Which of the following gives the value of the magnetic field according to Biot-Savart's law?

In the figure,what is the magnetic field at the point $O$?

The magnetic field induction at the centre of a circular coil of radius $5 \,cm$ carrying a current of $0.9 \,A$ is (in $SI$ units) (where $\varepsilon_0$ is the absolute permittivity of air in $SI$ units, and the velocity of light $c = 3 \times 10^8 \,ms^{-1}$):

Which of the following graphs represents the variation of magnetic field $B$ with perpendicular distance $r$ from an infinitely long,straight conductor carrying current?

Figures $A$ and $B$ show two long straight wires of circular cross-section (radii $a$ and $b$ with $a < b$),each carrying a current $I$ which is uniformly distributed across the cross-section. The magnitude of the magnetic field $B$ varies with radial distance $r$ from the axis. Which of the following graphs correctly represents the variation of $B$ with $r$ for both wires?

Two long straight wires,each carrying a current $I$ in opposite directions,are separated by a distance $R$. The magnetic induction at a point midway between the wires is