CSIR-NET
2014
107.
Electrical measurements are made over a homogeneous medium passing
current through widely separated current electrodes and placing the
potential electrodes at distance of 10 m and 20 m from one of the
current electrodes. If the resistance measured is 2 ohm m, the
resistivity of the medium is..
a)
20 pi ohm m
b)
40 pi ohm m
c)
60 pi ohm m
d)
80 pi ohm m
Solution:
Pole-dipole
(Three point array) : In this configuration one of the current electrode is fixed at a great distance from the other three, all of
which can have varying spacing.
r1=10m=a
r3=20m=b
apparent
resistivity (ρa) = ((2*π*a*b) / (b-a) )* (ΔV /I)
---------------(1)
Resistance
(R) = ΔV / I
ρa
= {[(2*π*10*20) / (20-10) ]* (2)}
apparent
resistivity (ρa)=80 Π Ώm
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