Presentation on theme: "Waves: Total Internal Reflection and Communication"— Presentation transcript:
1 Waves: Total Internal Reflection and Communication Give the meaning of critical angleDescribe internal and total internal reflectionRecall and use the definition of refractive index n in terms of speedRecall and use the equation sin i /sin r = nDescribe the action of optical fibres particularly in medicine and communications technology
2 Total Internal Reflection Angle rRefracted rayAngle rAngle iIncident rayReflected rayAt 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 < cRefraction i = cCritical case i > cTotal 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…MaterialRefractive indexCritical angleGlassWaterDiamond1.542°1.3349°2.424°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.OpticalElectricalInformationAttenuationInterferenceCostCarry moreCarry lessLessMoreNoYesMoreLessHow is attenuation solved in optical and electrical fibres?Regenerators for electrical cablesRepeaters for optical fibres
8 Digital and analogueWhat 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?AnalogueExamples 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:ModulatorTransducerEncoderTransmitterAmplifierStorageDecoderReceiver
11 Definitions Component Function Encoder Decoder Modulator Transmitter ReceiverStorageTransducerAmplifierChanges information into readable formChanges information to original formAllows wave to carry impulses AM/FMMakes oscillationsCollects informationStores information e.g. CD, DVD, tapeChanges 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? PeriscopesEndoscopesFibre optic communicationMirrors
13 What does attenuation mean? StrengtheningIncreasingLargerWeakening