======Colour Subtraction with Filters======


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**Materials: **{{$demo.materials_description}}\\
**Difficulty: **{{$demo.difficulty_description}}\\
**Safety: **{{$demo.safety_description}}\\
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**Categories:** {{$demo.categories}}
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**Alternative titles:** Light Absorption and Transmission
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====Summary====                   
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====Procedure====  
  - Shine white light through a colored filter (such as red, green, or blue cellophane). Observe which colors pass through and which are blocked.  
  - Try secondary filters (cyan, magenta, yellow) and notice that they transmit two primary colors while absorbing the third.  
  - Place objects of different colors behind the filters to see how their appearance changes.  
  - Direct white light onto colored surfaces and observe which colors are reflected and which are absorbed.  
  - Compare results with white and black surfaces: white reflects all colors, while black absorbs all colors.



====Links==== 
Colour Filter Demonstration - Physics with Simon Poliakoff: 
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📄 Colour subtraction, absorption and reflection - BBC Bitesize: [[https://www.bbc.co.uk/bitesize/articles/z6mpywx#zwwmh4jv]]\\

====Variations====
  * Use 3D glasses or sweet wrappers as inexpensive filters.  
  * Shine different colored lights (red, green, blue, cyan, magenta, yellow) onto objects and compare their appearance.  
  * Mix filters together (for example, red + blue cellophane) to explore subtractive color mixing.


====Safety Precautions====
  * Do not look directly into strong light sources.  
  * Use LED lamps or stage lights rather than lasers to avoid eye damage.  
  * Supervise children when working with electrical light sources.




====Questions to Consider====
  * Why does a red filter only transmit red light? (Because it absorbs green and blue light, subtracting them from the white light.)  
  * Why does a cyan filter appear cyan under white light? (Because it transmits green and blue light, absorbing red.)  
  * Why does a surface sometimes look black under colored light? (Because the surface absorbs the available wavelengths and reflects none back to the eye.)  
  * How is color subtraction different from color addition? (Addition mixes light sources to make new colors, while subtraction removes wavelengths through filtering or absorption.)