$A$ tightly wound $100$ turns coil of radius $10 \,cm$ carries a current of $7 \,A$. The magnitude of the magnetic field at the centre of the coil is (Take permeability of free space as $4 \pi \times 10^{-7} \,SI$ units):

The magnetic induction at the centre $O$ of the current-carrying bent wire shown in the adjoining figure is:

The magnetic field at the centre of a current-carrying circular coil is

$A$ current $I$ is flowing along an infinite,straight wire in the positive $Z$-direction,and the same current $I$ is flowing along a similar parallel wire $5 \ m$ apart in the negative $Z$-direction. $A$ point $P$ is at a perpendicular distance of $3 \ m$ from the first wire and $4 \ m$ from the second. What is the magnitude of the magnetic field $B$ at point $P$?

$A$ long wire is bent into a circular coil of one turn and then into a circular coil of smaller radius having $n$ turns. If the same current passes in both the cases,the ratio of magnetic fields produced at the centre for one turn to that of $n$ turns is

Shown in the figure is a conductor carrying a current $I$. The magnetic field intensity at the point $O$ (common centre of all the three arcs) is