P1d: Lights and Lasers

The use of light as a source of digital communication, from Morse signalling to present day laser technology, has made rapid communication possible. This item develops ideas about communication at the speed of light, including applications of Total Internal Reflection.

 

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What four things do the properties of light produced by lasers allow them to be used for?
Surgery and dental treatment, cutting materials in industry, weapon guidance and laser light shows.
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What did the use of light greatly increase?
The use of communication - but involved the use of a code.
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Where does total internal reflection happen?(TIR)
Glass air boundary, Water air boundary and Perspex air boundary
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How can light and infra-red radiation travel along an optical fibre?
By reflection from the sides of the fibre.
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How was light used in means for communication?
Signals sent in the form on morse code which is a series of on and off signals, signals relayed between stations to cover larger distances.
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Why is morse code a digital signal?
It can be transmitted in many different ways, including visible light, radio waves and electrical pulses.
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Advantages (2) and Disadvantage of using light signals for communication.
Doesn't require wires and more secure against eavesdroppers , but needs the transmitter and receiver to be in the line of sight
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Advantages (2) and Disadvantage of using radio signals for communication.
Doesn't require wires and doesn't need the transmitter and receiver to be in the line of sight but isn't very more secure against eavesdroppers.
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Advanatges (2) and Disadvantage of using electrical signals for communication.
Requires wires but doesn't need the transmitter and receiver to be in the line of sight and more secure against eavesdroppers.
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What beam of light does a laser produce?
A narrow beam of light of a single colour (monochromatic)
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Why do most lasers produce an intense coherent beam of light?
Waves have the same frequency, waves are in phase with each other and waves have low divergence.
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How is a laser used in a CD player?
The shiny surface of a CD contains billions of microscopic pits in a spiral track. The pattern of pits contains digital information. The laser light is reflected off the surface of the CD as the disk spins.
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How is the CD detected?
by the change in the amount of reflected light caused by entering or leaving a pit is interpreted as a 1 and no change in the amount of reflected light is interpreted as a 0.
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Light rays and infrared rays change speed when they pass from...
glass to air or perspex to air.
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Why do light rays and infrared rays change speed when they pass from certain materials?
Because of the difference in densities.
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When do the light rays and infrared ray change direction?
When/if they hit the boundary of the material at an angle other than 90°
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What is total internal reflection?
When Beyond a certain angle, called the critical angle, all the rays reflect back into the glass or Perspex.
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What happens to light rays that hit the surface beyond the critical angle?
They become effectively trapped.
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What is the critical angle for glass?
42°
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What is an optic fibre?
A thin rod of high quality glass.
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How much light is absorbed by an optic fibre?
Very little
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What does light going in an optic fibre undergo?
repeated total internal reflection, even when the fibre is bent, and emerges at the other end.
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Name two information signals.
Computer data and telephone calls.
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What can information signals be converted into?
Electrical signals.
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What can electrical signals be carried through or transmitted as?
Carried through cables, invisible light signals, or infrared signals. or transmitted as microwaves, radio waves and as optical fibres.
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What are optical fibres used in medically?
Endoscopes - which allow surgeons to see inside their patients.
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Other cards in this set

Card 2

Front

What did the use of light greatly increase?

Back

The use of communication - but involved the use of a code.

Card 3

Front

Where does total internal reflection happen?(TIR)

Back

Preview of the front of card 3

Card 4

Front

How can light and infra-red radiation travel along an optical fibre?

Back

Preview of the front of card 4

Card 5

Front

How was light used in means for communication?

Back

Preview of the front of card 5
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