The property of a magnet that determines which side is North or South is its polarity. Magnets have two poles, a North pole and a South pole, which are determined by the direction of the magnetic field lines.
The North pole of a magnet is usually marked with a letter N or a plus (+) sign, while the South pole is marked with a letter S or a minus (-) sign. You can also use a compass to identify the poles - the needle of a compass will always point towards the North pole of a magnet.
No, a magnet can only have one North pole and one South pole. The magnetic field lines of a magnet always flow from the North pole to the South pole, and cannot cross or merge.
No, the strength of a magnet does not affect which side is North or South. The polarity of a magnet is determined by its structure and the direction of its magnetic field lines, not by its strength.
Yes, the polarity of a magnet can be changed by exposing it to a strong magnetic field in the opposite direction. This process is known as magnetization, and it can be done using specialized equipment or by rubbing a magnet against a piece of metal in a specific way.