How to measure resistance with a voltmeter

If great accuracy is not required when measuring resistance, then you can use a conventional analog voltmeter for this purpose. To do this, you need to know him internal resistance Rv, the value of which is usually indicated on the voltmeter.

To measure the resistance with a voltmeter, it is connected in series with the measured resistance Rx, which is short-circuited using the SB button.

Circuit for measuring resistance with one voltmeter

Circuit for measuring resistance with one voltmeter

When the button SB is pressed, the readings of the voltmeter are determined, that is, the mains voltage Uc is obtained, after which the button is opened and the readings of the voltmeter Uv are recorded.

You can determine the current in the network I = Uv / Rv. Then find the voltage drop across Rx equal to IRx = (Uv / Rv) Rx = Uc — Uv

Therefore, knowing the readings of the voltmeter when the button Uc is pressed and with Uv open and the internal resistance of the voltmeter Rv, you can determine the measured resistance Rx by the formula Rx = (Uc / Uv — 1) Rv.

How to measure resistance with a voltmeter

 

We advise you to read:

Why is electric current dangerous?