同济大学：《大学物理》课程教学资源（电子教案，英文版）第十九章 电磁波

Light waves

Light waves

Agenda today 1.The nature of light waves 2.Reflection and refraction 3.Polarization

Agenda today 1. The nature of light waves 2. Reflection and refraction 3. Polarization

The spectrum of electromagnetic waves Cell Phone (3KHz-300GHz) 围米 GA) pojejjul uoneipeJ uoneipe sKeJ-X microwaves 六www 10 102104105105100101210141016101810201021024 1028 KHZ MHz GHz FREQUENCY non-ionizing radiation lonizing radiation 2001 HowStutfWorks

The spectrum of electromagnetic waves

Wavelength of visible light(in vacuum) 400-760nm The flowers appear differently in UV light

Wavelength of visible light( in vacuum): 400--760 nm The flowers appear differently in UV light

What is light? Particle theory by I.Newton Wave theory by C.Huygens The experiment done by T.Young. Photoelectric effect

What is light? Particle theory by I.Newton. Wave theory by C.Huygens The experiment done by T.Young. Photoelectric effect

Generation of Radio Waves Accelerating charges produce electromagnetic waves

Generation of Radio Waves E + + + - - - + - - + - - - + + + Accelerating charges produce electromagnetic waves

米C2k Why are cell phone antennas so short?

Why are cell phone antennas so short?

Interrelated electric and magnetic fields traveling through space Electromagnetic waves travel through empty space All electromagnetic radiation travels at c=3 x 108 m/s in vacuum-the cosmic speed limit!

Electromagnetic Radiation • Interrelated electric and magnetic fields traveling through space • Electromagnetic waves travel through empty space All electromagnetic radiation travels at c=3 x 108 m/s in vacuum – the cosmic speed limit!

For plane electromagnetic waves travel in x direction: By Maxwell's equations: E aB Wavefronts Ray (a) Bx 8t aB E -8 Bxc 8t E () 82E B Electric- -Magnetic 8t2 component component

For plane electromagnetic waves travel in x direction: By Maxwell’s equations:

Compared with the wave equation of mechanical waves Let: E=E sin(kx-@t) B=B sin(kx-@t) OE aB m Bx 8t B Hm

Compared with the wave equation of mechanical waves Let: