$A$ circular coil carrying a certain current produces a magnetic field $B_{0}$ at its centre. The coil is now rewound so as to have $3$ turns and the same current is passed through it. The new magnetic field at the centre is

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

$A$ wire in the form of a square of side $a$ carries a current $i$. Then, the magnetic induction at the centre of the square is (Magnetic permeability of free space $= \mu_0$)

$A$ 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

$A$ circular current-carrying coil has a radius $R$. The distance from the centre of the coil on the axis where the magnetic induction will be $\frac{1}{8}$th of its value at the centre of the coil is:

$A$ negative charge is moving towards the observer. What will be the direction of the magnetic field produced by it,as seen by the observer?