What are the disadvantages of using ammeter and voltmeter?
The disadvantage of using a voltmeter and ammeter on circuit measurements is that internal burden in both these instruments can affect circuit operation so much as to make a measurement useless.
An ammeter can be converted into a voltmeter by connecting a resistor in series with it. This works best if the ammeter is a very sensitive ammeter, such as in the micro ampere range. More commonly, a voltmeter (or sensitive ammeter) is converted into an ammeter by placing a small resistor in parallel with it.
What would happen when the ammeter is placed in parallel and the voltmeter in series with the circuit at the same time?
If the voltmeter was ahead of the ammeter, the voltmeter would read supply voltage, and the ammeter would read current through the voltmeter, a very small reading. If the ammeter was ahead of the voltmeter, the ammeter would read supply current, which is probably many times in excess of the ammeter's rating, so you would either destroy the ammeter (or battery) or blow its fuse. It does not matter about the voltmeter, as the ammeter is now blown.
An ammeter measures current while a voltmeter measures voltage An ammeter is always connected in series while a voltmeter is connected in parallel To convert a galvanometer into an ammeter, a shunt (very small resistance) must be connected parallel to the galvanometer coil. To convert a galvanometer into a voltmeter, a large resistance must be connected in series with the galvanometer coil.
An ammeter should not be used as a voltmeter. An ammeter is a low impedance device that measures the current going through a circuit, often by measuring the small voltage across a known resistance. A voltmeter is a high impedance device that measures the voltage across a circuit. If you were to connect an ammeter as if it were a voltmeter, you would effectively short out the circuit, drastically affecting its operation, and potentially damaging both the circuit and the ammeter.