If a bar magnet is hung from a string, in which direction does its north pole point?

Correct — A. A bar magnet hung freely from a string turns until it lines up with the Earth's magnetic field, and it settles with its north pole pointing towards geographic north.

The pole is named for exactly that behaviour — it is the north-seeking pole. It is the property a magnetic compass is built on.

The Earth itself behaves like a huge bar magnet whose magnetic south lies near the geographic north, so unlike poles attract and the magnet comes to rest along the north-south line, as option (a) says.

Why the others are wrong

• (b)
  South — South is where the south pole of the same magnet comes to rest. Both ends settle at once along one line, and the question asks about the north pole, which swings to the opposite end of it.
• (c)
  East — East-west is not a rest position. A magnet left across the field lines feels a turning couple and rotates out of that position; only the north-south alignment is stable.
• (d)
  West — The same objection as east. Nothing holds the magnet on the east-west line, so it swings back until its north pole faces north again.

A magnet free to rotate feels a couple from the Earth's magnetic field: the field pushes its north pole one way and its south pole the other. The magnet stops turning only when the two forces lie along the same line.

That line runs roughly north-south, which is why a suspended bar magnet is a crude compass.

The apparent contradiction — a north pole attracted to the north — dissolves on the convention that the Earth's magnetic south pole sits near the geographic north pole.

Key facts

• A freely suspended bar magnet comes to rest along the north-south direction, with its north pole towards geographic north.
• The magnet's north pole is the north-seeking pole, which is what makes a compass needle work.
• The Earth's magnetic south pole lies near its geographic north pole, so unlike poles attract.
• The angle between magnetic north and geographic north at a place is called the magnetic declination.

Common traps

• Reasoning that the magnet's north pole is attracted to the Earth's north magnetic pole, which reverses the answer.
• Treating magnetic north and geographic north as the same direction.

No directly related past PYQ was found.