Here is a problem that emerged some time ago:
We needed to measure the emf(electromotive force) and internal resistance of a car battery. The only instruments were voltmeter and ammeter.
1) the first time connect voltmeter and ammeter in series to the battery and write up the results of the measurements.
2)the second time connect voltmeter and ammeter in parallel to the battery and write up the results of the measurements.
Based on these measurements only, calculate emf $E$ and internal resistance $r$ of the battery. To be specific,
1)for the first case $U_1=10V$ and $I_1=0.1A$
2)for the second case $U_2=1V$ and $I_2=1A$
How do you solve this problem?
Arguably, this method is advanced in the sense that the result do not depend on internal resistances(unknown) of voltmeter and ammeter. This last claim does not seem obvious.
Maybe there is an easy way prove(disprove) this claim!