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( 8 months ago )

Magnets and entropy

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Vanshika Bhatt

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( 8 months ago )

A system in equilibrium corresponds to a free energy minimum which is a compromise between a minimum of the internal energy with a maximisation of the entropy. When you introduce, say, an unmagnetised ferromagnet to a magnetic field, alignment of the atomic magnetic moments with the external field reduces the internal energy. So if the field is strong enough (i.e. a great enough reduction in internal energy) then magnetisation can occur at the expense of a decrease in entropy.

Note, however, that the total entropy of the universe does not decrease since you need to use a heat engine (e.g. your arm) to move the ferromagnet through the magnetic field which will itself generate entropy.

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Charles Kyobe

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( 8 months ago )

While teaching thermodynamics our chemistry teacher (physics syllabus covers only first law) told us that a process is reversible if and only if no entropy is created.

Coming back to everyday life while playing with magnets we have observed that some substances stay magnetized for a very very long time (that is to say permanently) while others lose their magnetism at a moments notice. Now since magnetism is induced in some materials permanently I conclude that some change in entropy takes place. Now how exactly does magnetism produce a change in entropy on a micro and macro scale ?

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