An electron is moving in a circular path under the influence of a transverse magnetic field of 3.57 $$ \times $$ 10^-2 T. If the value of e/m is 1.76 $$ \times $$ 10¹¹ C kg^$$-$$1, the frequency of revoluation of the electron is

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 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 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