Colouring outside the lines…

VLspectrum  Colours are amazing – a world without colour would be truly uninspiring. We even describe something that is depressing or unimpressive “grey” or “colourless”. But what is colour, scientifically speaking? Well, for a start, red is not made up of red waves – colour is a response of the human eye to a specific range of frequencies. The part of the electromagnetic spectrum that can be perceived by the human eye as colour is called the visible light spectrum:EMspectrum

Colours themselves are interesting, but what happens when they interact with each other is even more interesting. Colours can either be added (light from two different sources interact) or subtracted (light passes through a filter or reflects of a coloured surface).
                                           Additive Colours     Subtractive Colours                                         
The first picture (left) shows what happens when you add colours, the second (right) shows what happens when you subtact colours by allowing them to pass through a series of filters. Here is a link to a flash application to investigate colour addition – play with it and see what colours you can generate (can you make orange, for example?).
Here is a video showing how colours can interact:


And here is a second video showing a similar experiment

 Finally, here is an excellent documentary, in six parts, giving a great roundup of a lot of the physics and engineering behind light effects in the modern world. (Part 1, Part 2, Part 3, Part 4, Part 5, Part 6). Here are the board notes from our lesson, and here are the next section of class notes

Three more links:

  1. Colour Survey – Try it – you think you know what blue is, don’t you…
  2. Results from the Colour Survey: Only for the hardcore geeks amongst you.
  3. Java Applets on Colour – you are expected to use these. Get to it!

See you in class.

Explore posts in the same categories: Physics

9 Comments on “Colouring outside the lines…”

  1. Locky Says:

    Hey Sir, just a quick question on the nature of the refractive index of air changing due to temperature. The book is confusing when explaining whether it increases or decreases. Does this correspond to the molecular structures changing slightly based on temperature?

  2. Patrick Says:

    Sir im having problems with the colour and waves worksheet
    Q7) if a light beam has a wavelength of 410nm how long does it take for one wavelength to pass a point?

    i calculated the frequency, which is speed over wavelength and ended up with 7.31*10^14 Hz.

    then i put that figure into the T= 1/F formula, and got 1.36*10^-15 seconds

    what am i doing wrong? cause i feel like that is the wrong answer :S

    • CyberChalky Says:

      No, that’s right…
      You just did it the long way.

      Remember that T = 1/f, but f = c/wavelength, so then T = 1/c/wavelength or, T = wavelength/c

      one step instead of two!

  3. Patrick Says:

    Q9) if you are 2.45km from nearest mobile phone tower, how long would it take for the signal to go from your phone to the tower?

    because we are given a distance, and we are meant to find time, and because we use are dealing with a E.M wave, speed is c.

    we use t=d/c?
    or is there another way to do this?

    • CyberChalky Says:


      You need some confidence in your own problem-solving strategies; what you have suggested is perfectly correct. Furthermore, it is one step – one equation – there are other ways, but none are simpler. Keep up the good work.

  4. Patrick Says:

    sir, i was wondering where i can get the worksheet on waves and colour, as i can’;t seem to find it.

  5. Patrick Says:

    Sir i know this is a physics post, but the question i have is methods related, at the moment im doing tan graphs, to figure out the asymptotes the equation has K, as a constant yet i dont know what type of value im meant to sure in for K. :S

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

  7. […] We use three main models – Rays, Waves & Particles. This year, we focus on Rays & Waves, next year will be particles. There are a few posts on this blog about light – they have a *lot* of useful resources. Here are the links (1, 2, 3, 4, 5). […]

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