There are some substance on the earth which attract magnetic materials called magnets.
Magnets are of two types-
1. Natural Magnet:-
The material in which magnetic properties are inbuilt by origin is called Natural magnets.
2. Artificial Magnet:-
Some magnetic materials when placed in contact with natural magnets they start showing magnetic properties are called Artificial Magnet. Example- Hematite, magnetite,
Artificial magnets are of two types-
1. Permanent magnets-
If magnetic properties stay even after removal of the magnetic field then that material will be called a permanent magnet. Example- Steel, tungsten, alloys.
2. Temporary magnets-
if magnetism of the substance finish after the removal of the magnetic field then those substances are called temporary magnets. They are used in a generator, Motors, electric bells, etc.
Bar Magnet –
This is the simplest form of a magnet that is used in laboratories. It has two poles, north pole and South pole. When the bar magnet is handover the iron fillings there are two points on the magnet at which filling attracted very much. Those points are called magnetic poles.
Basic Properties Of Bar Magnet-
Every magnet attracts small pieces of magnetic substances like iron, nickel, Cobalt. The attraction is maximum at the ends of the magnets. When a magnet is suspended freely with the help of thread. It comes to rest along in a north-south direction this is called directive property of magnet.
Magnetic poles always exist in pairs. These poles can never be separated that is magnetic monopole cannot exist. If a magnet is cut into two parts. There will be a North and South wall existing on every part. Like Poles repels each other while opposite force attracts each other.
If a magnetic material is placed nearby the bar magnet is rubbed against that material then the magnetic material start showing magnetic properties and this property are known as inductive property of the material. A bar magnet can be demagnetized by heating, hammering, trucking and burying the bar magnet in the earth.
A magnet can attract another magnet. It can also attract magnetic material like iron, nickel, cobalt, etc. So repulsion is the real test of a magnet. Some substance is repaired by bar magnet which are called diamagnetic substances like water, gold, silver etc.
Some Important Definitions Related To A Bar Magnet-
- Magnetic pole and Pole strength- The points nearby the ends of a bar magnet at which magnetic strength is minimum those points are called magnetic poles. The strength to attract the magnetic materials by magnetic poles is called magnetic strength. It is represented by m and its unit is Ampere metre.
- Magnetic axis- The imaginary lines passing through the magnetic poles of a magnet is called magnetic axis.
- Magnetic meridian- The imaginary vertical plane passing through the bar magnet is called magnetic meridian.
- Effective length of a magnet- The length between magnetic poles of a bar magnet is called effective length of magnet. It is 5/6 of geometrical length.
Coulomb’s Law For Magnetic Pole –
According to this law if two magnetic poles are placed at a certain distance then the magnetic force acting between the poles will be directly proportional to the product of pole strength and inversely proportional to the square of the distance between the poles.
If two equal police strength are at a distance of 1 metre and the force acting between them is is in Newton then the magnetic poles are called unit magnetic pole.
The field around a magnetic pole in which another magnetic pole experiences a magnetic force is called a magnetic field.
Magnetic Dipole –
for a bar magnet if two equal but opposite magnetic poles are placed at a small distance then it is called magnetic dipole. For current carrying coil solenoid for current carrying loop there are two poles existing according to the direction of magnetic field.
Magnetic dipole moment-
For a bar magnet, a magnetic dipole moment can be defined as a product of all is strength and distance between the poles.
- Magnetic dipole moment equals to pole strength x distance between the poles.
- Direction of dipole moment is from South to North.