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

Two identical long parallel wires carry currents $I_1$ and $I_2$ such that $I_1 > I_2$. When the currents are in the same direction,the magnetic field at a point midway between the wires is $6 \times 10^{-6} \ T$. If the direction of $I_2$ is reversed,the field becomes $3 \times 10^{-5} \ T$. The ratio $\left(\frac{I_1}{I_2}\right)$ is-

The magnitude of the force per unit length acting on a thin wire carrying a current $I=8 \text{ A}$ at a point $O$, if the wire is bent as shown in the figure with a radius $R=10 \pi \text{ cm}$, is (in $\mu \text{N/m}$)

The radius of a circular coil is $R$ and it carries a current of $I$ ampere. The intensity of the magnetic field at a distance $x$ on the axis from the centre $(x >> R)$ will be:

$Weber/m^2$ is equal to

$N$ equally spaced charges, each of value $q$, are placed on a circle of radius $R$. The circle rotates about its axis with an angular velocity $\omega$ as shown in the figure. $A$ bigger Amperian loop $B$ encloses the whole circle, whereas a smaller Amperian loop $A$ encloses a single charge. The difference between the enclosed currents, $I_A - I_B$, for the given Amperian loops is: