Question:
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) lines of B must run from the S pole to N pole.
Solution:
C is the amperian loop which is given as
$\int_{Q}^{P} \vec{H} \cdot \overrightarrow{d l}=\int_{Q}^{P} \frac{\vec{B}}{\mu_{0}} \cdot \overrightarrow{d l}$
Solving the above equation we get the angle between
$\vec{H}$ and $\overrightarrow{d l}$ more than $90^{\circ}$ so that $\cos \theta$ is negative.
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