A coil of '$$n$$' turns and radius '$$R$$' carries a current '$$I$$'. It is unwound and rewound again to make another coil of radius $$\left(\frac{\mathrm{R}}{3}\right)$$, current remaining the same. The ratio of magnetic moment of the new coil to that of original coil is

An electron makes a full rotation in a circle of radius $$0.8 \mathrm{~m}$$ in one second. The magnetic field at the centre of the circle is $$\left(\mu_0=4 \pi \times 10^{-7}\right.$$ SI units)

$$\mathrm{A}, \mathrm{B}$$ and $$\mathrm{C}$$ are three parallel conductors of equal lengths and carry currents I, I and 2I respectively as shown in figure. Distance $$A B$$ and $$B C$$ is same as '$$d$$'. If '$$F_1$$' is the force exerted by $$\mathrm{B}$$ on $$\mathrm{A}$$ and $$\mathrm{F}_2$$ is the force exerted by $$\mathrm{C}$$ on $$\mathrm{A}$$, then

The magnetic moment of a current (I) carrying circular coil of radius '$$r$$' and number of turns '$$n$$' depends on