A circular coil ‘$A$’ has a radius $R$ and the current flowing through it is $I$. Another circular coil ‘$B$’ has a radius $2R$ and if $2I$ is the current flowing through it, then the magnetic fields at the centre of the circular coil are in the ratio of (i.e.${B_A}$ to ${B_B}$)

A coil carrying a heavy current and having large number of turns mounted in a $N-S$ vertical plane and $a$ current flows in clockwise direction. A small magnetic needle at its cente will have its north pole in

What will be the resultant magnetic field at origin due to four infinite length wires. If each wire produces magnetic field '$B$' at origin

When equal current is passed through two coils, equal magnetic field is produced at their centres. If the ratio of number of turns in the coils is $8: 15$, then the ratio of their radii will be

What is the magnetic field at a distance $R$ from a coil of radius $r$ carrying current $I$ ?

A regular polygon of $6$ sides is formed by bending

a wire of length $4 \pi$ meter. If an electric current of $4 \pi \sqrt{3} \mathrm{~A}$ is flowing through the sides of the polygon, the magnetic field at the centre of the polygon would be $x \times 10^{7} \mathrm{~T}$. The value of $\mathrm{x}$ is______.