✤ Magnet -     It is a material that has both attractive and directive properties.

                         The property of attraction is called magnetism.

✤ Artificial Magnets

          The pieces of iron & other magnetic materials can be made to acquire the properties of natural magnets.

          Such magnets are called artificial magnets.

                 Eg> Bar magnet > bar of circular on rectangular cross-section.

                 House-shoe magnet > shape of a horseshoe & thus it has been named

✤ Properties of Magnets. (Poles)

      i) Same pole repels each other.

      ii) Opposite pole attracts each other.

      iii) We cannot separate the pole.

      iv) If magnet is cut in horizontal direction, then pole strength become half.

      v) If it is cut in perpendicular direction, then pole strength remain same.

      vi) Magnetic poles always exist in pairs.

✤ Some important definitions connected with magnets

      i) Magnetic field:-

           The space around a magnet within which its influence can be experienced is called its magnetic field.

      ii) Uniform Magnetic field:-

           A magnetic field in a region is said to be uniform if it has same magnitude and direction at all point of that region.

      iii) Magnetic poles

           These are the regions of apparently concentrated magnetic strength in a magnet where the magnetic attraction is max.

      iv) Magnetic axis

           The line passing through the poles of a magnet is called the magnetic axis of the magnet.

      v) Magnetic length

           The distance b/w 2 poles of magnet is called magnetic length of magnet, slightly less than the geometrical length of the magnet.

✤ Coulomb's Law of Magnetic Force:

          force b/w two poles

                        F=m₀/4pi. qm₁ qm₂/r²

✤ Magnetic Dipole

          An arrangement of 2 equal & opposite magnetic poles separated by a small distance is called a magnetic dipole..

✤ Magnetic Dipole Moment

         The magnetic dipole moment of a magnetic dipole is defined as the product of its pole strength & magnetic length

   Direction South pole to North pole.

                  m=qx2l (Am²/JT-1)

                  M=mx2l

        here m= Pole strength.

✤ Magnetic line of force

            May be defined as the curve the tangent to which at any point gives the direction of the magnetic field at that point. It may also be defined as the             path along which a unit north pole would trend to move it free to do so.

✤ Properties of lines of force

             Magnetic lines of force are closed curves. Never Cross each other.

            They start from & end on the surface of the magnet normally

            The lines of force have a tendency to contract lengthwise and expand sidewise.

      Magnetic Field of a Bar Magnet at an axial point

              or, l<<<<< n, I _neglet

                    Baxial =

      Torque on a Magnetic Dipole in a magnetic field.

                    τ = mBsinθ

                    τ = m x B          here M = m x 2d (dipole moment)

  Special Case :-        θ = 0°, sinθ = 0,

                     then τ = 0 (minimum)

                                  θ = 90°, sinθ = 1

                     then T = mB (max)

Current Loop as a magnetic Dipole

           m = IA (Am²) [AL²]

   For N turns

          M = NIA

          Unit is Am²

Gauss's Law in Magnetism

 States that the surface integral of a magnetic field over a closed surface is always zero:          ∮ B.ds = 0

              magnetic dipole produced by :-

              revolving e⁻:→ M = nhe/4πm,              h→planck's Constant,

                                                                          m= mass of e⁻,

                                                                          n.E Quantum Number

  Bohr magneton = he/4πm.

✤ Magnetic permeability: Magnetic permeability of a material is equal to the ratio of the magnitude of magnetic induction(B) to the magnetizing force (H).

                        μ = B/H unit is TmA⁻¹ or Wbm⁻¹ [MLT⁻²A⁻¹]

✤ Relative permeability: It is defined as the ratio of magnetic permeability of the material(μ) and magnetic permeability of free space (μ₀)

                         μᵣ= μ/μ₀

✤ Intensity of magnetization: It is defined as the magnetic moment per unit volume.

                    I = M/V I=m/a                     [M⁰L⁻¹A]

✤ Magnetic susceptibility: It is defined as the ratio of intensity of magnetisation (I) and magnetizing force(H)

                         χm = I/H

               Note : - χm= μᵣ-1

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