A long wire carrying a steady current is bent into a circular loop of one turn. The magnetic field at the centre of the loop is B. It is then bent into a circular coil of n turns. The magnetic field at the centre of this coil of n turns will be

A square loop ABCD carrying a current $$i$$, is placed near and coplanar with a long straight conductor XY carrying a current $$I$$, the net force on the loop will be

A long straight wire of radius $$a$$ carries a steady current $$I$$. The current is uniformly distributed over its cross-section. The ratio of the magnetic fields B and B', at radial distance $${a \over 2}$$ and 2$$a$$ respectively, from the axis of the wire is

A proton and an alpha particle both enter a region of uniform magnetic field B, moving at right angles to the field B. If the radius of circular orbits for both the particles is equal and the kinetic energy acquired by proton is 1 MeV, the energy acquired by the alpha particle will be