Last year, we challenged you to ask Planet Science a question.
Year 6 at the Willows Primary School in Staffordshire rose to the
challenge. They asked us "How does the electricity travel through
the plastic coating of an electric tooth brush and the plastic
coating of a charger, to re-charge my electric toothbrush. Surely,
there need to be metal contacts? There aren't and it charges?
That's a great question. We set off to investigate.
What's in your bathroom? Lots of water! So you don't want any
exposed metal on your charger. Water connecting with the metal
could stop the charger working and it could be dangerous.
How do electric toothbrushes charge if there are no
This sort of charging is called induction.
An electrical current produces a magnetic field. You can tell
there is a magnetic field near the wire because it moves a compass
needle. Turning the current on and off makes the magnetic field
near the wire appear and disappear. Have a look at this video:
Did you see in the last circuit that the battery was turned
round? This caused the current to flow in the opposite direction.
Current flowing in the opposite direction changes the direction of
the magnetic field. Did you see the compass needle swing round in
the opposite direction?
The current in the electricity supply to your house flips first
one way and then the other - it is alternating current
(AC). The current alternates - changes direction - around
50 times per second. This means that the small magnetic field
around the wires changes direction too.
Your electric toothbrush and charger both have a coil of wire
Diagram adapted from http://www.explainthatstuff.com/inductionchargers.html
The coil of wire inside the charger is powered from a plug
socket and creates a magnetic field, just like the wires in the
video. The magnetic field keeps changing direction as the current
How does the magnetic field produced by the charger coil
charge the battery in the toothbrush?
A moving magnetic field creates a current in a wire. The
changing magnetic field from the coil of wire in the charger
generates a current in the coil of wire in the toothbrush. The
electric current from the coil of wire in the electric toothbrush
charges the battery.