Electromagnetic Spectrum

Keith Warne

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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