磁気

All magnets have two poles: north (N) and south (S). Like poles repel each other, while unlike poles attract. Both poles attract unmagnetized iron. This fundamental property applies to all magnets, regardless of size, making magnetic poles inseparable and always paired together.

When a magnet is broken into pieces, each piece retains both a north and south pole. Magnetic monopoles—isolated individual poles—are never observed in nature. This differs from electric charges, where positive and negative charges can exist independently. Every magnetic fragment, no matter how small, contains a complete north-south pair.

A compass needle is a thin bar magnet suspended at its center, allowing it to rotate freely in a horizontal plane. Earth acts like a giant magnet with its magnetic south pole near the geographic North Pole. The compass's north pole is attracted toward Earth's geographic North Pole because of this magnetic alignment.

Magnetic declination is the deviation between Earth's magnetic axis and its geographical axis. The Earth's magnetic south pole is located near the geographic North Pole, but these axes don't coincide perfectly. This angular difference affects compass navigation and must be accounted for in precise directional measurements.

In 1819, Danish physicist Hans Oersted observed during a lecture demonstration that a compass needle moved when current flowed through a nearby wire. This observation led to further investigation confirming that electric current could generate magnetic force. This discovery established the fundamental connection between electricity and magnetism.

When an unmagnetized iron nail is brought into contact with a bar magnet, it becomes magnetized. The magnetic field from the bar magnet aligns the atomic structure of the iron, causing the nail to acquire magnetic properties and behave like a magnet itself.

Magnetism enables numerous technologies including electric motors, generators for hydroelectric and renewable power, MRI medical imaging, computer hard drives, tape recording, and magnetic levitation trains. Recycling facilities use magnets to separate iron from waste. Ongoing research explores magnetic containment for fusion energy and brain activity mapping.