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Author Topic: Why does my electric toothbrush make my oven misbehave?  (Read 1804 times)

Offline thedoc

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Julie Bissell asked the Naked Scientists:
   
Our shower room is next to the kitchen, and one morning I wandered into the kitchen to check everything was OK while I was brushing my teeth with an electric toothbrush. I was startled to see that the LED figures telling the time on the microwave were dancing around crazily. As soon as I took the toothbrush off my teeth, the figures became steady. Toothbrush in; figures started to shake violently again. A bit of experimenting tells me that an electric toothbrush vibrating on my teeth makes no effect at all on any item I look at unless it is LED figures, like a radio alarm, microwave display, kitchen timer. These LED figures look like they are being shaken hard. What is going on?
 
Julie

What do you think?
« Last Edit: 21/06/2014 12:30:01 by _system »


 

Offline evan_au

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Re: Why does my electric toothbrush make my oven misbehave?
« Reply #1 on: 21/06/2014 12:57:41 »
The toothbrush vibrating your teeth shakes your eyes too.
Most stationary objects will just get a little blurry around the edges.

However, the LED display is continually flickering, a technique called "multiplexing" - this is normally invisible to the human eye. When the electric toothbrush shakes your eyes, the thin lines of the multiplexed LED segments appear at many different positions, at different times.

It may appear more dramatic if the toothbrush is vibrating at a multiple of the LED multiplexing frequency. Try it again when the batteries in the toothbrush have run down a bit, and see if it looks any different.
 

Offline peterloo

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Re: Why does my electric toothbrush make my oven misbehave?
« Reply #2 on: 20/09/2014 03:18:53 »
The frequency of your eyes vibrate by newbielink:http://www.bestsellingreviews.com/Personal-Care/Electric-Toothbrush/ [nonactive] and the microwave LED may be resonant frequency that make you see the light dance more than other appliances.
« Last Edit: 21/09/2014 11:07:29 by peterloo »
 

Offline richardash1981

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Re: Why does my electric toothbrush make my oven misbehave?
« Reply #3 on: 21/09/2014 17:32:45 »
You might like to try two related experiments:
  • Use the toothbrush whilst looking at on old-fashioned CRT monitor - the picture should seem to break up like the LED digits do, for the same reasons (the CRT picture keeps being repainted with the picture 60-85 times a second, even if it isn't changing)
  • Try crunching a thick-cut potato crisp whilst looking at the same things - you should see the same effect from the vibration of the crisp breaking!
 

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Re: Why does my electric toothbrush make my oven misbehave?
« Reply #3 on: 21/09/2014 17:32:45 »

 

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