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ERIC Number: EJ1083223
Record Type: Journal
Publication Date: 2006-Dec
Pages: 2
Abstractor: As Provided
ISSN: ISSN-0031-921X
Excitation of Standing Waves by an Electric Toothbrush
Cros, Ana; Ferrer-Roca, Chantal
Physics Teacher, v44 n9 p578-579 Dec 2006
There are a number of ways of exciting standing waves in ropes and springs using non-commercial vibrators such as loudspeakers, jigsaws, motors, or a simple tuning fork, including the rhythmical shaking of a handheld Slinky. We have come up with a very simple and cheap way of exciting stationary waves in a string, which anyone, particularly children, can try at home. It consists of using an electric toothbrush to produce a regular sideways motion that can be easily transmitted to an elastic cord. Most suitable for this experiment is the kind of unit that has a metal rod protruding from the front (see Fig. 1, which shows our Braun Oral-B®) to which a brush is normally affixed. The ends of the cord are attached to stands. Elastic cords that come with some school notebooks work well for this experiment, but a longer cord allows the observation of a larger number of modes. The toothbrush unit is placed near one end of the cord, which is wrapped once around the rod. As the toothbrush vibrates at a fixed frequency, standing waves (see Fig. 2) may be tuned by changing the tension of the cord while keeping its length constant. We have found up to five harmonics with a 150-cm cord. The toothbrush can be connected to a small potentiometer to reduce the dc voltage and hence the frequency of the motor, allowing the tuning of the standing waves with a fixed tension.
American Association of Physics Teachers. One Physics Ellipse, College Park, MD 20740. Tel: 301-209-3300; Fax: 301-209-0845; e-mail:; Web site:
Publication Type: Journal Articles; Guides - Classroom - Teacher; Reports - Descriptive
Education Level: N/A
Audience: Teachers
Language: English
Sponsor: N/A
Authoring Institution: N/A
Grant or Contract Numbers: N/A