Science Questions

Electric toothbrshes and wobbly TVs

Sun, 22nd Jul 2007

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Question

Alexander asked:

Why is it that when Im using my electric toothbrush, and watching TV at the same time, that the picture goes all shaky?

Answer

Electric toothbrushes contain an electric motor which is made to turn by the electricity from the battery inducing a magnetic field. The motor contains a commutator and some brushes, which are usually made of carbon. As the motor rotates, it intermittently connects with the brushes, and this leads to an intermittent current which then makes a spark. This effectively means that your electric toothbrush generates radio waves across a wide range of frequencies, which will affect anything nearby that is sensitive to radio waves, such as your TV or your radio.

Another reason for what looks like a wobbly picture when watching TV and using an electric toothbrush is the vibrations caused to your skull and eyes.  This may only effect a TV because its scanned at a certain frequency (25Hz), so everything else would not appear wobbly!

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