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© Boardworks Ltd 2003 Waves: Total Internal Reflection and Communication Give the meaning of critical angle Describe internal and total internal reflection.

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Presentation on theme: "© Boardworks Ltd 2003 Waves: Total Internal Reflection and Communication Give the meaning of critical angle Describe internal and total internal reflection."— Presentation transcript:

1 © Boardworks Ltd 2003 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 © Boardworks Ltd 2003 Reflected ray Total Internal Reflection Incident ray Refracted ray Angle i Angle r At what angle of incidence did the ray change from refraction to reflection? It depends upon the material you used.

3 © Boardworks Ltd 2003 Simulation of a ray of light passing through a semi-circular glass block

4 © Boardworks Ltd 2003 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 © Boardworks Ltd 2003 The Critical Angle How does refractive index affect the critical angle? The greater the refractive index the smaller the critical angle. MaterialRefractive index Critical angle Glass Water Diamond 42° 49° 24° Research the missing values below and then make a conclusion…

6 © Boardworks Ltd 2003 Total Internal Reflection Optical fibres, that are used in communication, use total internal reflection. 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. What are the applications of total internal reflection? You could be asked to draw on the path of the beam in an exam.

7 © Boardworks Ltd 2003 Optical versus electrical Research why communications systems now use optical fibres instead of copper wires, use the table below to help you. OpticalElectrical Information Attenuation Interference Cost Carry moreCarry less LessMore NoYes MoreLess How is attenuation solved in optical and electrical fibres? Regenerators for electrical cables Repeaters for optical fibres

8 © Boardworks Ltd 2003 Digital and analogue What is the difference between a digital signal and an analogue signal? Digital signals can only be in one of two states, e.g. 0 or 1. Analogue signals are a continuously changing variable. What could they look like graphically?

9 © Boardworks Ltd 2003 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. What is noise? Noise is any unwanted information. Examples of noise are? Electrical storms and random thermal noise. Which signal is most prone to noise? Analogue Which signal carries the most information? Digital Digital compared to Analogue

10 © Boardworks Ltd 2003 Communication systems Communication systems include the same basic components. You need to be able to define/describe the following: Encoder Amplifier Decoder Modulator Transmitter Receiver Transducer Storage

11 © Boardworks Ltd 2003 Definitions ComponentFunction Encoder Decoder Modulator Transmitter Receiver Storage Transducer Amplifier Changes information into readable form Allows wave to carry impulses AM/FM Changes information to original form Stores information e.g. CD, DVD, tape Makes oscillations Collects information Changes information into electrical form or the other way round (microphone, speaker) Increases intensity of received waves

12 © Boardworks Ltd 2003 Which of the following is not a use of total internal reflection? A.Periscopes B.Endoscopes C.Fibre optic communication D.Mirrors

13 © Boardworks Ltd 2003 What does attenuation mean? A.Strengthening B.Increasing C.Larger D.Weakening


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