Loss of Charge Method to Measure Resistance and to Calculate the Resistivity of a Specimen

Loss of Charge Method to Measure Resistance and to Calculate the Resistivity of a Specimen

• Refer Figure in this figure when B is taken on position 1, the voltage is applied and circuit is charged. But after this if the switch B is taken to position 2, it is disconnected from the supply and the capacitance of the specimen is discharged through its own volume resistance. Discharging currents are taken in finite time intervals and we can obtain current time characteristic.
• The slope of this curve gives time constant

Time constant = CR where 

C = is the capacitance of the specimen.

Volume resistance R can be calculated time 

R = time (t) / C log_e V_a / V

Where t = time in seconds when voltage from normal voltage V_n to some voltage V and C is the capacitance in farad. 

From this, volume resistivity can be calculated 

ρ = π r² / Thickness (t) Ω cm