May 6 2005 web.mit.edu/8.02x/wwwQuiz 1 Quiz 2Quiz 3 Quiz 42004 Quiz Grades706870 65May 6 2005 web.mit.edu/8.02x/www2005 Quizzes68 72Quiz 1 Quiz 272Quiz 3Quiz 474May 6 2005 web.mit.edu/8.02x/wwwE.M. WaveMay 6 2005 web.mit.edu/8.02x/wwwE.M. WaveMay 6 2005 web.mit.edu/8.02x/wwwExperiment MWMW (Micro-Wave):Generate and detect Electromagnetic WavesMay 6 2005 web.mit.edu/8.02x/wwwMW Block Diagram Transmitter ~ LVPS/HVPS Receiver LVPS/AMP ~12V AC12V AC MMM B C C A Antenna 1 MW Resistors Capacitor Spark GapMay 6 2005 web.mit.edu/8.02x/wwwMW in Real Life Spark-GapTransmitter Receiver-Antenna ReflectorMay 6 2005 web.mit.edu/8.02x/wwwMW in Real Life LVPS/HVPS HV to Spark Gap from Transformer LVPS/AMP to MMM A C C B from Receiver-AntennaMay 6 2005 web.mit.edu/8.02x/wwwSpark-Gap Emitter 1M! Resistor to HVPSDipole Antenna (2 x 31mm) Spark-Gap (0.05mm) 1M! Resistor CapacitorMay 6 2005 web.mit.edu/8.02x/wwwReceiving Antenna Schottky DiodeDipole Antenna (2 x 31mm) 10mm Loop to AMP One Piece!May 6 2005 web.mit.edu/8.02x/wwwMaking wavesR (1M!)800VR (1M!)C (33pF)Spark-Gap (0.5mm)May 6 2005 web.mit.edu/8.02x/wwwMaking wavesR (1M!)800VR (1M!)C (33pF)Spark-Gap (0.5mm)Vgap (= VC)t" = RC ~ 0.15msIgaptCharge C across R~4.5M!Discharge Cacross GapMay 6 2005 web.mit.edu/8.02x/wwwMaking wavesIgaptAntenna has ‘L’ and ‘C’ (and ‘R’):Damped OscillatorEMF -’Ping’ every 0.15msEnergyMay 6 2005 web.mit.edu/8.02x/wwwMaking waves+Q-Q+Q-Q+Q-QtimePeriod T =#x/v = 4L/cFrequency f = c/4LLength LMay 6 2005 web.mit.edu/8.02x/wwwMaking waves+Q-Q+Q-Q+Q-QtimePeriod T =#x/v = 4L/cFrequency f = c/4LLength LE-FieldMay 6 2005 web.mit.edu/8.02x/wwwMay 6 2005 web.mit.edu/8.02x/wwwE.M. WaveAntenna determinesFrequency: f = c/4LPolarization: E || Antenna© 8.02TMay 6 2005 web.mit.edu/8.02x/wwwReceiverE-FieldAmplitudePropagation#V ~ EMay 6 2005 web.mit.edu/8.02x/wwwReceiverE-FieldEt#Vt#V(diode)tMay 6 2005 web.mit.edu/8.02x/wwwPolarizationMay 6 2005 web.mit.edu/8.02x/wwwPolarization• Polarization:– Oscillation of fields has well defined direction• Polarization only possible for transversewaves• In general, light (sun, lightbulb) isunpolarized– Superposition of waves with many differentorientations• Can be polarized using e.g. polarizer foilsMay 6 2005 web.mit.edu/8.02x/wwwInterference Reflector!?May 6 2005 web.mit.edu/8.02x/wwwSuperposition of wavesMay 6 2005 web.mit.edu/8.02x/wwwMicrowave interferenceMay 6 2005 web.mit.edu/8.02x/wwwMicrowave InterferenceMay 6 2005 web.mit.edu/8.02x/wwwInterference Metallic Reflector Antenna Wave from emitter Reflected wave D “Virtual Emitter” DMirror gives phase-shift of 180oNeed to get 360o total: 2*D + 1800 = $, e.g. D = 3/4$May 6 2005 web.mit.edu/8.02x/wwwExperiment MWYour experiment shows:Wave Nature of E.M. radiationTransverse polarizationSpeed c = ! * fMay 6 2005 web.mit.edu/8.02x/wwwMonday:The Nature of LightWhy is the sky blue during day...... and red at sunset?Santorini,
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