## Wave bye-bye to your sanity…

Paradoxes are fun – if you understand them. Watching others attempt to reconcile the conflict between the irreconcilable is amusing. For example:

The following sentence is false.

The previous statement is true.

Which of these statements are correct? If your head is beginning to hurt, then you had better go and buy a very large box of panadol, because you are going to need it during the next unit of work. We are beginning your investigation into the properties of light, and it only gets weirder (and more paradoxical) the further in you get. The truth of the matter is that physicists don’t really know (absolutely) what light is. Scientists rely on a set of models (models are ways to explain why light behaves the way it does), but the porblem is that light doesn’t play nice. Certain models explain some behaviours, but not others. In fact, no one model explains all of the properties of light. Over the course of the next unit, we will look at two models:

1. Ray Model
2. Wave Model

The Ray Model is the simplest, but we still use it for the simplicity in explaining things like reflection and refraction. I have previously written a post about this on this blog, here. However, in order to explain some more complicated phenomena, we need to use the Wave Model, which is the topic of this post. (in year 12, you will study the particle model, and for those of you with a masochistic streak (You know who you are…), check this out as an introduction to the Quantum Electrodynamic Model (what the bleep!) (ps. don’t watch the rest of this “documentary” – it is a pile of conspiracy-minded bovine excrement encrusted with credulous delusional pseudoscience).

A wave is defined as followes:

Wave: an periodical (regular) oscillation (disturbance) which travels through a medium, transferring energy from one location to another.

This means that a (physical/mechanical) wave is exactly what you think of when you see an ocean wave – a “bump” (this is the wave crest) in the waterÂ  (this is the medium) that travels in a direction, and gives energy to what it hits. Physical waves (i.e. waves that causes visible “bumps” in what they travel through) come in two main types: Transeverse and Longitudinal (there are more, but that will do for today (ok, if interested, you can start with torsional, shear and surface)). Transverse waves have the bump (“pulse”) perpendicular to the directions of travel (propagation), like this:

Longitudinal waves have their pulses parallel to the direction of propagation, like this:

This is summarised in the following video:

A pair of powerpoints that provide good information:

OK, now some sources of good supplementary information:

1. Classroom Physics: A great, detailed website. This should be your first site to visit! (link)
2. Zonaland: This is also good; not so pretty, but very well organised. (link)
3. Educational Electronics: This is OK, but focusses more on sound. (link)
4. Antonine Education: This is also good, but goes a bit further than we do this year (link)
5. Science-Class: some good stuff here too, but a bit simple. (link)

OK, and for the studious amongst you, remember that you must have finished the “What is Colour” task that was assigned last term. This worksheet has to be completed by Lesson 1, Week 2 so get cracking!

See you in Class!

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### 13 Comments on “Wave bye-bye to your sanity…”

1. Patrick Says:

how significant would it be if someone were to create just a single model that could explain all the properties of light?

• CyberChalky Says:

Nobel Prize worthy – if a single model was able to explain all aspects of the behaviour of light, we would be significantly advanced in our ability to build/engineer technology that would allows us to manipulate/control/create E-M phenomena – e.g. lightsabers! Yay!

2. Patrick Says:

well, could it be POSSIBLE that light is somehow some from of exotic matter? that we, at the moment can’t discover?

• CyberChalky Says:

Patrick,

You can do better than this! The statement that you are making here is a form of logical fallacy called “argument from ignorance” i.e. because we don’t know what something is, it could be anything. Furthermore, appeals to advanced scientific principles, such as exotic matter or quantum physics as an explanation for unexplained phenomena are an unhealthy mental habit to adopt. This is not to say that your “possibility” is incorrect, but that without evidence, making such an assumption does not further our understanding. If you want to get into what light is, I advise you to check out a primer on Quantum Electrodynamics – here is one possibility:
http://www.allthingsscience.com/video/752/Quantum-Electrodynamics

MrG.

3. Locky Says:

I yelled at my computer screen when the particle model video decided to tell me that a single particle would split into two (and one. and none) and interfere with itself. That’s very cool.

Now to, you know. Learn the stuff that will actually be on the exam.

4. Loughlin Says:

It’s possible to separate different wavelengths of light. Is it possible to change the wavelength of a wave for more than just a couple of superpositions? Can you change a pure red wave into a purple one?

• Loughlin Says:

Superpositions change amplitude not frequency. Is it possible to change frequency though?

• CyberChalky Says:

Ever heard of FM radio? FM stands for Frequency modulation – changing the frequency of a carrier wave to transmit information.

5. Loughlin Says:

Hey Sir.
I’m having a little problem with using Huygen’s principle to explain how a some light is reflected from the surface of a glass prism even as most passes through.

To me Huygen’s explains that a light “wave” is made up of little wavelets, and that the wavefront can be treated like rays. Where am I going wrong?

• CyberChalky Says:

If you ever figure out how Huyghens principle does relate to partial reflection/ transmission, we’ll be calling the Turpin Principle.

6. […] Light & Waves: Colour, Wave basics , Diffraction, Refraction, Wave interactions, Wave […]

7. […] on this blog about light – they have a *lot* of useful resources. Here are the links (1, 2, 3, 4, […]

8. […] 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 […]