Question

The sensitivity of a tangent galvanometer increases, if
A. Number of turns decreases
B. Number of turns increases
C. Field increases
D. Number of turns remains same

Answer 1

Hint: Sensitivity of a tangent galvanometer is the ratio of change in deflection to the current responsible for this deflection, which is directly proportional to the torsion constant. The other factors on the sensitivity of a galvanometer depends are the magnetic field, radius or area of the coil and torsion constant of the spring and suspension wire.

Complete step by step answer:
The sensitivity of a tangent galvanometer is defined as the ratio of change in deflection to the current responsible for this deflection.
So sensitivity of a tangent galvanometer is given as,
$S = \dfrac{\theta }{i}$ ... (I)
We know that when the galvanometer gives huge deflection for a small current, it is called as sensitive.

We know that the current is expressed as $I = k\tan \theta $
where $k = \dfrac{{2R{B_{\rm{H}}}}}{{{\mu _0}N}}$ is called the torsion constant.

Substitute the expressions in the equation (I), we have,
$S = \dfrac{\theta }{{\left( {\dfrac{{2\pi {B_{\rm{H}}}}}{{{\mu _0}N}}} \right)\tan \theta }}$
From the above equation, we can say that the sensitivity of a galvanometer is directly proportional to the number of turns in the coil.

Thus, the sensitivity of a tangent galvanometer increases, if the number of turns in the coil increases and option (B) is correct.

Note: The sensitivity of a tangent galvanometer can be increased by increasing the number of turns of the coil, but the value of number of turns cannot be increased beyond a particular limit because that will make the galvanometer heavy, bulky and the resistance of it will increase.