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-   -   Dispersion (http://physicshelpforum.com/light-optics/3423-dispersion.html)

quick.on.my.feet Nov 8th 2009 06:16 PM

Dispersion
 
A performer wears blue clothes on stage. How could you use spotlights to make them appear black? Is it possible to make them appear red? Explain.

So we need to shine something at them that makes them appear black. So would we shine blue/white light at them? cuz then blue would absorb blue, therefore every single colour will be absorbed making them appear black?

physicsquest Nov 8th 2009 09:37 PM

I think if you shine blue light it would appear black.

To make it look red, i think you should shine green light. With the blue removed , it should look red.

quick.on.my.feet Nov 9th 2009 08:47 PM

actually if you think about it, it has to be a blue object to reflect blue light. if you shone a white light, it would absorb all the other colours, and reflect blue. is it possible to shine a light that has blue absent in it?

physicsquest Nov 9th 2009 09:13 PM

It may be possible if you use say a red filter on white light. This would allow red to pass thru but not blue.

What you say about the object appearing blue because it reflects blue is true. Reflection is treated as absorption and re-emission , so blue is absorbed and re-emitted though why the other colours are not re-emitted beats me.

What we actually see must have something to do with the primary-secondary colour stuff which i can never remember.

I remember to have seen writing in red ink look black in red light.

quick.on.my.feet Nov 9th 2009 09:27 PM

Colours in optics is really messed up haha.
thanks =]


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