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(a) A circular coil of N turns has radius R and negligible cross section. A curr

ID: 2265157 • Letter: #

Question

(a) A circular coil of N turns has radius R and negligible cross section. A current I passes through

it. Calculate the magnetic ?eld at a point on the axis of the coil a distance z away from the centre of

the coil.

(b) Now consider two identical such coils, placed along a common axis and separated by a distance

equal to their radius. Evaluate the magnetic ?eld as a function of position z along the axis, and show

that on the axis midway between the coils the ?rst three derivatives of the magnetic ?eld with respect

to z vanish. What is the practical relevance of this system?

Explanation / Answer

a)u*i/(N*r^2)


b) they are in series as the field of first one passes through the second one