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# Why is the direction of the magnetic field inside a bar magnet from S to N?

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As a convention, the field lines due to a permanent bar magnet have a direction at any point outside the magnet along the direction that a tiny magnetic compass needle shows. Since like magnetic poles repel and opposite poles attract, the compass north, $N_{com}$ always stays in a direction away from the bar north, $N_{bar}$ as long as the compass is outside the bar magnet.

However, if we drill a longitudinal tunnel through the bar magnet and insert our tiny compass, then $N_{com}$ will be towards $N_{bar}$.

Why?

Refer to this figure: