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 $2.4 \times 10^{-3} \mathrm{~m}^2$ and $4.8 \times 10^{-3} \mathrm{~m}^2$ respectively, then the ratio of the current sensitivities of the galvanometer $A$ and $B$ is

If a wire of length ' $L$ ' carrying a current ' $i$ ' is bent in the shape of a semi-circular arc as shown in the figure, then the magnetic field at centre of the arc is

A galvanometer having 30 divisions has a current sensitivity of $0.0625 \frac{d i \nu}{\mu A}$. If it is converted into a voltmeter to read a maximum of 6 V , then the resistance of that voltmeter is

The magnetic field at the centre of a long solenoid having 400 turns per unit length and carrying a current ' $i$ ' is $6.24 \times 10^{-2} \mathrm{~T}$. The magnetic field at the centre of another long solenoid having 200 turns per unit length and carrying a current $\frac{i}{2}$ is