Question

So I am working on a lab for my Physics II class, where we are working with circuits. The title of the section I am working on is called "Internal Resistance of an Analog Voltmeter", just for reference.

We found the resistance of the analog voltmeter to be 5.02 K ohm. (We measured the resistance using a digital multimeter)

The voltage that was present in the circuit was 3.512 V, and the current was measured at 0.001 A.

When we calculated the resistance of the analog voltmeter using Ohm's Law, the value came out to be 3512 Ohm, which is far from the 5020 Ohm that was originally measured with the digital multimeter. I was wondering if this sounds right or not and why?

After browsing the internet for a bit, I found some stuff about the internal resistances of analog voltmeters being higher than that of their digital counterpart, but I don't know why. Please help! Thanks!

Answer 1

The most probable reason is error. Error can arise either due to lack of accuracy in taking measurements or due to bad precision of measuring instruments.

Mentioned current is 0.001 A or 1 mA a small error in measuring current have huge difference in calculation of internal resistance.

Next important thing is to verify the circuit. Is the voltage mentioned across said voltmeter only nothing in between. Is current mentioned is current through branch containing said voltmeter only or is it total current?

A circuit diagram would give better idea.

Further discussion welcomed, comment please.