Electromagnetic waves

Transcription

1 Eletromagneti waves He predited eletromagneti wave propagation James Clerk Maxwell ( )

2 Eletromagneti waves He predited eletromagneti wave propagation A singular theoretial ahievement of the 19 th entury James Clerk Maxwell ( )

3 Eletromagneti waves He predited eletromagneti wave propagation A singular theoretial ahievement of the 19 th entury It was know that time hanging B indued E (araday s law) James Clerk Maxwell ( )

4 Eletromagneti waves He predited eletromagneti wave propagation A singular theoretial ahievement of the 19 th entury It was know that time hanging B indued E (araday s law) Another symmetry argument James Clerk Maxwell ( )

5 Eletromagneti waves He predited eletromagneti wave propagation A singular theoretial ahievement of the 19 th entury It was know that time hanging B indued E (araday s law) Another symmetry argument Maxwell hypothesized: a time hanging E must indue B James Clerk Maxwell ( )

6 Eletromagneti waves He predited eletromagneti wave propagation A singular theoretial ahievement of the 19 th entury It was know that time hanging B indued E (araday s law) Another symmetry argument Maxwell hypothesized: a time hanging E must indue B James Clerk Maxwell ( ) and there was light

7 Heinrih Hertz ( ) in 1887 generated & deteted eletromagneti (EM) waves in lab

8 Heinrih Hertz ( ) in 1887 generated & deteted eletromagneti (EM) waves in lab Hertz apparatus

9 Heinrih Hertz ( ) in 1887 generated & deteted eletromagneti (EM) waves in lab Hertz apparatus L

10 Heinrih Hertz ( ) in 1887 generated & deteted eletromagneti (EM) waves in lab Hertz apparatus L C

11 Heinrih Hertz ( ) in 1887 generated & deteted eletromagneti (EM) waves in lab Hertz apparatus L C L* C*

12 Heinrih Hertz ( ) in 1887 generated & deteted eletromagneti (EM) waves in lab Hertz apparatus L C f MHz L* C* f 0 π 1 LC π 1 * L C *

13 Heinrih Hertz ( ) in 1887 generated & deteted eletromagneti (EM) waves in lab Hertz apparatus EM wave

14 Heinrih Hertz ( ) in 1887 generated & deteted eletromagneti (EM) waves in lab Hertz apparatus EM wave EM waves are generated beause harges are aelerating

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19 Moving harges produe urrents whih in turn produe B

20 Moving harges produe urrents whih in turn produe B

21 Transverse wave E and B at right angles to eah other and both are transverse to wave propagation diretion

22 Transverse wave E and B at right angles to eah other and both are transverse to wave propagation diretion µ 1 0 ε 0

23 Transverse wave E and B at right angles to eah other and both are transverse to wave propagation diretion wavelength l µ 1 0 ε 0

24 Transverse wave E and B at right angles to eah other and both are transverse to wave propagation diretion wavelength l µ 1 0 ε 0 f λ

25 roperties of eletromagneti waves Speed m/s

26 roperties of eletromagneti waves Speed m/s Maxwell proved: E B

27 roperties of eletromagneti waves Speed m/s Maxwell proved: E B EM waves arry energy and linear momentum

28 roperties of eletromagneti waves Speed m/s Maxwell proved: E B EM waves arry energy and linear momentum Beause E and B fields store energy in them. In fat, energies stored in E & B fields are equal.

29 Let S intensity average rate at whih EM-wave energy passes through a unit area perpendiular to diretion of wave W/m.

30 Let S intensity average rate at whih EM-wave energy passes through a unit area perpendiular to diretion of wave W/m. S E B µ max 0 max ( ) E µ max 0 µ 0 ( B ) max

31 Let S intensity average rate at whih EM-wave energy passes through a unit area perpendiular to diretion of wave W/m. S E B µ max 0 max ( ) E µ max 0 µ 0 ( B ) max Radio station with total power : what is S at distane r from station?

32 Let S intensity average rate at whih EM-wave energy passes through a unit area perpendiular to diretion of wave W/m. S E B µ max 0 max ( ) E µ max 0 µ 0 ( B ) max Radio station with total power : what is S at distane r from station? S 4πr

33 Let S intensity average rate at whih EM-wave energy passes through a unit area perpendiular to diretion of wave W/m. S E B µ max 0 max ( ) E µ max 0 µ 0 ( B ) max Radio station with total power : what is S at distane r from station? S 4πr One you know S, you an find E max and B max

34 Sine the delivers at the surfae of the earth S ~1 kw/m, find E max and B max.

35 Sine the delivers at the surfae of the earth S ~1 kw/m, find E max and B max. ( ) E S max max µ 0 max 0 µ 0 µ ( E ) S E S

36 Sine the delivers at the surfae of the earth S ~1 kw/m, find E max and B max. ( ) E S max max µ 0 max 0 µ 0 µ ( E ) S E S

37 Sine the delivers at the surfae of the earth S ~1 kw/m, find E max and B max. ( ) E S max max µ 0 max 0 µ 0 µ ( E ) S E S

