Question

why magnetic lines starts from north pole?​

Answer 1

When a small north magnetic pole is placed in the magnetic field it will experience a force. These lines around the magnet represent the path of an imaginary independent north pole if it were allowed to move freely in the direction of the magnetic force.

Answer 2

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=> It is only a convention by which we decided to use a direction for these lines, just to ensure that everybody is using the same directions. The actual direction may be different. For example, we knew about the north and south poles of Earth and we named the end of magnet which was attracted to the north pole of Earth as the north pole. South pole of the magnet was similarly named. However, it was later found that Earth's north pole is close to its magnetic south pole (and that is why magnet's north pole is attracted to it).