The sensitiveness of a moving coil galvanometer can be increased by decreasing:

$A$ galvanometer of resistance $50 \Omega$ gives a full-scale deflection for a current of $5 \times 10^{-4} \text{ A}$. The resistance that should be connected in series with the galvanometer to read $3 \text{ V}$ is: (in $Omega$)

When a shunt resistance of $4r$ is connected to a galvanometer,it becomes an ammeter that can measure $0.03 \, A$. When a shunt resistance of $r$ is connected to the same galvanometer,it becomes an ammeter that can measure $0.06 \, A$. What is the current capacity $(i_g)$ of the galvanometer in $A$?

$A$ multirange voltmeter can be constructed by using a galvanometer circuit as shown in the figure. We want to construct a voltmeter that can measure $2 \ V$,$20 \ V$,and $200 \ V$ using a galvanometer of resistance $10 \ \Omega$ that produces maximum deflection for a current of $1 \ mA$. Find $R_1$,$R_2$,and $R_3$ that have to be used.

Why is the total resistance of a voltmeter kept very high?

Assertion : The sensitivity of a moving coil galvanometer is increased by placing a suitable magnetic material as a core inside the coil.
Reason : Soft iron has high magnetic permeability and cannot be easily magnetized or demagnetized.