Ammeter Voltmeter Method

In this topic, you study the theory & diagram of the Ammeter-voltmeter method.

It is a very common, simple and quick method of measuring the low value resistances. As shown in Fig. 1 the connections are made and both the current and voltage drop across the resistance are simultaneously measured by the ammeter and voltmeters.

Fig. 1. Ammeter-voltmeter method.

The accuracy mainly depends upon the accuracy and range of the instruments employed for the measurement of current and voltage.

Here are current through the ammeter (I) is the sum of the current in voltmeter (I_V) and resistance (I_R), so

I = I_V + I_R

or,

I_R = I – I_V

$\text{True value of the resistance}~\text{ }$

\[\text{= }\frac{\text{Voltage across the resistance}}{\text{Current in the resistance}}\]

\[\text{= }\frac{\text{V}}{\text{I – }{{\text{I}}_{\text{V}}}}\text{  Ohm}\]