The ratio of the magnetic field at the centre of a current-carrying coil of radius $a$ to the magnetic field at a distance $a$ from the centre of the coil along its axis is

$A$ charged particle $A$ with charge $q = 2 \, C$ has a velocity $v = 100 \, m/s$. When it passes through point $A$ with the velocity in the direction shown in the figure,the strength of the magnetic field at point $B$ due to this moving charge is ....... $\mu T$ $(r = 2 \, m)$.

$N$ 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 small segment. The difference between enclosed currents,$I_A - I_B$,for the given Amperian loops is

In the diagram,$I_{1}$ and $I_{2}$ are the strengths of the currents in the loop and straight conductor,respectively. Given $OA = AB = R$. The net magnetic field at the centre $O$ is zero. Then the ratio of the currents in the loop and the straight conductor is:

The magnetic field intensity at the centre of a circular wire of radius $0.1 \,m$ carrying a current of $0.2 \,A$ is:

Give two different properties of a current-carrying coil and state Ampere's suggestion.