The maximum magnetic field produced by a current of 12 A passing through a copper wire of diameter 1.2 mm is

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