A negative charge is coming towards the observer. The direction of the magnetic field produced by it will be (as seen by observer)

Two straight long conductors $AOB$ and $COD$ are perpendicular to each other and carry currents $i_1$ and $i_2.$ The magnitude of the magnetic induction at a point $P$ at a distance $d$ from the point $O$ in a direction perpendicular to the plane $ABCD$ is

The magnetic induction at the point $O,$ if the wire carries a current $i,$ is

The figure below shows a current loop having two circular arcs joined by two radial lines. The magnetic field at $O$ is