Define magnetic susceptibility of a material. Name two elements one having positive susceptibility and other having negative susceptibility.

Explanation

(1) Susceptibility : When a material is placed in a magnetic field, the ratio of the intensity of magnetization acquired by it to the intensity of the applied magnetic field is called its susceptibility.
Suspectibility `chi = ("Intensity of magnetisation , I")/("Applied magnetic field, H")`
(2) The susceptibility of a material represents its ability to get magnetism.
(3) Susceptibility is a dimension less quantity.
(4) Relation between `mu_(r)` and `chi` :
(a) Suppose that material is placed in a magnetic field of intensity H. Ley I be the intensity of magnetisation acquired by it.
(b) Then the magnetic induction with in the material is
`B = mu_(0) H + mu_(0)I rArr (B)/(H) = mu_(0)[1+(I)/(H)]`
`rArr mu = mu_(0)[1+ chi] rArr (mu)/(mu_(0)) = 1+chi`
`:. mu_(r) = 1+ chi [because mu_(r) = (mu)/(mu_(0))]`
(5) Negative susceptibility `(chi)` of diamagnetic elements are Bismuth `(-1.66 xx 10^(-5))` and copper `(-9.8 xx 10^(-6))`.
(6) Positive susceptibility of Ferromagnetic elements are Aluminium `(2.3 xx 10^(-5))` and oxygen at STP `(2.1 xx 10^(-6))`.
(7) Large and positive susceptibility of ferromagnetic elements are Cobalt and Nickel.