Chapter 7--Atoms & Light

The Speed of light is a constant, it is always moving at 3x10^8 m/s. It makes no 
	difference if the source of the light is moving.
	This seemingly innocent statement means that our whole concept 
	of time ticking away at the same rate regardless of speed is no longer correct.

Mass is a form of energy--You can transform it to other forms of energy--like radiation.
	Is the total energy conserved in this process?   you better get this right.

Electrons in Atoms can be tightly bound or more loosely bound.  The amount of binding
	has an energy associated with it.  When the electron becomes more or less bound
	there is a change in energy.  Where did this energy come from (in the case of a 
	loosening of the bind) or where did the energy go (in the case of a tightening of the bind)?

Electromagnetic Radiation

 Light is Massless-- 

 The Energy of a single "particle" of light (photon) is proportional to its frequency.
	In the graph below Energy is given in Electron Volts
	1 Electron Volt = 1.6x10^-19 Joules  ---- does that number look familiar?

 Wave-Particle Duality of Nature--both light &  things with mass (i.e. electrons) sometimes
	behave like waves (which in a sense are spread out), and sometimes they act like 
	particles (which are well localized in space.)  See demo description below.






Demo: 

Shine a laser through a slit and look at the pattern the light makes upon  the wall. 
Instead of just one bright band of light directly behind the slit opening, you were supposed to
see a more spread-out pattern of alternating bright and dark bands.  
This indicates that the light is undergoing diffraction as it passes through the slit.  
Meaning that the light is behaving like a wave.  

Think of an example where light behaves like a particle (photons).

If you pass a beam of electrons through a slit, they too will produce a diffraction pattern--
meaning that even electrons can act like a wave.   WAVE-PARTICLE DUALITY of nature.
(see pages 215-216)