Activities > For Ages 10 and Up

Colors and Spectroscopy

Do you know why we can see a rainbow in a sunny rainy day? Do you know what a color is?

Materials

Transmission diffraction grating from the Optical Society (OSA) Optics Suitcase and old CD
Color filters (green, blue, red)
Torch
Light bulb
Compact fluorescent lamp
Mercury-vapor lamp
LEDs (different colors)
Candle flame
Green apple

Directions

Do you know why we can see a rainbow in a sunny rainy day? Do you know what is a color? Have you ever thought are white and black colors? Have you ever wondered what color will a green apple appear to be when viewed through red and green glasses respectively? Can you tell what colors are produced by a light source by just looking at the light? What kind of instrument do you need to separate the colors to see them? If not, this activity will bring you closer to the answers. 
 

light.jpg
 
Turn on a torch and direct the CD towards it. Change the position of CD for so long as the spectrum of different colors will appear on it. Repeat it for different light sources. Do spectrums differ for various light sources?
Turn on a torch and look on it through diffraction grating placed in the front of your eyes. Can you see a light spectrum? Does it look the same as previously seen using CD? Now, place green, blue, red filters respectively just behind a diffraction grating and look at a torch light again. Do you see any difference?
Now check how the green apple appears if you look at it with various filters placed in front of your eyes.
 

Explanation

Visible light is the only electromagnetic energy that the human eye can see. White visible light is composed of a group of electromagnetic wavelengths that make up the colors we see. Each color within the visible light spectrum has its own individual wavelength and frequency. For example, red light has the longest waves and violet light has the shortest waves. Like a prism, the diffraction grating and CD can be used to break light into a spectrum. But why different object appear a certain color? Well, it happens because they absorb (or subtract) all the visible light colors except the color that is reflected back to your eye.