Current Sensitivity of Galvanometer: How it can be increased

We define current sensitivity of galvanometer as the current, in microamperes, needed to generate one millimeter (1mm) deflection on a scale placed or positioned one meter away (1m) from the mirror of the galvanometer (an electrical gadget used to calculate the passage of current through a electric circuit).

OR

The angular twist per unit current is called current sensitivity of galvanometer.

Mathematically,


Sensitivity = šš¹ / I = BAN / C


How to make galvanometer more sensitive.

▶ By increasing the number of turns of the coil N, but if it is increased/enhanced beyond a certain limit then the coil become heavy.

▶ By boosting magnetic flux density B, placing or adjusting the soft iron cylinder inside the coil. This alternation is very effective to enhance the sensitivity.

▶ By increasing the area A but it can make the coil bulky and uncontrollable.

▶ By decreasing C, a suspension wire should have large length and small radius.

Dead Beat Galvanometer

A sensitive coil is not stable; its coil oscillates many times before coming to rest, although the current through the coil is stopped. But in some galvanometers the coil comes to rest very soon, as the current stops to flow/pass through it.

A galvanometer, in which the coil comes to rest fastly after passage of current through it, is called stable or dead beat galvanometer.

How to make a Galvanometer Dead Beat

When current passes through the coil it starts rotating about central axis. The flux through frame of coil changes so (by Faraday's law) an emf.and hence a (eddy) current is induced in the frame which opposes it cause (i.e. the rotation of coil). In this way the oscillations are damped.

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