Consider the following two statements $A$ and $B$ and identify the correct choice given in the answers.
$A$. Duddell's thermo-galvanometer is suitable to measure direct current only.
$B$. Thermopile can measure temperature differences of the order of $10^{-3} \, ^\circ C$.

$STATEMENT-1$: The sensitivity of a moving coil galvanometer is increased by placing a suitable magnetic material as a core inside the coil.
$STATEMENT-2$: Soft iron has a high magnetic permeability and cannot be easily magnetized or demagnetized.

There are three voltmeters of the same range but of resistances $10000\,\Omega$,$8000\,\Omega$,and $4000\,\Omega$ respectively. The best voltmeter among these is the one whose resistance is ................ $\Omega$.

Two moving coil galvanometers $A$ and $B$ having identical springs are placed in magnetic fields of $0.25 \ T$ and $0.5 \ T$ respectively. If the number of turns in $A$ and $B$ are respectively $36$ and $48$,and the areas of the coils $A$ and $B$ are $2.4 \times 10^{-3} \ m^2$ and $4.8 \times 10^{-3} \ m^2$ respectively,then the ratio of the current sensitivities of the galvanometers $A$ and $B$ is

$A$ moving coil galvanometer of resistance $100 \ \Omega$ shows a full scale deflection for a current of $1 \ mA$. The value of shunt resistance required to convert this galvanometer into an ammeter, showing full scale deflection for a current of $5 \ mA$, is . . . . . . $\Omega$.

To convert a $800\, mV$ range millivoltmeter of resistance $40\,\Omega$ into an ammeter of $100\, mA$ range,the resistance to be connected as a shunt is .............. $\Omega$.