S(light)ly confusing…

In our studies of light so far, we have review the basic ideas of light transmission, including the ray and wave models (link to a prior post on this topic here. READ IT!), and the ways light traveling as a wave can create interference patterns, and the amazing interactions of diffraction (link to a prior post here. READ IT NOW!).

You need to understand how diffraction works, and to help you with your preparation for your outcome, here is a simulation that will help you explore diffraction phenomena – you must take your time to explore how the factors of wavelength (colour), slit width, slit separation and distance from screen interact to affect “fringe width” – the distance between maxima on the projection screen. You may wish to use your explorations in the simulation to augment and clarify your notes on your summary pages. Remember that you may not include general points of theory or examples unconnected to the context provided on those sheets (Pages from Outcome.)

The next part of light gets confusing. You may remember that I showed you the video linked in the first post above, the Dr.Quantum section of “What the Bleep do we know”. But as amazing as it seems that light has different natures depending on what it is doing, more interesting yet is how we discovered the dual nature of light.

To understand this story, we need to follow the story of Blackbody radiation and the Ultraviolet Catastrophe – this link goes to a playlist which goes into some detail. Note that you are not required to be able to explain this history (unlike you were required to explain Michaelson-Morley), but understanding it will help with your comprehension of other issues. In short, the Ultraviolet Catastrophe was another thought experiment (and later real experiment) which demonstrated that the Wave Model of light must be incorrect – but theoreticians at the time had nothing as effective a theory to replace it with… (arguments had long been running, but the wave had seemed to be the victor…)

Fortunately, a guy called Einstein was around, and hey and a few mates (Dirac, Schroedinger, De Broglie, Planck, Bohr and a couple of other nobodies (do I need a “/sarc” here?)) worked out a replacement theory which is still tormenting physicists everywhere: Quantum Mechanics.

What we are studying next is some of the best evidence for the particle model – the Photoelectric effect:

And here is the simulation we will be using as part of our outcome preparation: LINK.

See you in class.


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