Lecture 36

Readings

http://umdberg.pbworks.com/w/page/52985393/Electromagnetic%20radiation%20and%20Maxwell%27s%20rainbow

Wave Model of Light

• What is moving?

  • For strings , it's the bits of mass on string :

    

  • For Sound , it's the air molecule :

  

  • For light ? It's the electric and magnetic field amplitude :

    • As time goes on , the "max up" location travels to the right

• So light is this electric field wave ( and magnetic field wave at the same time )

• Is there any matter involved? Is any physical thing with matter oscillating?

  • No. No matter needed. EM waves can travel through vacuum.

    • Thats how we see stars

  • But if the EM wave comes across a charged particle, the electric field in the wave will make the charged particle oscillate up and down

• Where is the photon?

  • It can't be visualized easily in this view. It takes quantum mechanics, and more wave math to describe it

  

• Still use wave equations though

  • $E=E_0\ast sin((k\ast x)-(\omega \ast t))$$E = E_0 * sin((k * x)-(\omega *t))$
  • $E$$E$ is the electric field amplitude
  • $E_0$$E_0$ is the maximum electric field amplitude

• In vacuum

  • Wave velocity = $v=c=\frac{\omega }{k}=\lambda \ast f$$v = c = \frac{\omega}{k} = \lambda *f$

  • $c$$c$ is the speed of light = $\frac{3\ast {10}^{8}meters}{1second}$$\frac{3 * 10^{8}\ meters}{1\ second}$

  • Other wavelengths all have this same speed , same electric field oscillations ( even though some are called rays ) :

    • Gamma rays
    • X-Rays
    • Ultraviolet
    • Light
    • Infrared
    • Radio

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