Properties of Bar Magnet || Magnetism and Matter Class 12, JEE & NEET


Playing with magnets is one of the first moments of science most children discover. That’s because magnets are easy to use, safe, and fun. They’re also quite surprising. Remember when you first discovered that two magnets could snap together and stick like glue? Remember the force when you held two magnets close and felt them either attract (pull toward one another) or repel (push away)? Here we will study about the Bar Magnet and Properties of Bar Magnet!

A bar magnet is a rectangular piece of the object. It is made up of iron, steel or any other ferromagnetic substance or ferromagnetic composite, having permanent Magnetic Properties. The magnet has two poles: a north and a south pole. When you suspend it freely, the magnet aligns itself so that the north pole points towards the magnetic north pole of the earth.

Properties of Bar Magnet :

  1. Attractive Property and Poles : When a magnet is dipped into iron fillings it is found that the concentration of iron filings, i.e., attracting power of the magnet is maximum at two points near the ends and minimum at the center. The places in a magnet where its attracting power is maximum are called poles while the place of minimum attracting power is called the neutral region.

                                 

(2) Directive Property and N-S Poles : When magnet is suspended its length becomes parallel to N-S direction. The pole pointing north is called the north pole while the other pointing south is called the south pole.

(3) Magnetic Axis and Magnetic Meridian : The line joining the two poles of a magnet is called magnetic axis and the vertical plane passing through the axis of a freely suspended or pivoted magnet is called magnetic meridian.

                                   

(4) Magnetic Length  : The distance between two poles along the axis of a magnet is called its effective or magnetic length. As poles are not exactly at the ends, the effective length is lesser then the actual length of the magnet.

(5) Poles Exist in Paris : In a magnet the two poles are found to be equal in strength and opposite in nature. If a magnet is broken into number of pieces, each piece becomes a magnet with two equal and opposite poles. This shows that monopoles do not exist.

                                     

(6) Consequent-poles and No-pole : Monopoles do not exist in a magnet but there are two poles of equal strength and opposite nature :

                                         

(a) There can be magnets with no poles, e.g., a magnetised ring called toroid or solenoid of infinite length has properties of a magnet but no poles.

(b) There can be magnets with two similar poles (or with three poles), e.g., due to faulty magnetisation of a bar, temporarily identical poles at the two ends with an opposite pole of double strength at the centre of bar (called consequent pole) are developed.

(7) Repulsion is a Sure Test of Polarity : A pole of a magnet attracts the opposite pole while repels similar pole. A sure test of polarity is repulsion and not attraction, as attraction can take place between opposite poles or a pole and a piece of unmagnetised magnetic material due to ‘induction effect’.

(8) Magnetic Induction : A magnet attracts certain other substances through the phenomenon of magnetic induction i.e., by inducing opposite pole in a magnetic material on the side facing it as shown in fig.

                                     

(9) Magnetic and Non-magnetic Materials : The substances such as steel, iron, cobalt and nickel, etc., which are attracted by a magnet are called magnetic while substances such as copper, aluminium stainless steel, wood, glass and plastic, etc. which are not attracted by the magnet are usually called non-magnetic.

(10) Permanent and Temporary Magnets : If a magnet retains its attracing power for a long time it is said to be permanent, otherwise temporary. Permanent magnets are made of steel, Alnico, Alcomax or Ticonal while temporary of soft iron, mumetal or stalloy.

(11) Demagnetisation : A magnet gets demagnetised, i.e., loses its power of attraction if it is heated, hammered or ac is passed through a wire wound over it.

(12) Magnetic Keepers : A magnet tends to become weaker with age owing to self-demagnetisation due to poles at the ends which tends to neutralise each other. However, by using pieces of soft iron called keepers, the poles at the ends are neutralised and consequently the demagnetising effect disappears and the magnet can retain its magnetism for a longer period.

                                                   

 

 

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Comments
  • August 5, 2020 at 9:17 am

    excellent, this helped me in test