What happen when Measure the voltage of a capacitor
it would discharge the capacitor according to the input impedance of the meter. the higher the input impedance, the less the meter will discharge the capacitor.
depends on what you use to measure, but yes, it will only produce a very small amount. a modern dvm could have an input resistance of 10 meg ohms taking 1.2 microamperes from the battery. an old analog meter will take more.
An ideal voltmeter has infinite impedance and will not discharge the plug. In reality, most meters have a finite input impedance and discharge a capacitor, but it is a meter impedance and the capacitor value how long the discharge lasts
The capacitor will be discharged. it depends on what is called the input impedance of the meter. if it is very high, like a digital counter, the effect will be a slower discharge. if the meter is a voice coil meter, the capacitor will discharge faster. the meter measures the voltage by passing current through a resistor or the meter coil in the case of a voice coil meter.
when measuring things must not forget that the act of measuring changes the amount measured. For example, if one measures the voltage across a capacitor of 100 uf with an input impedance of 1 Megaohm, the voltage variation caused by the measurement is negligible. the situation is totally different if we try to measure the voltage across a capacitor of 1 picofarad with the same instrument.
all analog voltmeters have a finite resistance, ranging from 200 mocroamp to a few ma, which determine their fsd current. this resistor will naturally discharge the capacitor, even to a small extent, depending on the value of the capacitance and the measurement voltage.
Electronic voltmeters have a very high equivalent resistance and the effect will be relatively small. Electrostatic voltmeters will have virtually no effect on capacitors because they consume virtually no current. However, the term is practically important.