A thin circular wire carrying current $I$ has magnetic moment $M$. The shape of the wire is changed to a square and it carries the same current. It will have magnetic moment $M_1$. The ratio $M$ to $M_1$ is

A circular arc of wire of radius of curvature $r$ subtends an angle of $\dfrac{\pi}{5}$ radian at its centre. If current $i$ is flowing in it then the magnetic induction at its centre is ($\mu_0$ = permeability of free space)

A solenoid of 1000 turns is wound uniformly on a glass tube 4 m long and $0.3$ m in diameter. The magnetic intensity at the centre of the solenoid when a current of 4 A flows through it is

A square loop ABCD of side L carrying a current $I_1$ is placed at a distance $(L/3)$ from a conductor coplaner with a straight conductor XY carrying current $I_2$ as shown in figure. The net force on the loop will be ($\mu_0$ = magnetic permeability)