Subscribe to our educators newsletter

Email Address:
 
 
 

LOGIN

To access these free activities, you must log in to the Science World Resources site.


Colour and Light

Colour and Light

Chemistry - optics - eye - light - sunglasses - polarization - polarizer - rainbow - refraction - reflection - Kindergarten - wavelength - spectrum - chromatography - methylene blue - grade 2 - grade 4 - grade 5 - grade 8 - grade 9 - grade 11 - life science - earth and space science - physical science - processes and skills of science - wave motion - geometrical optics - physics

Rainbow Science!

Introduction

How are rainbows made? What makes grass green and jeans blue? How do sunglasses work? In this series of demonstrations and activities, students will explore how colours are created and understood by our brain.

This resource also demonstrates numerous ways of producing/revealing colour through chemical reactions, mixing different colours of light, mixing pigments, and chromatography. Students will develop an appreciation for the complexity of something we take for granted: colour.

Objectives

  • Name colour change as one of the possible outcomes of a chemical reaction.
  • Describe how different colours of light mix to give new colours.
  • Perform methods to separate colours.
  • Explain how polarizing filters work and their use in our daily lives.

Background

White light is made up of light with a range of different wavelengths, known as the visual spectrum. Every colour that we can see has a different wavelength and energy.

The back wall of the human eye (the retina) has two kinds of receptors for perceiving light: rods and cones. Rods respond to all wavelengths of the visible spectrum in low light conditions. They allow us to see objects in dim lighting conditions. Cones, on the other hand, respond to certain wavelengths, sending colour information to the brain. There are three different types of cone receptors for coloured light: one is most sensitive to red light, one to green light, and one to blue light. With these three colour receptors we are able to distinguish millions of colours. Cones are less sensitive than rods, requiring higher levels of light. This is why it is difficult to make out the colour of objects in low light conditions.

In order to see colours, there must be at least a little bit of light. White light is actually made of all colours, but the colours you see depend on the amount and colour of light being reflected (thrown back) or absorbed (taken in) by an object.

A red apple looks red because white light, either from light bulbs or from the Sun, hits the surface and all of the colours are absorbed except the red which is reflected back to your eye. Special cells in the back of your eye called cones get "excited" when they are hit by red light and send electrical signals to your brain.

Ordinarily, light waves vibrate in every plane and direction. Polarized light is light that is only vibrating in one plane. A polarizing lens permits only light vibrating in one plane to pass. Polarizing lenses are used on cameras and sunglasses to block the horizontal glare that is produced on reflective surfaces such as lakes.

A rainbow is formed when white light passes through rain droplets. Since different colours contained in white light have different wavelengths, they are refracted through the droplets at different angles, and the colours are separated. Artificial rainbows can be created in class by shining a light source through a clear glass of water — the same process occurs as in a rainbow seen outside.

Entire Lesson

These resources are free!
You must LOGIN to download the full lesson + activities. 

Other Resources

Science World Resources | Full Lesson | Glow Crazy
Science World at TELUS World of Science | Mitchell Odyssey Foundation Gallery: Eureka!
Science World | Online Games | Eureka! | Laser Beam
Ontario Science Centre | SciZone | Games | Computer Crayons
The Franklin Institute | Light and Color

 

Comments  

 
#1 Activity Delivery tips — Eugene Luk 2012-03-08 13:35
•Feeling Blue: dispose of the chemical solution after every session; the mixture cannot be re-used from day to day (it oxidizes and turns a pee-yellow colour). For a more exciting demo, mix ingredients during session in front of class (use warm/hot water tho to speed up reaction); you can have volunteer touch the bottom of container to feel exothermic heat given off by reaction.
•Colored Shadows: instead of supporting the flashlights on books, have volunteers hold the flashlights instead! Or alternatively, just place the coloured cellophane on an overhead projector.
•Chromatography Caper: alternatively, do this class activity in groups of 2. Each pair of students gets 1 marker; the ransom note will only match 1 pair's marker.
•Homemade Chalk: do this activity at session start - plaster/chalk needs time to fully dry! Probably best to have 1 facilitator in charge of scooping out paint powder (have students line up for this), while other facilitator(s) take turns making batches of plaster. Plaster of Paris solidifies EXTREMELY quickly, so you'll want to begin pouring as soon as you've finished mixing it! Remind students to stir all the way to bottom of their cups; also remind them to remove popsicle sticks after they're done stirring. Use plastic milk jugs (just cut open the tops) as pitchers for mixing/pouring plaster, and that way cleanup is simple - just dispose of the jugs after each session.