AP Physics C E and M 8.5: Electric Flux
Describe electric flux through an arbitrary area or geometric shape using the electric field, area vector, and surface orientation.
- Syllabus
- Effective Fall 2025
- Course
- AP Physics C: Electricity & Magnetism
Describe electric flux through an arbitrary area or geometric shape using the electric field, area vector, and surface orientation.
A very large nonconducting slab with a uniform positive volume charge density ρ0 is fixed with the origin of the x y z-axes at its center, as shown in the figure above. The thickness of the slab is d, the length is L, and the width is W, where L≫d and W≫d. The large faces of the slab are parallel to the x y-plane.
Consider a Gaussian cylinder with a cross-sectional area A and height h that is positioned with its axis along the z-axis, as shown in the figure below.

Note: Figures not drawn to scale.
Use Gauss's law to derive expressions for the following. Express your answers in terms of ρ0,A,d,h,z, and physical constants, as appropriate.
Derive an expression for the total flux Φ through the Gaussian surface shown.
2 points
For using Gauss's law to calculate the electric flux 1 point
Φ=ε0Q=ε0ρV
For a correct answer 1 point
Φ=ε0ρ0Ah