Which property relates to a fluid that can undergo a dramatic change in its viscosity when exposed to an electric field?

• A. Electro-rheostatic
• B. Magnetorheological
• C. Newtonian
• D. Viscosity

Answer: (A)

When a fluid’s viscosity can change dramatically in response to an electric field, we’re talking about electro-rheostatic (electrorheological) behavior. In these fluids, the dispersed particles become polarized by the electric field and form chain-like structures that span the fluid. This network heavily resists flow, so the apparent viscosity can rise by orders of magnitude, sometimes producing a solid-like state under the field. Once the field is removed, the structures dissipate and the fluid returns to its low-viscosity state, usually very quickly.

This is different from magnetorheological fluids, which respond to magnetic fields, and from Newtonian fluids, whose viscosity remains essentially constant regardless of any field. The key idea is that the electric field actively changes the fluid’s internal structure to change how easily it flows.