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

$A$ battery is connected between two points $A$ and $B$ on the circumference of a uniform conducting ring of radius $r$ and resistance $R$. One of the arcs $AB$ of the ring subtends an angle $\theta$ at the centre. The value of the magnetic induction at the centre due to the current in the ring is

$A$ moving charge can produce which field? Explain.

$A$ straight conductor of length $32 \,cm$ carries a current of $30 \,A$. Magnetic induction at a point in air at a perpendicular distance of $12 \,cm$ from the mid-point of the conductor is (in $G$)

An electron revolves around a nucleus with rotational frequency $f$ in a circular orbit. Due to this,the magnetic induction produced at the nucleus position is $B$. The radius of the circular orbit is directly proportional to:

$A$ wire carrying current $i$ is shaped as shown. Section $AB$ is a quarter circle of radius $r$. The magnetic field at the center $C$ is directed: