A ‐shaped wire of mass and length is immersed with its two ends in mercury (see figure). The wire is in a homogeneous field of magnetic induction . If a charge, that is, a current pulse , is sent through the wire, the wire will jump up.

If the wire reaches height , calculate the magnitude of the charge or current pulse, assuming that the time of the current pulse is very small in comparison with the time of flight. Make use of the fact that impulse of force equals , which equals . Evaluate for gm, cm & meters.