# Uncertainty in voltage

1. Aug 9, 2014

### Crovati

How does taking the voltage of a circuit before and after an experiment help with uncertainty in the voltmeter?
Our teacher instructed us to do this, and i got that voltage before was 1.516 and voltage after was 1.498.
Does this mean the voltmeter became less resistant? How do I turn this into an uncertainty?

2. Aug 9, 2014

### phinds

That is NOT a good way to figure out the uncertainty in a voltmeter.

There is no answer to the question as you have posed it. For example, a particular circuit might well have resistors that change values slightly as they warm up and so the voltage in a particular part of that circuit could have different values when the circuit is cold than when it has been warmed up. This would have nothing to do with any measurement uncertainty in the voltmeter, although it would change what you see as that uncertainty since you wouldn't know whether difference is measurements were due to the voltmeter or the changes in resistance values.