1. KS4 Waves: Total Internal Reflection and Communication

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3. Total Internal Reflection
Angle r
Refracted ray
Angle r
Angle i
Incident ray
Reflected ray
At what angle of incidence did the ray change from refraction to reflection?
It depends upon the material you used.

4. Simulation of a ray of light passing through a semi-circular glass block

5. Total Internal Reflection
This angle is called the critical angle [ c]
 i <  c
Refraction
 i =  c
Critical case
 i >  c
Total Internal Reflection
[TIR]
Different materials have different critical angles. Diamond has the lowest at 24º which is why it reflects so much light.

6. The Critical Angle Material Refractive index Critical angle Glass
How does refractive index affect the critical angle?
Research the missing values below and then make a conclusion…
Material
Refractive index
Critical angle
Glass
Water
Diamond
1.5
42°
1.33
49°
2.4
24°
The greater the refractive index the smaller the critical angle.

7. Total Internal Reflection
Optical fibres, that are used in communication, use total internal reflection.
What are the applications of total internal reflection?
You could be asked to draw on the path of the beam in an exam.
A beam of light enters the optical fibre….
…NOTE how it is refracted as it enters the fibre…
…it travels down the fibre through repeated total internal reflections.

8. Optical versus electrical
Research why communications systems now use optical fibres instead of copper wires, use the table below to help you.
Optical
Electrical
Information
Attenuation
Interference
Cost
Carry more
Carry less
Less
More No
Yes
More
Less
How is attenuation solved in optical and electrical fibres?
Regenerators for electrical cables
Repeaters for optical fibres

9. Digital and analogue
What is the difference between a digital signal and an analogue signal?
What could they look like graphically?
Digital signals can only be in one of two states, e.g. 0 or 1.
Analogue signals are a continuously changing variable.

10. Digital compared to Analogue
ADVANTAGES
 Signals are clearer less susceptible to noise.
 Can be used quickly by computers.
 Carry digital signals using electromagnetic waves which travel at the speed of light.
 Carry much more information.
Digital hardware is much smaller.
Easier to send over long distances.
DISADVANTAGES
 Digital hardware is expensive at the moment.
 Although digital signals are unaffected by electrical interference, they don’t give a complete signal [just lots of samples] - some people feel that analogue vinyl records sound better than digital CDs for this reason.
Electrical storms and random thermal noise.
Noise is any unwanted information.
Which signal is most prone to noise?
Which signal carries the most information?
Analogue
Examples of noise are?
What is noise?
Digital

11. Communication systems
Communication systems include the same basic components. You need to be able to define/describe the following:
Modulator
Transducer
Encoder
Transmitter
Amplifier
Storage
Decoder
Receiver

12. Definitions Component Function Encoder Decoder
Modulator
Transmitter
Receiver
Storage
Transducer
Amplifier
Changes information into readable form
Changes information to original form
Allows wave to carry impulses AM/FM
Makes oscillations
Collects information
Stores information e.g. CD, DVD, tape
Changes information into electrical form or the other way round (microphone, speaker)
Increases intensity of received waves

13. AM and FM AM FM What do AM and FM stand for? How do they compare?
AM – amplitude modulation, where the sound wave is communicated by altering (modulating) the AMPLITUDE of the radio wave
FM – frequency modulation, where the sound wave is communicated by altering (modulating) the FREQUENCY of the radio wave
How do they compare?
More noise AM FM
Easier to send
Less noise
More noise
Less noise
Travels further
Travels shorter distances
Harder to send
Travels further
Travels shorter distances
Easier to send
Harder to send

14. Storage and retrieval of information
What methods of storing information do you know?
1. _________________
2. _________________
3. _________________
4. _________________
Magnetic Tape
Analogue
Digital Video Disc - DVD
Digital
Vinyl Records
Analogue
Compact Disc - CD
Digital
Which are digital and which are analogue?

15. Which of the following is not a use of total internal reflection?
Periscopes
Endoscopes
Fibre optic communication
Mirrors 

16. What does attenuation mean?
Strengthening
Increasing
Larger
Weakening 

17. Which of the following is not a a digital storage method?
DVD CD
CD-ROM
Vinyl record 