$A$ long straight wire carries a current of $18 \,A$. The magnitude of the magnetic field at a point $12 \,cm$ from it is

Two similar coils are kept mutually perpendicular such that their centres coincide. At the centre,find the ratio of the magnetic field due to one coil and the resultant magnetic field by both coils,if the same current is flowing through them.

The figure below shows three circuits consisting of concentric circular arcs and straight radial lines. The center of the circle is shown by the dot. The same current flows through each of the circuits. If $B_1, B_2, B_3$ are the magnitudes of the magnetic field at the center, which of the following is true?

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

$A$ current passing through a circular coil of two turns produces a magnetic field $B$ at its centre. The coil is then rewound so as to have four turns and the same current is passed through it. The magnetic field at its centre now is

Consider the magnetic field produced by a long straight current-carrying wire.