12th Class Physics Magnetism

  • question_answer 47)
      What are the dimensions of the magnetic susceptibility? Consider an H-atom. Guess an expression for  upto a constant by constructing a quantity of dimensions of out of parameters of the atom : Here, is the electronic mass, is electronic velocity,  is Bohr radius. Estimate the number so obtained and compare with the value offor many solid materials.

    Answer:

                      Magnetic susceptibility As  and  have same units and dimensions, hence  has no dimensions. In this question,  is to be related with We know that dimensions of [From Biot Savart's law, or  Dimensions of Where  is for charge] As  is dimensionless, it should have no involvement of charge  in its dimensional formula. It will be so if  and  together should have the value , as e has the dimensions of charge. Let                               ...... where a, b, c are the powers of ,  and  such that relation  is satisfied. Dimensional equation ofis Equating the powers of and , we get 0 = 1 +  or  = -1 ; 0 = 1 + b + c    ??            0 = -b or b = 0 ; From, 0 = 1 + 0 + c or c = -1 Putting values in, we get Here,


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