전자기파

전자기파

1. 전자기파의 발생기구에 따른 분류

•

이론)

• 가시광, x선, 감마선 : 원자 또는 핵 (양자물리학

이론)

p. 1109

Department of Physics

빛

전자기파; electromagnetic wave ^{p. 1108}

2. 방송파의 발생과 전파

EM fields at Plooking back toward LC oscillator

1

  LC

( ) q t

( )

 q t

( )

sin( ) q t  Q  t

0

0 2

( ) cos( ) sin(

( , ), ( , )

)

i t Q t

E r r

t

B t I

t



 









  

Department of Physics

3. 전자기파의 특성

• 전파속력:

• 전자기장 벡터

1. 방향:

2. 위상: E와 B는 조화진동하며 3. 진폭:

0 0

299, 792, 458

1 [m/s]

c ^   ^

( )

( ) / /

  



E B E B

전자기파

전파방향 는 횡파 전파방향

m m

( , )

( , ) sin( )

sin( );

/ =1/

E x t E kx t

B

B x t B kx t E c







m



m

=

=

•

->

•

Department of Physics

KBS1-Busan ~ 891kHz

KBS1-Busan 송신탑 높이~ 84m

890

8 3

3 10 m/s 891 10 Hz 337m c

  f  ^ 



/ 4 84 m

 

Department of Physics

Fa rada

: y

d B

E ds     

∮ 유도법칙

amplitu de ratio cos( )

cos( )

:

m

E x m B

m E

B t

k

k E kx t

B kx t

 c



 





 

 









Traveling EM Wave

1. ( ) -

2. ( )(

)

dE dB

dx dt

E B

x t

E dE h Eh hdE B h d

lhs

r hs x hdx

 

 

  

   

    



( , ) sin( )

B x t = B _m kx   t

전기장을 유도

p. 1112

0 0 ^d_dt^E

: Maxwell B ds      

∮ 유도법칙

0 0 0

0 0

0

0 0

1 1

( / )

c= 1

cos( )

c

wave spe

os( )

: ( e d )

m m

E B B

x m E

t m

k c

k B kx t

E kx t

     c

 



   





 

  

  





0 0 0 0

0 0 0 0

1. ( )

2. ( )( ) -

d dE

dt dt

dB dE

dx dt

B E

x t

B dB h Bh hdB E h d

lhs

rhs   x   hdx

 

 

     

 



  



자기장을 유도

( , ) sin( )

E x t = E _m kx   t

Speed of light is independent of the speed of an observer !!!

0 0

1 1

4 4

E E

k  k

 

  

0

0

1 1

4 4

M

M

k k



  

  

2

8

9 2

7

8.99 10 N m /C = 10 T m/[C/sec]

3 10 m/sec

E M

c k

k

 

 

 

Department of Physics

Mathematical Description of Travelling EM Waves

 

m

sin

E  E kx   t

 

m

sin

B  B kx   t

Wave Speed:

0 0

c 1

  

Wavenumber: 2

k 

 

Angular frequency:  2 

 

Vacuum Permittivity: 

Vacuum Permeability: 

All EM waves travel at c in vacuum

Magnitude Ratio:  

 

E t c B t 

Amplitude Ratio:

m

E c

B 

0

1

2

: Poynting vector / W

[ /m ] Energy time Power

S area ar a

S E

e



B

   

        

 



  

순간 순간

파원까지의 거리에 따른 세기 변화:

*

에너지 수송과 포인팅벡터

2 2

2 0 0

0 0

2

0 0

1

2 2

2

1 [ ]

2

2

B E

E c c B

S B

c

E e c E

= = =

m +

m m =

= m

p. 1116

2 2 2

0 0

1 1 1

sin ( )

m

2

I S E kx t E

c  c

 

   

Department of Physics

F p

t

 



운동량

power energy/time area area

U t

I A

 

  

, 세기

p U

c



 



=

p

U U

Fc

P F c

t

v t

t

 

 

  

  _운동량

(= ,일률)

U  IA t

  

EM waves have linear momentum as well as energy  light can exert pressure

Radiation Pressure,복사압력

U IA

p t

c c



   

 U

Radiation Pressure; 복사압력

2 rms 0

rad

rad

rad

total absorption;

:

for

R

* ADIATION PRESSURE (

for back

tota l r eflect io alo ng the p

) 1

2 at

n h

p

p I I S E

c p

F

c

c A

I

 



  

(

Please read pp. 1095-1097 by yourself.)

of an object thru radiati

momentum gain on absorption



U I A

p t

c c



   

 U

incident

S



p

incident

S

reflected

S



p

p. 1119

Department of Physics

EM waves have linear momentum as well as energy  light can exert pressure

Radiation Pressure,복사압력

Jet Propulsion Laboratory's

incredible video

Department of Physics

편광; Polarization

정의

p. 1121

코사인 규칙

편광기

검광기

Department of Physics

• 편광방향이 같은 경우 (모두 수직임)

• 편광방향이 직교하는 경우

반사(reflection)와 굴절(refraction) p. 1126

Department of Physics

Reflection Refraction

1

'

  

2

sin

sin

n   n 

Snell’s law

Department of Physics

For light going from n ₁ to n _2,

• n ₂ = n _{1 }  ₂ ⁼  ₁

• n ₂ > n _{1 }  ₂ ^<  ₁ , light bent towards normal

• n ₂ < n _{1 }  ₂ ^>  ₁ , light bent away from normal

2

sin

sin

n   n 

(dispersion)

Department of Physics

Chromatic Dispersion(색의 분산)

prism

or bad

lens

Chromatic dispersion can be good (e.g., used to analyze wavelength composition of light)

p. 1128 ^보기문제

Department of Physics

전반사; Total Reflection p. 1132

Department of Physics

1. Brewster Reflection

반사광선과 굴절광선이 90도를 이루면, 편광 방향이 입사평면에 대하여 나란한 빛은 전혀 반사되지 않는 현상. 이때 반사광의 편광 방향은 입사평면에 수직임.

반사를 통한 편광

(Brewster angle)