What is the principle of operation of a voltmeter?
A coil is placed in the voltmeter between the poles of the magnet. fixed on the axis. The arrow of the device is attached to it. When electric current flows through the coil, forces from the magnets act on the horizontal sections of the coil wires. On opposite sides of the coil, currents flow in opposite directions, therefore the forces from the side of the magnets are directed oppositely. Under the action of these forces, the coil turns, with it turns relative to the scale of the arrow of the device. The coil spring prevents the coil from turning. The coil stops rotating when the spring force balances the magnetic force. That is, the device of the voltmeter is the same as that of the ammeter, only the scale is calibrated immediately in volts.