Question

32.1 gauss law for magnetic fields

remember when we draw magnetic field lines, we draw them so that the density of the lines in a given drawing represents the strength of the field at every location in the drawing. therefore, if we draw a surface in a uniform magnetic field

the number of magnetic field lines must equal the number of electric field lines.
the number of magnetic field lines entering the surface must be less than the number leaving the surface.
the number of magnetic field lines entering the surface must be greater than the number leaving the surface.
the number of magnetic field lines entering the surface must be equal to the number leaving the surface.

Explanation:

Gauss' Law for Magnetic Fields states that magnetic monopoles do not exist. Magnetic field lines are continuous and form closed loops. For a surface in a uniform magnetic field, since there are no magnetic monopoles to act as sources or sinks of magnetic field lines, the number of magnetic field lines entering a closed surface must equal the number of magnetic field lines leaving the surface.

Answer:

the number of magnetic field lines entering the surface must be equal to the number leaving the surface.