23 Electromagnetic Waves. Principle Faraday’s law: time-varying B-field creates E-field (emf)...
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Transcript of 23 Electromagnetic Waves. Principle Faraday’s law: time-varying B-field creates E-field (emf)...
Principle
Faraday’s law: time-varying B-field creates E-field (emf)Maxwell: time-varying E-field generates B-field (emf)
EM waves were PREDICTED by J.C. Maxwell in 1865. Light is part of the EM wave
Heitz first detected the EM waves in 1887 after Maxwell died (1879).
Another great prediction(s) was made by Einstein from his General Relativity.
James C MaxwellBritish Scientist(1831 – 1879)
Heinrich R HertzGerman physicist(1857 –1894)
Properties of EM Waves
1. Transverse Wave; Both E & B perpendicular to propagation, k. E, B and k follow the right-hand rule
2. EM waves can be created and travel in vacuum (no medium required) with unchanging speed c
3. E & B are in phase and E= cB
(in vacuum)
smc /1000.31 8
00
v = f
Energy in EM Waves
cutA
tuAc
tA
Vu
t
U
AS
uuEu
Ec
EB
BEuuu
BE
BE
1
)(
2
1
2
1
20
00
20
20
S: energy per unit area per unit time or power per unit area and the average value, Sav called intensity, I.
Index of Refraction & Snell’s LawNormal
Incident
Reflection
Refraction
a r
b
ra
bbaa nnv
cn
sinsin
Angles respect to normal lineAll the rays in same plane
nanb
Reflection & Refraction: Animations
Animation of Refraction (rays)
Animation of Refraction (waves)