$A$ 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:

The ratio of the magnetic field at the center of a current-carrying circular coil of radius $R$ to the magnetic field at a distance of $x = \frac{3R}{4}$ from the center on its axis is:

$PQRS$ is a square loop made of uniform conducting wire. If the current enters the loop at $P$ and leaves at $S$, then the magnetic field will be

What should be the current $i$ (in $A$) in a circular coil of radius $5\,cm$ to annul the horizontal component of Earth's magnetic field ${B_H} = 5 \times {10^{ - 5}}\,T$?

$A$ thin rod is bent in the shape of a small circle of radius $r$. If the charge per unit length of the rod is $\sigma$,and if the circle is rotated about its axis at the rate of $n$ rotations per second,the magnetic induction at a point on the axis at a large distance $y$ from the centre is

$A$ non-planar loop of conducting wire carrying a current $I$ is placed as shown in the figure. Each of the straight sections of the loop is of length $2a$. The magnetic field due to this loop at the point $P(a, 0, a)$ points in the direction: