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Waves: Total Internal Reflection and Communication

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1 Waves: Total Internal Reflection and Communication
Give the meaning of critical angle Describe internal and total internal reflection Recall and use the definition of refractive index n in terms of speed Recall and use the equation sin i /sin r = n Describe the action of optical fibres particularly in medicine and communications technology

2 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.

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

4 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.

5 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.

6 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.

7 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

8 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.

9 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

10 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

11 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

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

13 What does attenuation mean?
Strengthening Increasing Larger Weakening


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