Difficulty: difficulty-1difficulty-2difficulty-2difficulty-2difficulty-2

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Kit contents:

red, blue and green LEDs (LED = light emitting diode)
3 button batteries
3 stands to hold each battery + LED pair

Prepare your light source:
  1. Assemble your stands by removing the paper or plastic adhesive film and slotting the foot into the stand.
  2. Place a battery so that the two legs of your LED straddle it, with the long leg (positive pin, anode) on the battery top (positive terminal). You can use tape to hold it.
  3. Slot the battery and LED into your stand.

 

Making coloured shadows:  In a dark room, arrange your red, green and blue lights so that they all shine together onto one spot on a white piece of paper or a white wall. What colour do the coloured lights make when combined?

Now experiment with what happens when you put an object (like a pencil or small toy) in front of the LEDs so that a shadow is cast onto your screen? What does your shadow look like? Why do you think it is so colourful?  Move the object around and watch how the shadows change. Try changing the arrangement of the LEDs – change how far away from the screen they are, their angles to the screen. How does this change your shadows?  What can YOU think of to try? What do you observe?

What is happening?  Red, green and blue are the primary colours of light. When they are mixed together, white light is produced! We can get 7 different colours from just 3 lights!

Blue, green and red are easy – and we know what all three mixed together does. How do we get yellow? magenta (bright pink)? cyan (bright light blue)?  Hint: try blocking one of your lights at a time and see what the other two make when combined on your screen.

Why do you see such crazy coloured shadows? When an object blocks the light beam from one of your LEDs, its shadow removes that colour from the white light. You are left with the colour from the other two lights. Because the beams of light are coming to the screen at different angles, you see crazy coloured shadows!

More! Explore and put in context:  What are the primary colours of paint? What do you get when you mix these paint colours? How is this different from your observations on light? What do you think?

 Keen to know more:  Try looking up colour wheels, additive colour mixing and subtractive colour mixing.  And do your own experiments!!  Never stop asking and answering questions!!

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