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)

  • IIRC, what may look like a tiny speaker is just holes for the LED indicating camera activity. – Daniel Beck Sep 16 '14 at 13:35
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    @blueintegral Actually, many coins are magnetic. Please remember that your experience in one country is not necessarily typical of the whole world. Magnetic coins are common in the UK: 1p and 2p coins have been magnetic since 1992, and 5p and 10p coins since 2010 (source: the Royal Mint). 1, 2 and 5 Euro cent coins are also magnetic. That's already 390+ million people who have regular access to magnetic coins. – David Richerby Sep 16 '14 at 15:04
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    @blueintegral "I, like the majority of the world's population" No. You are not remotely like the majority of the world's population. Many European coins are magnetic; most Indian coins are made of steel so are presumably magnetic; some denominations of Chinese coins are made of steel so are presumably magnetic. I'm not denigrating: I'm pointing out that you're wrong. Do not assume that the whole world is like your home because it isn't. – David Richerby Sep 16 '14 at 23:33
  • The last three comments including this one wouldn't be here to waste our time if you had omitted your original condescend and just told us about the money. @DavidRicherby – Mazura Sep 17 '14 at 9:23
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    @Mazura it is not condescending to point out an actual false assumption. – JamesRyan Sep 17 '14 at 9:53

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.

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    This is the correct answer. Also—fun fact—magnets like those are sometimes used to tell the laptop when it's closed or not. I don't think that's the case with MBPs, but you can make some laptops sleep just by touching a magnet to them in the right place. Also, I think that the MBP has a mic by the camera as well for background noise reduction. If there's a hole, there's a mic. A speaker will rarely if ever only have one hole. – krs013 Sep 16 '14 at 9:49
  • images.anandtech.com/doci/4205/MBP2011-5600.jpg is a picture of what the front part of that section of the mbp looks like. do these magnets require vents? – blueberryfields Sep 16 '14 at 15:27
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    @blueberryfields: See my comment to the question, that's just where the camera activity indicator LED is. Open Photo Booth to activate the camera to see for yourself. – Daniel Beck Sep 16 '14 at 18:48

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

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    Also, I doubt that the electromagnet would have any difference between being silent and 'off'. – 0942v8653 Sep 15 '14 at 18:53
  • I added Wikipedia's electromagnet page to my answer, for completeness, as it covers many uses [I was initially thinking in terms of a 'true' electromagnet being DC only, but that, of course, is incorrect - my bad] – Tetsujin Sep 15 '14 at 18:59
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    While what you say it's true, the real answer is @paul's one. – o0'. Sep 16 '14 at 7:32
  • Indeed it may be - I was going from "in the exact area of the speaker next to the built in camera (is that a speaker or a mike?)" as I don't have an MBP, I was unaware of the magnetic lid – Tetsujin Sep 16 '14 at 7:46

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