The shape of the magnetic field lines due to an infinitely long,straight current-carrying conductor is:

How can we determine the direction of the magnetic field using the Biot-Savart law?

$A$ coil having $9$ turns carrying current $I$ produces a magnetic field $B_1$ at the centre. If the same wire is rewound into a coil of $3$ turns carrying the same current $I$,then the magnetic field at the centre $B_2$ is:

If a positive ion is moving away from an observer with some acceleration,then the lines of force of magnetic induction will be

Two identical coils having the same number of turns and carrying equal current have a common centre,and their planes are at right angles to each other. What is the ratio of the magnitude of the resultant magnetic field at the centre to the magnetic field due to one of the coils at the centre?

The magnetic field at the centre of a circular coil of radius $r$,through which a current $I$ flows,is: