Applying Gauss' Law correctly involves finding the charge enclosed by a surface, which often involves a charge density.

Consider, for instance, a sheet of charge with a uniform charge density s.

The sheet is then broken into two pieces. Piece A represents 3/4 of the original sheet and has charge density s_{A}. Piece B is the other 1/4 of the sheet, with charge density s_{B}.

Rank these three charge densities from largest to smallest.

- s = s
_{A}= s_{b} - s > s
_{A}> s_{B} - s
_{B}> s_{A}> s - s > s
_{A}= s_{B} - some other order

The charge densities are all the same. Piece A has 3/4 of the original charge in 3/4 of the original area, so the charge/area is the same as that of the whole sheet. A similar argument applies to piece B.