Does magnetic force act along the line joining the centres like gravitational and electric forces do?
Are the directions of magnetic field and magnetic lines of force the same? I have read that the direction of the field is tangential to the direction of the line of force.
(a) "Does magnetic force act along the line joining the centres [...] ? The centres of what? You need to specify whether the forces are between current-carrying wires or between magnets or something else.
Note that electrostatic and gravitational forces do act along the lines between the centres of spherically symmetrical charge or mass distributions, but this does not hold for every shape of body.
(b) "Are the directions of magnetic field and magnetic lines of force the same?" Yes, a magnetic line of force (or magnetic field line) is defined as a line whose direction at every point along it is the direction of the magnetic field at that point. The direction of the line at a point is the direction of the tangent to the line at the point. There's no difference.
