Question

Obtain the expression for current sensitivity of moving coil galvanometer.

Answer 1

Hint: Galvanometer sensitivity is defined as the current in micro ampere needed to consume a deflection of one millimeter at a scale 1 m away from the mirror. A galvanometer 's sensitivity is greater if the instrument displays greater deflection for a low current value.

Complete step-by-step answer:
If $d\theta$ is the deflection shift corresponding to the small $dI$ shift in the current through a galvanometer, then its current sensitivity is
${S_I} = \dfrac{{d\theta }}{{dI}}$
The deflection $\theta$ is given in moving coil galvanometer as
$\theta = \dfrac{{NAB}}{{dC}}I$
or $\theta = KI$
Where $K = \dfrac{{NAB}}{C}$is a constant meter.
Differentiating the above equation against $I$.
$\dfrac{{d\theta }}{{dI}} = K$
So, ${S_I} = K = \dfrac{{NAB}}{C}$. Thus, the current sensitivity of a moving coil galvanometer with a radial field depends on $N$, $A$ and $B$ and is inversely proportional to $C$.

Note: A galvanometer is a device used to detect or measure the magnitude of small electric current. Typically, the current and its strength are demonstrated by the movement of a magnetic needle, or that of a coil in a magnetic field that is an important part of a galvanometer.

A galvanometer with a moving coil is a device used to measure electrical currents. It is a sensitive electromagnetic device that even of the order of a few microamperes can measure low currents.

Moving-coil galvanometers are divided essentially into two types:
Suspended coil galvanometer
Pivoted-coil or Weston galvanometer

The moving coil galvanometer principle states that when placed in an external magnetic field a current-carrying coil experiences magnetic torque. Owing to the influence of the magnetic torque the angle from which the coil is deflected is proportional to the magnitude of the current in the coil.