Question

For an open surface, which statement correctly describes the area vector convention?

Options

• The outward normal must always be chosen

• Both normals give the same flux value

• Either normal direction may be chosen, but the choice must remain consistent

• The inward normal must always be chosen

Answer 1

For an open surface, the direction of the area vector can be chosen arbitrarily as either of the two possible normals. However, once a choice is made, it must be applied consistently throughout the calculation. This is different from closed surfaces, where the outward normal is mandatory.