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 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 Maxwell British Scientist (1831 – 1879) Heinrich R Hertz German 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) v = f

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, S av 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 Normal Incident Reflection Refraction aa rr bb Angles respect to normal line All the rays in same plane nanbnanb

Experience: Driving & Reflections

Value of Refractive Index Air

Total Internal Reflection Critical angle: when  b = 90 o,  a =  c = sin -1 (n a /n b ) 90 cc

Dispersion: n= n( )

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 Correct Points Number of Students Your grade =points/16x100%