Voltmeter range

A voltmeter is an instrument for measuring voltage.

It consists of permanent magnets, coils, etc. The voltmeter is a considerable resistance, which is considered as an open circuit in an ideal situation. The voltmeter ranges commonly used in junior middle school laboratories are 0~3V and 0~ 15V.

The traditional pointer voltmeter includes a sensitive ammeter with a permanent magnet in it, and a coil composed of wires is connected in series between its two ends. The coil is placed in the magnetic field of the permanent magnet and connected with the pointer of the instrument through the transmission device. Most voltmeters are divided into two ranges.

Voltmeter principle

Both pointer voltmeter and ammeter are based on one principle, that is, the magnetic effect of current. The greater the current, the greater the magnetic force, and the greater the swing of the pointer of the display voltmeter. There is a magnet and a coil in the voltmeter. When the coil is energized, it will generate a magnetic field, and when energized, the coil will deflect under the action of a magnet. This is the meter head part of the ammeter.

Because the voltmeter should be connected in parallel with the measured resistance, if the sensitive ammeter is directly used as the voltmeter, the current in the meter will be too large, which will burn out the ammeter. At this time, it is necessary to connect a large resistor in series in the internal circuit of the voltmeter. After this transformation, when the voltmeter is connected in parallel in the circuit again, most of the voltage applied at both ends of the ammeter will be shared by the series resistance due to the effect of the resistance.