Doubly ionized oxygen atoms $\left({\mathrm{O}}^{2-}\right)$ and singly-ionized lithium atoms $\left({\mathrm{Li}}^{+}\right)$ are travelling with the same speed, perpendicular to a uniform magnetic field. The relative atomic masses of oxygen and lithium are $16$ and $7$ respectively. The ratio $\frac{\text{ radius of }{\mathrm{O}}^{2-}\text{ orbit }}{\text{ radius of }{\mathrm{Li}}^{+}\text{orbit }}$ is

In a region of space, both electric and magnetic field are present simultaneously in opposite directions. A positively charged particle is projected with certain speed an angle $\theta \left(<90°\right)$ with magnetic field. It will move in a

A ring carrying current $I$ lies in $x-z$ plane as shown. A short magnetic dipole with dipole moment directed along $x$-axis is fixed at origin. If the ring is free to move anywhere, then it will