In a thin rectangular metallic strip a constant current $I$ flows along the positive  x-direction, as shown in the figure.  The length, width and thickness of the strip are  l, w and d respectively.
A uniform magnetic field  $\overrightarrow{B}$ is applied on the strip along the positive  y-direction.  Due to this, the charge carriers experience a net deflection along the  z-direction.  This results in accumulation of charge carriers on the surface  PQRS and appearance of equal and opposite charges on the face opposite to  PQRS.  A potential difference along the  z-direction is thus developed.  Charge accumulation continues until the magnetic force is balanced by the electric force.  The current is assumed to be uniformly distributed on the cross section of the strip and carried by electrons.