Question

What is the least count of galvanometers?

Answer 1

In order to solve this question we need to understand the least count of any device. Least count of any device is the smallest measurement which a device can measure and this least count can be used to measure how much zero error a device has.Zero error must not be confused with error due to Heisenberg uncertainty principle because Heisenberg uncertainty principle is an inherent error at micro level while zero error is mechanical error of a device. For example, the least count of a Vernier caliper is in millimeters typically of order of $0.1mm$ which indicates that this device can measure up to millimeters.

Complete answer:
Galvanometer is an electronic device consisting of large resistance and a deflector which deflects on both sides about mean position. A Galvanometer is used to measure small currents in a circuit by deflecting the deflector about mean position.

Least count exists for any device only when it measures something but since galvanometer does not measure anything rather it is just used to detect small currents in circuit so an ideal galvanometer does not have least count. However the galvanometer could be converted into an ammeter which can measure up to microampere current.

Hence, the least count of ammeters made from the galvanometer is $0.1\mu m$.

Note: It should be remembered that although an ammeter can be made using a galvanometer, these two are different from each other. Ammeter measures current in circuit while galvanometer just detects the current in circuit. Both have a similarity that both use a low resistance in series so that very high current passes. Modern galvanometers use an amplifier to amplify the small current in the circuit so that it can measure well.