Lens, Tiny Bulbs and Cloth Give the Wavelength of Light

Michael J. Moloney

Rose-Hulman Institute of Technology

(This talk is an adaptation and refinement of 'Homemade Interference', TPT November 1999 by the same author).

Figure 1. Two light bulbs hot-glued to a battery case with a pair of 1.5-v bulbs installed. A cloth sample has been stapled into a ready-mount.

Fig. 2. The light bulbs lighted, and a cloth sample stapled into a ready-mount.

Fig 2' . Suggestions for constructing the cloth grating mount.

Fig. 3. Determining the cloth spacing using a lens (done ahead of the class experiment).

Figure 3. Geometry for calculating the wavelength of light from simple measurements. A student starts by lining up with the bulbs, then moves to his or her left until the pattern of 'dots' is shifted over by one. The light wavelength is d sin theta, where d is the cloth grating spacing.

Figure 4. Details of wavelength calculation.

Some candid pictures of students measuring in the lab.

The student results for the wavelength of light.