A bar magnet is inside a closed cubical box. Magnetic field lines pointing outward from the box produce positive flux, and those pointing inward produce negative magnetic flux.
(a) Is the total magnetic flux through the surface of the box positive, negative, or zero?
(b) Choose the best explanation from among the following:
I. There are more outward magnetic field lines because the magnet is inside the box.
II. The magnet draws field lines inward toward itself, producing more negative flux.
III. The same number of magnetic field lines leave the box as enter it.