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A set of slides created to teach Electromagnetic Spectrum to learners at Bishops Diocesan College in Cape Town.
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Electromagnetic Spectrum
Keith Warne
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For FULL presentation click HERE >> www.warnescience.net
Electromagnetic Waves
Transmitter
(Signal generated alternating current)
Receiver:
(Signal Received –weak alternating current induced –needs amplification)
Right Hand Dynamo Rule
EM waves can be generated and detected by changing(accelerating) electric currents in a conductor (arial)
Direction of movement
Field
Current
Thrust/movement
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Electromagnetic Spectrum
All the different types of electromagnetic waves form the Electromagnetic Spectrum.
Changing the frequency changes the properties of the waves.
INCREASING FREQUENCY and ENERGY
INCREASING W A V E L E N G T H
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Microwaves
Microwaves have wavelengths that can be measured in centimeters!
The longer microwaves, those closer to a foot (~30 cm) in length, are the waves which heat our food in a microwave oven.
Microwaves are good for transmitting because microwave energy can penetrate haze, light rain and snow, clouds, and smoke.
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Visible Light
Visible light is made up of the various frequencies of colored light.
The colour is determined by the frequency of the light. When electromagnetic radiation of this frequency falls
on our retina our brain interprets it as colour.
Longer wavelengths are refracted the LEAST!
Energy of a Light
• Energy of a photon E = hf Max Planck
• Wave equation = f x
• speed of light = c
To calculate the energy of a photon of light with
wavelength and speed c
.: E = h(c/ )
h = 6.63 X 10-34 J.s
Eg, Calculate the energy of a photon of blue light.
E = hf
= (6.63x10-34)*(3x108/450x10-9) = 4.4x10-9J
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Polarization
The electric and magnetic
fields in light oscillate in
ALL DIRECTIONS.
A Polaroid filter allows the
ELECTRIC field through
in ONE PLANE only –
i.e. the light has been
PLANE POLARISED.
If a second Polaroid filter is
placed at 90o to the first
NO LIGHT WILL PASS
THROUGH!
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EM SummaryRadiation Produced Rel. Size Penetration USE
() Radioactive
decay
() Cathode ray
tubes
X High energy
electron
collisions
UV Sun / lamps
Visible White Hot
objects
IR heat
Micro Magneto
Radio Alternating
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Hi…
This is a SAMPLE presentation only.
My FULL presentations, which contain a lot more slides and other resources, are freely available
on my resource sharing website:
www.warnescience.net(paste into your browser if link above does not work)
Have a look and enjoy!
Keith Warne
WarneScience
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