The ammeter is refitted into a voltmeter in series with a large resistor to divide the voltage. Why can it become a voltmeter? What is the meaning of the value measured by the ammeter? How to calculate the voltage with this value?

The ammeter is refitted into a voltmeter in series with a large resistor to divide the voltage. Why can it become a voltmeter? What is the meaning of the value measured by the ammeter? How to calculate the voltage with this value?

Ammeter and voltmeter are made of the same principle, but because the ammeter is connected in series with the circuit, its resistance is very small relative to the resistance of the electrical appliances in the circuit, which can be ignored. So when calculating, the resistance and current at both ends of the ammeter are ignored (equivalent to short circuit)