A magnet is an object that applies a force over a distance on other magnets or magnetic materials. This magnetic effect produced by a magnet is known as magnetism.
More than 2000 years ago lodestone ( a type of rock containing magnetic properties) was discovered.
- A magnet can attract magnetic materials
- A magnet has two poles
- Like poles repel and unlike poles attract
- A freely suspended magnet always points in a north-south direction.
A magnetic material is one which can be magnetized and is attracted to magnets.
All strongly magnetic materials contain iron, nickel, steel or cobalt.Aluminium, copper, gold and silver are nonmagnetic materials.Magnetic materials can be classified into further
- Ferromagnetic: few materials show a very strong attraction toward the pole of a permanent magnet. They are called ferromagnetic. materials of this kind are called ferromagnetic.For example iron. They are further divided into hard and soft materials.Hard magnetic materials are really hard to get magnetized. But, If they gets magnetized, it will be permanent.It is also called permanent magnetic material.such as steel, Alcomax and Magnadur. They are used i motors, mic, speaker, electronic and instrumentation. Soft magnetic materials are easy to get magnetized and demagnetizes.It is also called temporary magnetic material. Such as iron and Mumetal are relatively easy to magnetize.They are used in the cores of electromagnets and transformers.
Theory of Magnetism
Magnetic field created by the magnet is due to the motion of its electrons,which orbit the nucleus of each atom. Each atom represents a little magnet. The circulating electron produces magnetic effect. In magnetized material, magnetic fields of individual atoms are randomly aligned. When the material is magnetized, the magnetic fields of individual atoms come in same direction. Together, billions of small magnets act as a big magnet.
Magnets are dipole having a north and south magnetic pole. Opposite poles (N and S) attract, and like poles (N and N, or S and S) repel each other.
It is a region around a magnet in which a magnetic material experience a force of attraction or repulsion.
Force exerted by a magnet gets weaker if it is farther away from the magnetic field. If a magnetic material is placed outside the magnetic field, there will be no force exerted on it and the magnetic material will not be attracted or repelled by the magnet.
Magnetic Lines / Magnetic flux
A magnetic field is invisible. It can be visualized by imaginary magnetic lines of force around the magnet. These lines give the direction and strength of the field.We can draw Magnetic field pattern (lines of force) of a magnet by sprinkling iron filings around it or plotting it with the help of compass.
Properties of Magnetic lines
- Field lines run from the north pole to the south pole.
- Magnetic field is strongest, when the lines are closest.
- Magnetic lines between opposite poles is almost uniform.
- Magnetic lines between same poles repel each other and create neutral point.
Magnetic induction is a process in which magnetic material becomes a magnet, when it comes in contact or near to a magnet.
When a paper clip is brought near to a permanent magnet,it will be attracted to the
magnet due to magnetic induction.We can say,paper clip has become an induced magnet. In turn, Now,this induced magnet is able to attract other paper clips. The process does not require any physical contact. The N pole of the permanent magnet induces South pole in the nearer end of paper clip and an North pole in its farther end.
The Earth is a huge magnet with its north and south poles.We will call the pole which points towards the geographical north pole, the north pole of the magnet, and we will call the pole that points towards
the south, the south pole of the magnet. The earth’s magnetism is called geomagnetism.
Making a magnet
- Stroking Method: In this method, an unmagnetized steel bar being stroke several times by a permanent magnet in one direction.only one pole is used (S or N).After several strokes, Steel bar will be magnetized by magnetic induction.
- Electrical method / Electromagnetism: A steel bar or iron can be magnetized by placing it in a coil of wire and Passing a d.c through the wire will magnetize the bar.
Uses of Magnet
- Magnet door catcher
- Moving coil loud speaker
- Electronics and instrumentation
- Industrial lifting