# Input resistance (Input impedance)

1. Sep 14, 2010

### wavingerwin

1. The problem statement, all variables and given/known data
A digital voltmeter is used to measure the resistance and voltage of a circuit.
The resistance and voltage measured is used to calculate current flowing.

What errors does the input resistance of the voltmeter introduce into the determination of current?

2. Relevant equations
I don't know whether this is useful or not but:

$$Input resistance = Z = R_{Test}\frac{V_{2}}{\left(V_{1}-V_{2}\right)}$$

3. The attempt at a solution
Well, my idea is that it won't introduce any error since both voltage and resistance are measured with the input resistance of the voltmeter in place.

When the values are used to calculate current, the 'errors' associated with voltage and resistance would cancel out. I cannot proof it mathematically though.

Thanks in advance for any suggestion!