Of the following electrical methods which methods make use of the electric fields naturally present in the earth ?
(i) SP method
(ii) Resistivity methods
(iii) Equipotential line method
(iv) Induced polarisation method
(v) Telluric current method
(vi) Electromagnetic methods
MH SET - 2020, SET Exam - 2020,
Answer: B
The methods that use natural electric fields are (i) SP and (v) telluric current.
The self-potential method measures natural voltages produced by electrochemical reactions around ore bodies (especially sulphides), by streaming of groundwater and by other natural processes. The telluric method measures natural electric currents induced in the Earth by variations in the geomagnetic field.
Resistivity, equipotential-line and induced-polarisation methods all inject an artificial current into the ground, and electromagnetic methods use an artificial transmitter, so they are active, not natural-field, methods.
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