Transcript www.PhysicsGCSE.co.uk P1d(i) Light and Lasers You will learn about: Which factors affect the choice made to send a signal How laser light can be used.

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P1d(i) Light and Lasers
You will learn about:
Which factors affect the choice made to
send a signal
How laser light can be used
www.PhysicsGCSE.co.uk
Early Messages
Smoke signals were sent by
the Ancient Greeks as did
the American Indians. But
their signals did not travel
that far and they were
weather dependent.
Beacons can also be used
to send signals but are
also limited by weather
conditions.
Pigeons can also be used to
send signals. These are faster
so long as the pigeon makes
the journey.
Motorbikes are used
today as they are faster
and more convenient.
Light travels much faster
than any other message
method. Ships today use
light beacons to transmit
Morse Code. Morse code
was in operation by the
Navy until 1999.
LASER is an acronym for:
Light Amplification by
Stimulated Emission of
Radiation.
A laser produces a very
intense narrow beam of
light of a single colour – it
is monochromatic. It can
cut, burn or vaporise
materials.
Lasers can also be used
for:
transmitting
communication signals,
dental treatment,
guiding missiles,
light shown at public
displays, and
bar code readers.
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Morse Code
.. / -.-. .- -. / ... ..- -.-. -.-. . . -.. / .- - /
.--. .... -.-- ... .. -.-. ...
This means:
I can succeed at Physics!
Morse code has been
transmitted using mirrors
and signalling lamps as
well as by sound.
The code is represented
by a series of dots and
dashes.
This is a digital signal
because the dots and
dashes are a series of on
and off signals.
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Sending Signals
Signals can be sent very quickly by light, radio or
microwaves.
ADVANTAGES:
1.
They are almost instantaneous because
all Electromagnetic waves travel at the
same speed.
2.
They can travel huge distances including
through space.
DISADVANTAGES:
1.
Signals need to be coded otherwise
anyone can intercept the message.
2.
Most of these signals need to include
wires or sophisticated electrical
equipment which can easily be cut or
sabotaged. The intended signal may not
be sent.
3.
The signal also needs to be amplified
because the wave energy is easily lost
over large distances.
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The light form these waves is in
phase because the peaks and
troughs occur at the same time.
Laser Light
White light consists of different colours. Each
colour is a different frequency and out of phase.
Light from a laser is at one frequency so it is in
phase.
Laser light is monochromatic which means it is a
single colour from one frequency
and coherent which means the beam is in phase.
CDs
The light form these waves is
out of phase because the peaks
and troughs occur at different
times.
Compact Discs, CDs, are pressed with a series of very tiny
pits. There are billions of these pits and they each represent
a digital signal. The signal is read using a laser.
The music layer has a fine film of metal that coats it which
follows the pits.
This shiny film reflects the laser light.
The metal layer is covered by a tough plastic layer to reduce
any scratching.
This means that the music code is sandwiched between the
two layers.
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Questions
1. Why should you not look directly into a laser
beam?
2. If you watch Star Wars the characters have
laser lightsabers. How easy is it to see a
laser?
3. Why are signals to Italy sent by microwaves?
Why are telephones signals sent to your
house form the local exchange by electric
current?
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Questions
1.
2.
3.
Why should you not look directly into a laser beam?
It may blind you or cut you. It is incredibly dangerous as it is a
very intense narrow beam of light.
REMEMBER: Never shine a laser into anyone’s eyes.
If you watch Star Wars the characters have laser lightsabers. How
easy is it to see a laser?
Very difficult because the beam is no narrow.
Why are signals to Italy sent by microwaves? Why are telephones
signals sent to your house from the local exchange by electric
current?
The further a signal has to travel the more it needs to be
amplified because energy from it is lost as waste, usually heat.
So for long distances microwaves are best as they are fast and
travel long distances.
For local telephone signals wires are fine because the
distances are much shorter. There is also less chance of the
wires being cut or damaged.