Toothbrush

[simonjp]

I have an electric toothbrush made by Philips. there are no physical connections between it and its recharge station. How does it get recharged?

[Sensei]

When you pass an electric current through a coil, a magnetic field is produced. Conversely, when you pass a magnetic field through a coil (or vice versa), there is an electric current produced in the coil. So, the base of the toothbrush is producing an oscillating magnetic field (you need movement to induce current in the coil) and the coil in the toothbrush is producing an electric current due to the changing field and storing that power in a rechargeable battery. That's the basic theory.

[GeorgeR]

I don't think it's quite like that. The questioner wants to know how the battery is recharged when not in use. When the brush is placed in its holder, it sits in an electric coil, which forms one half of a transformer. The other half is in the brush. A reduced voltage is induced in the battery of the brush, so recharging it. Simple, innit?

[simonjp]

Thanks guys... I've a feeling I might soon be needing a diagram! George, are you saying that Sensei is incorrect when (s)he says that there is an oscillating field? I'm a bit confused as to how the two theories are different. Thanks again, Simon.

[GeorgeR]

Well, I was really just being polite. The first answer is nothing to do with it. (In my humble opinion, of course!)

[Eddiecurrent]

Sensei is correct.A transformer can't operate unless it is subject to an alternating (oscillating) electric current, the voltage is not induced in the battery but in the coil in the toothbrush with is then rectified into DC and regulated so that the voltage isn't too high so that it cook the battery, in many respects your answers are virtually the same but with a little less technical depth. I would go for Sensei answer as it contains the greater technical understanding not shown in GeorgeR's incidentally it is not a pure transformer as there is no physical (such as an iron core) magnetic circuit by which all transformers operate.