magnetic field lines are from north to south outside but inside it is from south to north why is that?

Answer 1

Think of the field as moving in a circle. We have defined north and south as those particular points. No other reason.

Answer 2

Unlike electric field, magnetic fields are CLOSED one.

Therefore, if we start from any point in the field, then the field must return to that point or must end with that point.

Hence a field starting from north pole of a magnet goes around the magnet and passes through the south pole of the magnet and again ends in the North Pole.

If we start from the south pole of the magnet, now the field direction is pointed toward the north pole of the magnet [Note it cannot oppose the fields that are coming from the north pole of the magnet], it passes through the north pole of the magnet and again reaches the south pole via out side of the magnet.

If you imagine that the fields are from north to south inside the magnet, then there will be two circles of fields one circle of field moving in clockwise direction and another moving in anticlockwise direction and hence they will nullify each other and there will be no field at all out side and inside the magnet.

Another way of explanation is as follows.

The field is the path along which a free unit north pole will move.

A unit pole placed at the point of North Pole of the magnet goes around the magnet and reaches the South Pole.

If the field inside the magnet were from North to south inside, then a pole placed at the north pole of the magnet will not move from the magnet, because now there are two field one pushing it out side and another pulling it inside.

Similarly a unit south pole placed at the south pole of the magnet will not move from that point because of two equal but opposite fields.

Answer 3

Magnetic Field lines usually extends from one End to the Other end... thats why if we cut a magnet, we still get both N and S ... from your Question.... In reality, the Earth Axis is not Fully Straighten!!! the Earth actually Tilts and their Field Lines are measured differently depending on the sun... But In Reality!!!! the Field Lines of the Earth starts from the South... and Protrude to the NORTH!!! but... due to our ignorance in the past, most maps gave name to the continent as North and South, but in reality.... they are actually the inverse!! it's a language thing.. not a physic concept

(opps, i thought u was referring to the Earth.. but i just keep this Answer for fun =)