Question: Q. 4. From molecularviewpoint, discuss the temperature dependence of susceptibility for diamagnetism, paramagnetism and ferromagnetism.
U] [SQP II 2017]
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Solution:
Ans. Diamagnetism is due to orbital motion of electrons in an atom developing magnetic moments opposite to applied field as a result of which, resultant magnetic moment of diamagnetic material is zero. Hence, susceptibility of diamagnetic material is not much affected by temperature.
Paramagnetism and ferromagnetism are due to alignments of atomic magnetic moments in the direction of the applied field. As temperature is raised, this alignment is disturbed, resulting decrease in susceptibility of both, with increase in temperature. AT Q. 5. (i) How is an electromagnet different from a permanent magnet?
(ii) Write two properties of a material which make it suitable for making electromagnets.
R [O.D. Comptt. I, II, III 2014]
Ans. (i) An electromagnet consists of a core made of a ferromagnetic material placed inside a solenoid. It behaves like a strong magnet when the current flows through the solenoid and effectively loses its magnetism when the current is switched off. $1 / 2$
(a) A permanent magnet is also made up of a ferromagnetic material but it retains its magnetism at room temperature for a longer time after being magnetised once.
(ii) (a) High permeability
(b) Low retentivity
(c) Low coercivity (Any Two) $1 / 2+1 / 2$
[CBSE Marking Scheme 2014]
