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Show the magnetic dipole moment in terms of pole strength. |
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Answer» Solution :The strength of magnetic pole is called pole strength. Magnetic dipole MOMENT per unit length of magnet is called pole strength of magnet. Charge `q` is like that in equations of static electricity, likewise pole strength is in magnetism. Pole strength is denoted by `q_(m)` or `P`. Pole strength depend on the type of material of magnet, its MAGNETIZATION position and area of cross section (A) of magnet. It is a scalar quantity. The unit of pole strength is ampere meter (Am). If the length of bar magnet is `(2l)` and pole strength `q_m` then magnetic dipole moment, `overset(to)(m) = q_m ( overset(to) (2l) ) ` The direction of ` overset(to)(m)` is from S to N. From this equation unit of m is `Am^(2)`. (Note : The magnetic force ACTING on a pole of a bar magnet kept in magnetic FIELD of 1 T is known is pole strength). `therefore q_m = (overset(to) (F_m) )/( overset(to)(B) ) therefore q_m = F_m [ because B = 1T] and overset(to) (F_m) = (q_m) (overset(to) (B) )` (This equation is similar to static electricity as per `overset(to) (F ) = q (overset(to)(E) )` ). As electric field by a point charge is`E= (kq)/( r^2)`, similarly magnetic field by a pole of pole strength `q_m` is `B = (mu_0)/( 4pi) (q_m)/( r^2)`. |
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