Surface Waves Generated on Electrolytes by a Traveling Electromagnetic Force

Abstract

This paper presents an experimental study of gravity-capillary waves generated at the free surface of a thin-film of electrolyte ($\text {NaHCO}_3$) due to the presence of an electromagnetic force created by the interaction of a direct electric current and a traveling magnetic field.The field is generated by a permanent magnet moving in straight line, localized externally to the bottom wall of the fluid container. The dominant component of the magnetic field is perpendicular to the plane of the fluid surface in equilibrium. The current is applied transversely to the motion of the magnet through a pair of parallel electrodes, in such a way that the force points either in favour or against the motion of the magnet, depending on the polarity of the electrodes and the magnet orientation. A vertical force component is also generated near the edges of the magnet. It is shown that the electromagnetic force acts as an obstacle for the flow (a magnetic obstacle) and, similarly to a moving solid object, it is able to generate a stationary wave pattern. This patten is reconstructed by optical methods for several magnet velocities. Differences produced by the force acting in favour or against the magnet motion are discussed.