Hello,

The flux of a vector field along a surface area is the amount of whatever the field represents passing through the area. The total flux depends on strength of the field, the size of the surface area it passes through, and on how the area is aligned with respect to the field. The flux through a given surface can be positive or negative, because the cosine can be positive or negative. The flux through a closed surface is positive if there is a net outward flow.

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