28.1
Magnetism
Magnets are commonly found in everyday objects, such as toys, hangers, elevators, doorbells, and computer devices. Experimentation on these magnets sh…
Magnetism was first observed over 2500 years ago near the ancient city of Magnesia.
Magnets can be found in everyday objects like speakers, credit cards, compasses, and memory devices.
A bar magnet has a North and South pole. When an unmagnetized iron nail is brought in contact with it, it becomes magnetized.
Like poles of a magnet repel each other, while unlike poles attract each other.
A magnet's poles cannot be separated by breaking them into two pieces. Instead, smaller magnets, each with a north and south end, are obtained. Hence, magnetic monopoles are never observed.
In a navigation compass, the needle is a thin bar magnet suspended at its center.
The north pole of a compass is attracted close to the Earth's geographic North Pole.
Earth also acts like a huge bar magnet, with its magnetic south pole near the geographic North Pole and its magnetic north pole near the geographic South pole.
The axis of the Earth’s magnet and the geographical axis do not coincide. This deviation is called magnetic declination.
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Q1: What are the two poles of a magnet and how do they interact?
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.
Q2: Why can't magnetic monopoles be isolated?
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.
Q3: How does a compass needle work?
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.
Q4: What is magnetic declination?
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.
Q5: How did scientists discover that electric current produces magnetism?
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.
Q6: What happens when an unmagnetized iron nail contacts a bar magnet?
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.
Q7: What are some modern applications of magnetism in technology?
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.