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Effect of magnetism

  1. Jan 7, 2010 #1
    Can anyone explain to me why does a watch stop when it is brought near a magnet?I want to know how does the magnet affect the watch.
  2. jcsd
  3. Jan 8, 2010 #2
    The answer is depends on what "type" of watch. Digital/no moving parts? Mechanical?

    In a mechanical watch, you are influencing the interaction of the ferrous mechanical parts. Some could become magnetized, permenantly affecting the watch's performance.
  4. Jan 12, 2010 #3
    I have tried out with three types of watches.One of them is the spring-run watch of the olden days.Another one is the modern wrist watch, run on battery.And the 3rd one is also a modern wrist watch working on battery but the hands of the watch and the dial are made of plastic(none is digital).The magnet has no effect on the spring-run watch but it strongly effects the other two watches.So, we can see that a magnetic field affects the 2nd and 3rd watches.We know that the Earth has a magnetic field..So my question is that why Earth's magnetic field does not affect the parts of the watches, when it can affect a magnetic needle(since the parts of a watch are very small, I have compared their strength with that of a needle)?
  5. Jan 13, 2010 #4


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    I would be highly suspicious of a quartz watch being affected by a magnet. They do not have any mechanical motion outside of any physical hands and such. The timing mechanism, the quartz crystal, is fairly resistant to magnetic fields from what I know. A mechanical watch is affected because as previously stated the magnetization of the parts will create additional forces on the gears and such which will result in inaccurate running. A watch has to be very very precise to keep decent precision throughout the day, some mechanical watches easily run at around 20,000 beats per hour. That's 480,000 beats a day. If the watch gains say 4 seconds a day, then that means that each beat is only off on something of the order of a millionth of a beat. So even small imbalances can add up over time.

    However, fortunately, any decent mechanical watch will have magnetic shielding in the form of a thick iron plate that sits behind the watch mechanism (though this is not there for watches with skeleton backs so that you can observe the mechanism). This help keep the watch from being affected by a magnetic field. If a watch does become magnetized, I have heard that the affects are rather pronounced, something on the order of minutes for each hour. A watchmaker can demagnetize the watch and correct the problem.
  6. Jan 13, 2010 #5
    U are saying that the quartz watch should not be affected by a magnet.But then how does the magnet affect the watch?I have tested it several times.U can also test it.
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