The magnitude of magnetic induction at mid point 'O' due to current arrangement as shown in figure will be ($\mu_0$ = permeability of free space)

A circular loop of radius R is carrying current I. The ratio of magnetic field at the center of circular loop and at a distance R from the center of the loop on its axis is

A wire carrying current 'I' along x axis has length 'L' and it is kept in a magnetic field $B(\hat{i}+2\hat{j}-2\hat{k})$ T. The magnitude of magnetic force acting on the wire is

A charged particle is moving in a uniform magnetic field in a circular path of radius 'R'. When the energy of the particle becomes 3 times the original, the new radius will be