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 $10^{-3} \, ^\circ C$.

$A$ moving coil galvanometer has $100$ turns and each turn has an area of $2.0 \,cm^2$. The magnetic field produced by the magnet is $0.01 \,T$ and the deflection in the coil is $0.05$ radian when a current of $10 \,mA$ is passed through it. The torsional constant of the suspension wire is $x \times 10^{-5} \,N-m / rad$. The value of $x$ is . . . . . . .

To make the magnetic field radial in a moving coil galvanometer:

$A$ galvanometer having a coil resistance of $30\,\Omega$ shows full-scale deflection when a current of $2\,A$ passes through it. It can be converted into an ammeter to read currents up to $10\,A$ by:

The resistance of a galvanometer is $50\,\Omega$ and the current required to give full-scale deflection is $100\,\mu A$. In order to convert it into an ammeter reading up to $10\,A$,it is necessary to put a resistance of

$A$ $50\,\Omega$ resistance is connected to a battery of $5\,V$. $A$ galvanometer of resistance $100\,\Omega$ is to be used as an ammeter to measure current through the resistance. For this,a resistance $r_s$ is connected to the galvanometer. Which of the following connections should be employed if the measured current is within $1\%$ of the current without the ammeter in the circuit?