Among the following, which method is NOT preferred to measure low resistances?

The resistances are classified depending upon the values as:

• The resistances of the order of 1 Ω (or) less than 1 Ω are classified as low resistances.
• The resistances from 1 Ω to 100 KΩ are classified as medium resistances.
• The resistances of the order of 100 KΩ (or) higher are classified as high resistances.

The methods used for the measurement of low resistances are:

Ammeter Voltmeter Method:

Connecting voltmeter across the load is suitable for low resistance measurements.

Ammeter reading is:

\(I+I_V=\frac{E(R+R_V)}{R.R_V}\)

Voltmeter reading = E

The calculated resistance is:

\(\frac{E}{I+I_V}=\frac{R.R_V}{R+R_V}\)

Kelvin's Double Bridge Method: Kelvin's Double Bridge Method is a modification of the Wheatsone bridge method. 

The circuit diagram is shown below:

R is the unknown resistance and S is the standard resistance.

Potentiometer Method:

• It works by comparing the unknown resistance with the standard resistance.
• The voltage drop across the known and unknown resistance is measured and by comparison the value of known resistance is determined.

Note:

• Mega ohm bridge is used for measurement of high resistance.
• DC bridges are used to measure resistance.
• AC bridges are used to inductance and capacitance.