If a current is passed through a spring then the spring will

If in a circular coil $$A$$ of radius $$R,$$ current $$I$$ is flowing and in another coil $$B$$ of radius $$2R$$ a current $$2I$$ is flowing, then the ratio of the magnetic fields $${B_A}$$ and $${B_B}$$, produced by them will be

If an electron and a proton having same momentum enter perpendicular to a magnetic field, then

The time period of a charged particle undergoing a circular motion in a uniform magnetic field is independent of its