Following are some of the basic properties of magnets.
A magnet attracts magnetic substances like iron steel cobalt nickel towards it when a magnet is put in a heap of iron fillings they cling to the magnet the attraction appears to be maximum at the two ends of the magnet these ends are called poles of the magnet.
When a magnet is suspended freely with the help of an unsung thread it comes to rest along the north south direction. If it si turned from this direction and left it again returns to this direction. The pole which points towards geographic note is called North Pole (N) and the pole which points towards geographic sound is called South Pole (S).
It should be clearly understood that poles exist always in pairs; two poles of a magnet are always of equal strength. Further poles N and S are situated a little inwards from the geometrical ends A and B of the magnet the magnetic length (NS) of magnet is roughly 6/7 of its geometric length (AB) we represent NS by 2/* (and not I).
The straight line XX' passing through north and south poles of a magnet is called axial line of the magnet in a direction perpendicular to the length of the magnet is called equatorial line of the magnet.
The straight line joining north and south poles of a freely suspended magnet represents magnetic N - S direction. A vertical plane passing through N - S line of a freely suspended magnet is called magnetic meridian.
Like poles repel each other and unfiled poles attract each other. To show this we suspend a bar magnet with another magnet near the N pole of suspended magnet we observe repulsion similarly south pole of one magnet repels south pole of the other however when S pole of one is brought near N pole of suspended magnet there is attraction
The force of attraction or repulsion F between two magnetic poles of strengths m1 and m2 separated by a distance r is directly proportional to the producers of pole strengths and inversely proportional to the square of the distance between their centers
F∝ m1 m2 / r2 or F = K m1 m2 / r2
Where K is magnetic force constant,
In S.I units K =\ μ0 / 4π = 10-7 Wb A-1 m-1
Where μ0 is absolute magnetic permeability or free space (aired/vacuum),
F = μ0 / 4π m1 m2 / r2
This is called coulombs' law of magnetic force* however in system the value of K = 1
SI unit f magnetic pole strength
Suppose m1 = m2 = m (say)
R = 1m and F = 10-7 N
From (1) 10-7 = 10-7 (m) (m) / I2
Or m2 = 1 or m = ± 1 ampere -metre (Am)
Therefore strength of a magnetic pole is said to be one ampere-metre, if it repels an equal and similar pole with a force of 10-7 N, when placed in vacuum (or air) at a distance of one metre from it.
The magnetic poles always exist in pairs magnetic monopoles do not exist. In an attempt to separate the magnetic poles, if we break a magnet we find new poles formed at the broken a magnet we find new poles formed at the broken ends. If the two pieces are broken again, we find the broken ends contain new poles again, thus each piece, however small are a complete magnet. Thus we cannot isolate the north or South Pole of a magnet. Unlike electric charge isolated magnetic north and south poles known as magnetic monopoles die not exist.
Inductive prosperity when a piece of magnetic material likes soft iron. Cobalt nickel etc. is placed near a bar magnet it acquires magnetism. The magnetism so acquired is called induced magnetism and this property of magnet is called inductive property.
Repulsion is the sure test of magnetism. Suppose we have two identical pieces one is iron and other is a magnet. To distinguish which is which we take another bar magnet. This bar magnet would attract the iron piece4 and also one end of this bar magnet would attract the opposite pole of the given magnet. However one end of this bar magnet would repel only like pole of the given magnet.
Hence when repulsion occurs between the testing bar magnet and one of the two given pieces, that piece must be a magnet. That is why we say that repulsion is sure test of magnetism.
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