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As shown in the right figure, an infinite slab of charge of thickness 2a is cent

ID: 2139828 • Letter: A

Question

As shown in the right figure, an infinite slab of charge of thickness 2a is centered in xy-plane.        The charge density is ? = ?0(1 - |z|/a).        Find the electric field strengths (16 points)         

As shown in the right figure, an infinite slab of charge of thickness 2a is centered in xy-plane. The charge density is ? = ?0(1 - |z|/a). Find the electric field strengths inside the slab of charge. outside the slab of charge. [Draw and show the Gauss surface you are using whenever you apply Gauss' law, and explain why you choose it.]

Explanation / Answer

part 1

draw a box enclosing a region inside the slab from -z to z

flux through the 2 surfaces = E x area = charge inside

E x 2 x length of box = (rhonot x length of box x (2z)/a) / epsilonnot

E = (rhonot x z/a) /epsilonnot

part 2

draw a box enclosing whole of the slab and part of the region outside the slab from -z to z

flux through the 2 surfaces = E x area = charge inside

E x 2 x length of box = (rhonot x length of box x (2a)/a) / epsilonnot

E = rhonot / epsilonnot

the surfaces have been taken so because of the symmetry in the problem along the z axis