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Physics Theory : Magnetic Fields

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Magnetic field is the space around the magnet where its magnetic power or influence can be detected.
The magnetic field is filled with magnetic lines of force.


Magnetic line of force is defined as the closed continuous curve in a magnetic field along which the north pole will move if free to do so, and its direction is given by the direction in which the isolated north pole will point.
Magnetic lines of force have the following main characteristic features.
1. They are closed continuous curves.
2. They never intersect each other.
3. They mutually repel each other.
4. They contract laterally, i.e., they bend along the length of the magnet.
5. Outside the magnet, they travel from north to south.
6. Inside the magnet, they travel from south to north.
Magnetic lines of force can be drawn with the help of a plotting compass.


Magnetic induction is the phenomenon due to which an unmagnetized magnetic material behaves like a magnet by the mere presence of another magnet (referred to as the inducing magnet), which is not actually in physical contact with the magnet.
Thus, if a piece of soft iron is placed in the magnetic field of another magnet, then it would get magnetized by the process of magnetic induction.
During magnetic induction, the end of the unmagnetized magnetic substance that is nearer to the poles of the inducing magnet acquires opposite polarity, whereas the end that is farther acquires similar polarity.
The poles that are formed in the unmagnetized magnetic substance after magnetic induction are referred to as the induced poles.
The degree of induced magnetism depends on the nature of the magnetic material. It is directly proportional to the strength of the inducing magnet, and inversely proportional to the distance between the inducing magnet and the magnetic material.
Magnetic induction precedes magnetic attraction.


Domains are the millions of regions that magnetic substances have.
Each of these domains acts as a tiny magnet.


The Earth behaves like a huge magnet.
The area around the Earth where its influence can be detected is referred to as the Earth's magnetic field.
The shape of the Earth's magnetic field is similar to that of a giant bar magnet buried at the Earth's center along the geographic north and south poles of the Earth.
The south pole of this buried magnet is toward the geographic north pole of the Earth and the north pole of this magnet is toward the geographic south pole of the Earth.
The angle made between the magnetic north pole and the true geographic north pole of the Earth is called the angle of declination or variation.
The magnetic field of the Earth is strongest at the magnetic north and south poles.
It is weakest near the equator.
It has been found that the Earth steadily induces its own magnetic poles into a bar magnet kept in some place for a few weeks.
This results in the weakening of the magnetic force or power of the bar magnet.
To prevent this loss of magnetism, magnetic keepers are used.


Magnetic keepers are the pieces of soft iron that are placed across the poles of a bar magnet or a horse-shoe magnet.
They help prevent the loss of magnetism and preserve the magnetism by forming closed magnetic chains.


Physics Quiz on Magnetic Fields.
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