# Use (i) the Ampere’s law for H and (ii) continuity of lines of B,

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.