38 Sine the delivers at the surfae of the earth S ~1 kw/m, find E max and B max. ( ) E S max max µ 0 max 0 µ 0 µ E max 870 V / m ( E ) S E S

39 Sine the delivers at the surfae of the earth S ~1 kw/m, find E max and B max. ( ) E S max max µ 0 max 0 µ 0 µ ( E ) S E S E max 870 V / m B max E max T

40 Deteting EM waves Deteting E-field part E

41 Deteting EM waves Deteting E-field part E Antenna C L

42 Deteting EM waves Deteting E-field part E Antenna C L Deteting B-field part B

43 Deteting EM waves Deteting E-field part E Antenna C L Deteting B-field part Loop antenna B C L

44 Deteting EM waves Deteting E-field part E Antenna C L Deteting B-field part Loop antenna B C L Indued emf due to hanging B-flux in antenna

45 Linear momentum arried by EM wave light pressure (N/m )

46 Linear momentum arried by EM wave light pressure (N/m ) Complete absorption: S

47 Linear momentum arried by EM wave light pressure (N/m ) m N s m m s m N s m m s J m / s m W / S Complete absorption: S

48 Linear momentum arried by EM wave light pressure (N/m ) m N s m m s m N s m m s J m / s m W / S Complete absorption: S Complete refletion: S

49 Linear momentum arried by EM wave light pressure (N/m ) Complete absorption: S S W / m m / s J s m m s N m s m m s N m Complete refletion: S Light bouning off mirror imparts more momentum to mirror

50 The effet of light pressure on dust in our solar system (Applying hysis 1., p. 67)

51 The effet of light pressure on dust in our solar system (Applying hysis 1., p. 67) Sun dust partile of radius r and mass m in orbit around R

52 The effet of light pressure on dust in our solar system (Applying hysis 1., p. 67) Sun dust partile of radius r and mass m in orbit around R light πr 4πR πr S πr 4R r

53 The effet of light pressure on dust in our solar system (Applying hysis 1., p. 67) Sun R dust partile of radius r and mass m in orbit around light πr 4πR Light not refleted πr S πr 4R r

54 The effet of light pressure on dust in our solar system (Applying hysis 1., p. 67) Sun R dust partile of radius r and mass m in orbit around light πr 4πR Light not refleted πr S πr 4R r

55 The effet of light pressure on dust in our solar system (Applying hysis 1., p. 67) Sun R Light output power of dust partile of radius r and mass m in orbit around light πr 4πR Light not refleted πr S πr 4R r

56 The effet of light pressure on dust in our solar system (Applying hysis 1., p. 67) Sun R Light output power of dust partile of radius r and mass m in orbit around light πr 4πR Light not refleted πr S πr 4R r grav G M R m G M ρ R 4 3 πr 3

57 The effet of light pressure on dust in our solar system (Applying hysis 1., p. 67) Sun R Light output power of dust partile of radius r and mass m in orbit around light πr 4πR Light not refleted πr S πr 4R r grav G M R m G M ρ R 4 3 πr 3

58 The effet of light pressure on dust in our solar system (Applying hysis 1., p. 67) Sun R Light output power of dust partile of radius r and mass m in orbit around light πr 4πR Light not refleted πr S πr 4R r grav 4 3 G M ρ πr G M m 3 density of R R dust partile

59 Compute light / grav ratio

60 Compute light / grav ratio light 4R r grav G M ρ R 4 3 πr 3

61 4R r light 3 grav R r 3 4 M G π ρ ρ π ρπ r 1 16 GM 3 3R r 4 GM 4R r 3 grav light Compute light / grav ratio

62 4R r light 3 grav R r 3 4 M G π ρ ρ π ρπ r 1 16 GM 3 3R r 4 GM 4R r 3 grav light Compute light / grav ratio

63 4R r light 3 grav R r 3 4 M G π ρ ρ π ρπ r 1 16 GM 3 3R r 4 GM 4R r 3 grav light Compute light / grav ratio

64 4R r light 3 grav R r 3 4 M G π ρ ρ π ρπ r 1 16 GM 3 3R r 4 GM 4R r 3 grav light kg m N G W; kg; 10.0 M Compute light / grav ratio

65 4R r light 3 grav R r 3 4 M G π ρ ρ π ρπ r 1 16 GM 3 3R r 4 GM 4R r 3 grav light kg m N G W; kg; 10.0 M 3 kg/m g/ 3 ρ or dust partile Compute light / grav ratio

66 4R r light 3 grav R r 3 4 M G π ρ ρ π ρπ r 1 16 GM 3 3R r 4 GM 4R r 3 grav light kg m N G W; kg; 10.0 M µ µ m) r( m 0.18 grav light Compute light / grav ratio 3 kg/m g/ 3 ρ or dust partile

67 Compute light / grav ratio light 4R r grav G M ρ R 4 3 πr 3 light grav GM r 4R 4ρπr 3 3R 3 GM 16πρ 1 r M or dust partile kg; W; G ρ 3 g/ kg/m 3 11 N m kg light grav 0.18 µ m r( µ m) or r < 0.18 mm, dust partile will pushed out of solar system!