Question

Experiment to find ways to make rainbows.
a) Insert at least one setup where light passing through a prism gives a rainbow and describe why a rainbow is formed.
b) Explain why only some types of light will yield rainbows.

Explanation:

a) To get a rainbow from a prism arrangement, we will need

1. A triangular prism
2. A black cardboard box
3. A source of white light (light from the window will suffice)
4. A pocket knife

First, you cut a slit in one end of the cardboard with the pen knife.

Next you open up a space on top of the cardboard through which you can observe the experiment and its result.

Next, you place the triangular prism with its slant face facing the the cut slit.

Finally, position the slit to face the light from the open window, and adjust the prism till the projected bands of colored light (rainbow) is very much obvious on the other end of the box, opposite the slit.

b) For a light to yield rainbow, it most be composed of different component colors of light. The colors of light is due to the difference in wavelength, and dispersion is due to the different in the wavelengths of the component light. So to get rainbow from a light source, the light must not be monochromatic. This means that only light composed of component light of different colors can produce rainbow. Light from the sun for example is composed of 7 distinct colors of light, and white light can be created with just three colors; blue, green, and red light.