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Light

As we have already seen light is an electromagnetic wave
All electromagnetic waves are similar
They are transverse

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Frequency is the number of seconds per wave and is
measured in Hertz ( Hz )




Wave Equation for Light




v = Speed ( velocity ) of the wave in cm / s or m / s
f = Frequency in Hertz ( Hz )
= wavelength in cm or…

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Using light for communication

Centuries ago smoke signals and bonfires were used to
communicate
Communication became easier after electric light was
invented
Samuel Morse invented the Morse code which is a system
of dots and dashes representing letters and numbers

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The Morse code

Mirrors and signalling lamps have been used to send
messages using the Morse code
The code is a series of dots and dashes that represent
individual letters of the alphabet

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Advantages and Disadvantages of communications

Method Advantages Disadvantages
Light Sends messages very Light easier to see in
( e.g. Morse fast, almost instantly dark
code and Send from anywhere Not private
lighthouses ) Have to be in line of
sight
Radio waves Low energy waves You can get interference
Not…

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Lasers

L ight
A mplification by
S timulated
E mission of
R adiation

A laser is a very narrow, high energy, intense beam of
light
It is very intense because all the waves have the same
frequency and are in phase




Laser light

White light, from a bulb, is made…

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The light from a laser is at one frequency and in phase

Laser light

The crest and troughs appear at the same time




White light

The crests and troughs do not appear at the same time




Compact disks

Lasers are used to read compact disks, by reflecting of a
series…

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The music layer is coated with a fine film of metal that
follows the pits exactly
The shiny metal film reflects the lasers light
The metal layer is covered by another layer of fine plastic
The music is sandwiched between two layers of plastic
This stops dust and scratches from…

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