is determined by the Kutta condition. The circulation on every closed curve around the airfoil has the same value, and is related to the lift generated by each unit length of span. Provided the closed curve encloses the airfoil, the choice of curve is arbitrary. Circulation is often used in computational fluid dynamics as an intermediate variable to calculate forces on an airfoil or other body. Fundamental equations of electromagnetism In electrodynamics, the Maxwell-Faraday law of induction can be stated in two equivalent forms: that the curl of the electric field is equal to the negative rate of change of the magnetic field, or that the circulation of the electric field around a loop is equal to the negative rate of change of the magnetic field flux through any surface spanned by the loop, by Stokes' theorem . Circulation of a static magnetic field is, by Ampère's law, proportional to the total current enclosed by the loop . For systems with electric fields that change over time, the law must be modified to include a term known as Maxwell's correction. See also Maxwell's equations Biot–Savart law in aerodynamics Kelvin's circulation theorem References Fluid dynamics Physical quantities Electromagnetism