
heaters.
tissues.
What
has
on your
skin?
What effect
effect do
do you
you think
think itthe
colour
of the
skin has on
the amount of radiation that passes through it?
The darker the skin, the more ultraviolet radiation is
absorbed, the less can reach into deeper soft tissues.
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EM Radiation:
Light
Uses:
Seeing and endoscopes
Dangers:
Blindness
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EM Radiation:
Infrared
Uses:
Remote controls (TV/VCR),
radiant heaters, grills, optical
fibre communication, night
vision.
Dangers:
Skin burns
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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
dark is cold
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EM Radiation:
Microwaves
Uses:
Satellite communication,
mobile phone networks,
cooking, RADAR.
Dangers:
Internal tissue heating.
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Microwaves
How do microwaves cook foods?
Microwaves can be used in
c_____
ooking because many foods
ater molecules.
contain w____
Microwaves of the right
avelength are able to make
w________
the water molecules r_______.
esonate
This causes the food to get
h____.
otter
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Radio waves
EM Radiation:
Radio waves
Uses:
Communication and
astronomy.
Dangers:
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Radio waves
How do radio signals from the UK reach around the globe?
The longer
wavelength radio
waves from a
transmitter reflect
off the Earth’s
outer atmosphere
(ionosphere).
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Radio waves
How can houses in the shadows of hills receive a radio signal?
All electromagnetic
radiation travels in
straight lines, does it not?
Radio waves diffract around
the hill to the house.
Remember diffraction?
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Getting hotter
If electromagnetic radiation is incident upon a
material what effects could it have?
An alternating current could be induced in the material,
with the same frequency as the incident radiation.
The temperature of the material could increase.
21º C
30º
50º
70º
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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
Remote Controls
Ultra Violet
‘See’ broken bones
Visible
Carry TV signals
Microwaves
RADAR
X rays
Sterilise equipment
Infra Red
Causes sun-tans
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EM Questions
2) Which radiations are missing from below?
Gamma
A
Ultraviolet
Light
Infrared
B
Radio waves
A. ___________
X rays
B. ___________
Microwaves
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