The magnitude of the magnetic field on the axis of a circular current loop
is given by Eq. 2.If a coil carrying current magnetic field is measured as a function of
distance, this process is called magnetic mapping.Search coil is a small area coil of closely spaced number of turns, N and
area, A. If such coil is inserted in a space of varying magnetic field, an induced
emf is produced.is parallel to A, and A is constant, faraday's equation becomes; emf = -N.A dt dB If the rate of change of B is known, the magnetic field, B, can be measured
by measuring the induced emf.The field has its largest value in the plane of the loop and decreases as the distance z increases.where ?=???

The magnitude of the magnetic field on the axis of a circular current loop

is given by Eq. 2. The field has its largest value in the plane of the loop and decreases as the distance z increases. The direction of the field is determined by the

right-hand rule: grasp the wire in the right hand, with the magnetic field.
Search coil is a small area coil of closely spaced number of turns, N and

area, A. If such coil is inserted in a space of varying magnetic field, an induced

emf is produced. According to faraday’s law of induction, this emf depends on

the number of turns, area of the search coil and on the rate of change of the

magnetic field
emf = -N
dt
d
where  =
If  is parallel to A, and A is constant, faraday’s equation becomes;
emf = -N.A
dt
dB
If the rate of change of B is known, the magnetic field, B, can be measured

by measuring the induced emf. This procedure is known as calibration.
For a loop carrying current wire, the variation of B, if an alternating current,

of frequency f, is passed through is given by

dt
dB B f
t t
B B
.
2 1
2 1

−
−
t2 – t1=T/2=1/2f, where T is periodic time of the current source.
emf = -N.A
dt
dB
= −.fB=CB
where C= N.A.f is sensitivity of the given search coil.

If a coil carrying current magnetic field is measured as a function of

distance, this process is called magnetic mapping.