12th Class Physics Sample Paper Physics Sample Paper-3

  • question_answer Dictate different expressions obtained through Curie law in magnetism. Represent these expressions through graphs also. A saturation region is obtained in one of the graphs, why?

    Answer:

    Curie discovered experimentally that, the intensity of magnetisation (I) of a paramagnetic substance is directly proportional to external field \[{{B}_{0}}\]and inversely proportional to the absolute temperature (T) of the material. Mathematically,             \[I\propto {{B}_{0}}/T\Rightarrow I=C{{B}_{0}}/T\] where, C is known as Curie constant. Variation of intensity of magnetisation with \[{{\mathbf{B}}_{\mathbf{0}}}\mathbf{/T}\] We know that,    \[B={{\mu }_{0}}H\] \[\therefore \]      \[I=C{{\mu }_{0}}H/T\Rightarrow I=KH/T\] where,   \[K={{\mu }_{0}}C=\] another constant \[\therefore \]      \[\frac{1}{H}=\frac{K}{T}\Rightarrow \chi =\frac{K}{T}\]            \[\left[ \because \chi =\frac{1}{H} \right]\] i.e.        \[\chi \propto \frac{1}{T}\] In the variation of intensity of magnetisation with \[{{B}_{0}}/T\] a saturation region is obtained. At a particular stage, all the atomic dipoles present in the specimen align in the direction of the external field and this leads to saturation region.


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