An infinitely long conductor $PQR$ is bent to from a right angle as shown. A current $I$ flows through $PQR$ . The magnetic field due to this current at the point $M$ is $H_1$ . Now, another infinitely long straight conductor $QS$ is connected at $Q$ so that the current in $PQ$ remaining unchanged. The magnetic field at $M$ is now $H_2$ . The ratio $H_1/H_2$ is given by

An arrangement with a pair of quarter circular coils of radii $r$ and $R$ with a common centre $C$ and carrying a current $I$ is shown in the figure. The permeability of free space is $\mu_0$. The magnetic field at $C$ is

The earth’s magnetic field at a given point is $0.5 \times {10^{ - 5}}\,Wb{\rm{ - }}{m^{ - 2}}$. This field is to be annulled by magnetic induction at the center of a circular conducting loop of radius $5.0\,cm$. The current required to be flown in the loop is nearly......$A$

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

Two insulated circular loop $A$ and $B$ radius ' $a$ ' carrying a current of ' $\mathrm{I}$ ' in the anti clockwise direction as shown in figure. The magnitude of the magnetic induction at the centre will be :

A current $I$ flows around a closed path in the horizontal plane of the circle as shown in the figure. The path consists of eight arcs with alternating radii $r$ and $2r$. Each segment of arc subtends equal angle at the common centre $P.$ The magnetic field produced by current path at point $P$ is