Question

what is the Resistance of constant voltmeter and how explain

Answer 1

A constant current is passed through the resistance under test and the digital multimeter measures the resulting voltage across the resistance as shown in the following figure.

With a known current source and measured voltage, the digital multimeter can determine resistance using Ohm's Law VM = Is *R.

Answer 2

Obviously, the higher the voltmeter resistance, the less loading of the circuit under test, and that is why an ideal voltmeter has infinite internalresistance. ... On the 1000 volt scale, the total resistance is 1 MΩ (999.5 kΩ + 500Ω), giving 1,000,000 Ω per 1000 volts of range, or 1000 ohms per volt (1 kΩ/V).