# Electric Toothbrushes

1. Jan 6, 2004

### jimmy p

How do electric toothbrushes charge? The ones i have seen are all plastic casings and the chargers are made of plastic, or at least the casing is. Obviously plastic is an insulator, so how does the charge pass through a plastic coating, and then through another?

Thanx

2. Jan 6, 2004

### chroot

Staff Emeritus
Magnetic induction. Energy is carried through an oscillating magnetic field.

- Warren

3. Jan 6, 2004

### mmwave

Why? I haven't had one since I was 7 (I won't say how long ago that was but it was a long time). It had two little metal prongs that made contact with sockets in the brush for charging. Why would they seal it up and use the less efficient magnetic induction?

4. Jan 7, 2004

### chroot

Staff Emeritus
It's not that much less efficient, and it's safer.

- Warren

5. Jan 7, 2004

### HallsofIvy

The point is that one tends to use a toothbrush in a wet environment, often with wet hands.

6. Jan 8, 2004

### jimmy p

...ok then, so the charger has a powerful electromagnet inside it? does the toothbrush have a battery pack or a capacitor inside it?

7. Jan 8, 2004

battery pack

8. Jan 8, 2004

### chroot

Staff Emeritus
Just think about a transformer, with one set of windings on one side of the plastic, and one set of windings on the other.

- Warren

9. Jan 9, 2004

### mmwave

Ok, but transformers are generally wound sharing the same core and in this case it's not possible, hence less efficient than a normal transformer.

10. Jan 9, 2004

### jimmy p

ok cool, that sounds cool. Im suprised that is efficient though, to produce a strong enough magnetic field to induce a charge.

11. Jan 9, 2004

### mighty2000

It actually induces current and EMF. Look up Faradays law of induction.

It doesn't matter if there is a conductor in the way of the electromagnet or air, EMF will still be produced (mathematical path). However, in this case, there is a conductor with N turns in the path of the magnetic field, which will carry induced current and induced EMF. This induced EMF charges the battery inside the plastic.

M2k

Last edited: Jan 9, 2004