Why is the speaker next to the camera magnetized when my laptop is off?

I'm on a mid 2010 15 inch mbp. I just noticed that, even after my computer has been off for a few days, coins are sticking to the back of the display - in the exact area of the speaker next to the built in camera (is that a speaker or a mike?)

I assumed that once my computer's been off for a long time, any type of magnetic fields will be long gone (and definitely not strong enough to move nearby coins!). Is it possible for this to occur, or should i look into some sort of problem (ie, the speaker/mike and/or camera staying on after my laptop has been powered off or put to sleep)

The microphone and speakers on Apple laptops are located in the lower case, not in the display. What you are noticing are the permanent magnets installed in the display to keep the lid closed without a mechanical latch.

Loudspeakers use permanent magnets, unaffected by electricity.

If you pass an alternating current through a coil of wire, it will induce a magnetic field in the coil. If you put 2 magnets in close proximity, opposite poles will attract, similar poles will repel. Conversely, if you move a coil of wire near to a magnet, it will generate electricity.

This is the basic principle of loudspeakers & microphones, massively over-simplified.

Full overkill explanation can be found on Wikipedia - http://en.wikipedia.org/wiki/Loudspeaker

Also, basic principles at http://en.wikipedia.org/wiki/Electromagnet