Wavelength

PERCEIVING COLOURS
Properties of light

Create a visual demonstration for light’s wavelengths with a slinky!

Details:

• Ages: 5-99

• Time: 20 minutes

• Learning Outcome: Use a slinky or a skipping rope to develop your own visualization for the concept of wavelength. As the speed of the moving slinky or skipping rope varies, you will discover the relationship between energy and wavelength.

• Colour Concepts: The relationship between wavelength and energy can be easily seen from looking at the electromagnetic waves of the electromagnetic spectrum. This exercise allows you to create a visual demonstration of the inverse relationship between wavelength and energy. It will clearly show that the shorter wavelengths of the electromagnetic spectrum correspond to the higher energy portions of the electromagnetic spectrum. Further, it will show that the longer wavelengths of the electromagnetic spectrum correspond to the lower energy portions of the electromagnetic spectrum.

Materials:

• Slinky (Figure 1) or skipping rope

Instructions:

• Have a friend hold one end of the slinky still.

• Holding the other end of the slinky, walk away from your friend until the slinky is in an approximately straight line (or has only a bit of a downward dip).

• Move your hand up and down once. Notice how a wave travels through the slinky.

• Move your hand continuously up and down. Find the rhythm of smoothly moving your hand up and down, so you create a wave that looks like Figure 2.

• If you move your hand up and down at a faster rhythm, you will be able to create a wave that looks like Figure 3.

• If you move your hand even faster, you will be able to create a wave that looks like Figure 4. As you move your hand faster and faster, you are putting more energy into the wave you create.

What’s going on?

In Figure 2, the solid line demonstrates half a wavelength, Figure 3 demonstrates one full wavelength and Figure 4 demonstrates 1.5 wavelengths. As more energy is put into creating a wave in the slinky, the peaks of the wavelengths get closer together. This exercise demonstrates the idea that higher energy parts of the electromagnetic spectrum correspond to shorter wavelengths (i.e. the peaks are closer together).

More to explore:

To demonstrate the polarization of the light wave, you can move your hand back and forth in different orientations. When you move your hand up and down, the wave travels perpendicular to the ground. When you move your hand side to side, the wave travels parallel to the ground. These demonstrate two different polarizations. You can move your hand back and forth diagonally to demonstrate another polarization.

Find out more:

• See What is the relationship between light, wavelength and colour?

• See this NASA video and reference for a description of the electromagnetic spectrum.