23 Electromagnetic Waves Principle Faradays law timevarying Bfield
23 Electromagnetic Waves
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) Heinrich R Hertz was made by Einstein from his German physicist General Relativity. (1857 – 1894) James C Maxwell British Scientist (1831 – 1879)
Properties of EM Waves 1. Transverse Wave; Both E & B perpendicular to propagation, k. E, B and k follow the righthand 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= c. B (in vacuum) v = lf
EM Spectrum
Images Taken in Different EM Wave Regions
Sinusoidal Waves
Energy in EM Waves S: energy per unit area per unit time or power per unit area and the average value, Sav called intensity, I.
Radiation Pressure
Nature of Light: Wave-Particle Duality
Wave Fronts Geometric optics & Physical Optics Rays & Waves
Reflection & Refraction
Index of Refraction & Snell’s Law Incident Normal qa qr Reflection na nb qb Refraction Angles respect to normal line All the rays in same plane
Experience: Driving & Reflections
Value of Refractive Index Air 1. 0003
Total Internal Reflection Critical angle: when qb = 90 o, qa = qc = sin-1(na/nb) 90 qc
Dispersion: n= n(l)
Polarization Linear polarization Circular polarization (left)
Mirage, Blue Sky, & Traffic Lights
Summary: EM Waves, Speed & Spectrum
Sinusoidal Waves and Energy
Nature of Light
Reflection & Refraction Total Internal Reflection:
Reflection & Refraction: Animations Animation of Refraction (rays) Animation of Refraction (waves)
Dispersion
Polarization
Homework Ch 23 Problems: 3, 6, 13, 20, 26, 38, 45, and 49
Test III Score Distribution 8 Your grade =points/16 x 100% 7 Number of Students 6 5 4 3 2 1 0 1 2 3 4 5 6 7 8 9 10 11 Correct Points 12 13 14 15 16 17
- Slides: 27
