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Assuming that there is three line of circuit and our amper ring is surrounded just two circuit . According to amper law the magnitude of B is just related to the circuits in the ring . But here the magnitude of B is affected by the circuit outside of the ring,too though it's not shown on the other side. Does it a paradox ?

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    $\begingroup$ Hi! It's not clear at all what you're talking about. For instance, what is a "line of circuit" ?? $\endgroup$ – Daddy Kropotkin Jun 11 '19 at 15:46
  • $\begingroup$ What's an amper ring? Is "amper law" supposed to be Ampère's law? $\endgroup$ – PM 2Ring Jun 11 '19 at 16:08
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I believe your confusion lies in when Ampère's law can be applied.

Ampère's law only applies in situations with sufficient symmetry, that is situations in which the magnetic field is the same at every point in the Ampèrian loop. For example in the case of an infinitely long wire.

I assume what you are talking about is a case with three parallel wires an you place an Ampèrian loop around two of them. In this case the magnetic field is evidently not the same around the entire loop. In this case you can use the Biot-Savart law which does not have any symmetry requirements.

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  • $\begingroup$ So we need to know about how the magnetic field is applied in problems . Thanks , now I understand it . Sorry for dictation :D $\endgroup$ – Alireza Oe Jun 12 '19 at 7:42

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