With a bar magnet where are the lines of force closest together?

The lines of force near the magnetic poles are close together.

Explanation:

The magnetic lines of force originates from the north pole and ends at the south pole. The lines of force form the closed curve. They can never intersect each other.

The lines of force near the poles are close together. The lines of force near the magnetic poles have highest density. The magnetic force is strongest at the poles and it is weaker at the center.