Why is it that when I’m using my electric toothbrush, and watching TV at the same time, that the picture goes all shaky?
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 it’s scanned at a certain frequency (25Hz), so everything else would not appear wobbly!