A charge $Q$ is uniformly distributed over the surface of nonconducting disc of radius $R$. The disc rotates about an axis perpendicular to its plane and passing through its centre with an angular velocity $\omega$. As a result of this rotation a magnetic field ofinduction $B$ is obtained at the centre of the disc. If we keep both the amount of charge placed on the disc and its angular velocity to be constant and vary the radius of the disc then the variation of the magnetic induction at the centre of the disc will be represented by the figure

A current loop consists of two identical semicircular parts each of radius $R,$ one lying in the $x-y$ plane and the other in $x-z$ plane. If the current in the loop is $i.$ The resultant magnetic field due to the two semicircular parts at their common centre is

Two identical coils of radius $R$ and number of turns $N$ are placed perpendicular to each others in such a way that they have common centre. The current through them are $I$ and $I\sqrt 3$ . The resultant intensity of magnetic field at the centre of the coil will be  (in $weber/m^2)2$

In the figure, find out the magnetic field at $B$ (Given $I =2.5 \;A,r =5\, cm )$

Magnetic field intensity at the centre of coil of $50$ $turns$, radius $0.5\, m$ and carrying a current of $2\, A$ is

For the magnetic field to be maximum due to a small element of current carrying conductor at a point, the angle between the element and the line joining the element to the given point must be.......$^o$