A Uniformly Charged Slab. A slab of insulating material has thickness 2$d$ and is oriented so that its faces are parallel to the $y z$ -plane and given by the planes $x=d$ and $x=-d$ . The $y$ -and $z$ -dimensions of the slab are very large compared to $d$ and may be treated as essentially infinite. The slab has a uniform positive charge density $\rho .$ (a) Explain why the electric field due to the slab is zero at the center of the slab $(x=0)$ . (b) Using Gauss's law,find the electric field due to the slab (magnitude and direction) at all points in space.