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(Forgive my crude MS paint drawing) Magnetic field with small disturbance

Imagine we have a large magnetic field coming from a powerful source. At the edge of the field where it is weak (A), we introduce a disturbance using another magnetic field. However, at the edge the disturbance is a weak magnetic field that does not reach far in space.

Would the effect on the large field be detectible near the source? (at B or C)

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  • $\begingroup$ Sure, but it depends on the sensitivity of your apparatus. $\endgroup$ – user8718165 Oct 11 '19 at 18:18
  • $\begingroup$ Given that our detector is not sensitive enough to sense the small field A without the presence of the large field. $\endgroup$ – nickhansenrf Oct 11 '19 at 19:06
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There is no shield to stop the field of A from extending to B and C (and on to infinity). The field just gets weaker and weaker. It never becomes zero.

Whether it can be detected depends on how sensitive the detector is.

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  • $\begingroup$ That's fair but my question is if the effect on the larger field would be detectable, not the field from A by itself. Given that the field from A is weak so that it can not be detected at B or C by our imaginary detector, is it possible that the disturbance to the larger field could still be detected? $\endgroup$ – nickhansenrf Oct 11 '19 at 18:40
  • $\begingroup$ No, since the fields simply add. $\endgroup$ – G. Smith Oct 11 '19 at 20:35
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A field sensor setup along some direction detects the projection of the resultant (vector sum) intensity from all sources. If the sources are time independent then except for their individual directionality there is no way to separate them by the sensor but if one source is, say, periodically fluctuating then a proper filter tuned to the rate of fluctuation may be able to extract that part. A more complicated time function than a simple periodic sinusoidal one can also be separated and detected by a so-called matched filter, see any standard book on detection, especially radar. The ability of discriminating one source from another will depend on the particular filter and the operating signal to noise ratio after the filter.

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