The magnetic field at a distance $r$ from a long straight wire carrying current $i$ is $0.4 \ T$. The magnetic field at a distance $2r$ is: (in $T$)

$N$ 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

If a battery of $12 \text{ V}$ is connected across the diametrically opposite points $A$ and $B$ of a conducting ring of radius $R$ and the current drawn from the battery is $I$,then the magnetic field produced at the centre of the ring due to the ring is . . . . . . .

$Weber/m^2$ is equal to

Calculate the magnetic field at point $M$ for the given current distribution.

$A$ long wire carries a steady current. It is bent into a circle of one turn and the magnetic field at the centre of the coil is $B$. It is then bent into a circular loop of $n$ turns. The magnetic field at the centre of the coil for the same current will be