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Question:

(a) An iron ring of relative permeability μr has windings of insulated copper wire of n turns per metre. When the current in the windings is I, find the expression for the magnetic field in the ring. (b) The susceptibility of a magnetic material is 0.9853. Identify the type of magnetic material. Draw the modification of the field pattern on keeping a piece of this material in a uniform magnetic field.

Solution:

(a) :Copper wire windings on the iron ring forms a toroid.Magnetic field due to a toroid is given by B=μnI where μ is the permeability of the medium, n is the number of turns per unit length and I is the current flowing.Also, μ=μrμo ⇒ B=μrμo nI
(b) : Susceptibility of the magnetic material is given as χ=0.9853Since the magnetic susceptibility of paramagnetic material is positive. So the given substance must be a paramagnetic material.