How does ammeter measures the current{Working of ammmeter}?

Dear amarnath

to understand the workinf principle of ammeter or voltmeter first you should learn the galvanometer

The galvanometer is the main component in analog ammeters and voltmeters.Figure illustrates the essential features of a common type called the  D’Arsonval galvanometer.

It consists of a coil of wire mounted so that it is free to rotate on a pivot in a magnetic field provided by a permanent magnet. The basic op-eration of the galvanometer makes use of the fact that a torque acts on a current loop in the presence of a magnetic field . The torque experienced by the coil is proportional to the current through it: the larger the current, the greater the torque and the more the coil rotates before the spring tightens enough to stop the rotation. Hence, the deflection of a needle attached to the coil is proportional to the current. Once the instrument is properly calibrated, it can be used in conjunction with other circuit elements to measure either currents or potential differences.

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Badiuddin

can we use series resisters as a voltmerter? Why the volmeter have high resistance?