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Reduction Factor of a Galvanometer

The deflexion produced in a galvanometer needle by a given current depends on the ratio H/G, H being the strength of the field in which the needle hangs when undisturbed, and G the strength of the field due to a unit current in the coil. This ratio is known as the reduction factor of the galvanometer. Let us denote it by k, then

and if the instrument be used as a tangent galvanometer we have

if it be used as a sine galvanometer

φ and ψ being the deflexions produced in either case by a current i.

It must be remembered that the reduction factor depends on the strength of the magnetic field in which the magnet hangs as well as on the galvanometer constant There is generally attached to a reflecting galvanometer a controlling magnet capable of adjustment The value of k will accordingly depend on the position of this control magnet, which in most instruments is a bar, arranged to slide up and down a vertical axis above the centre of the coils, as well as to rotate about that axis. The sensitiveness of the instrument can be varied by varying the position of this magnet.



Last Update: 2011-03-15