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Use i the Ampere's law for H and ii continuity of lines of B, to conclude that inside a bar magnet, (a) lines of H run from the N-pole to S-pole while (b) lies of B must run from the S-pole to N -pole. |
Answer» Solution :Consider amagnetic FIELD line of B through the bar magnet as given in the figure below.  The magnetic field line of B through the bar magnet must be a CLOSED loop. Let C be the amperian loop, then, `int_(Q)^(P)H. di=int_(Q)^(P)(B)/(m_(Q))di` We know that the ANGLE b etween B and Di is less than `90^(@)` inside the bar magnet so , it is positive. i.e., `int_(Q)^(P)H.di=int_(Q)^(R)(B)/(mu_(0))digt0` Hence, the lines of B must run from south POLE (s) to north pole (N) inside the bar magnet. According to Ampere's law, `therefore ointHdi=0` `therefore ointH.di=int_(P)^(Q)H.di+int_(Q)^(P)H.di=0` As `int_(Q)^(P)Hdlgt0,` So `int_(P)^(Q)H.dilt0` It will be so if angle between H and di is more than `90^(@)`, so that `cos theta` negative it means the line of H must run from N-pole inside the b ar magnet. |
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