AP Physics C: Electricity and Magnetism / Unit 8: Electric Charges, Fields, and Gauss's Law
8.5 Electric Flux
Notes
$$\Phi_E=\int\vec E\cdot d\vec A$$
- For a uniform field and flat surface: $\Phi_E=EA\cos\theta$.
- Field lines entering a closed surface count negative; leaving count positive.
Practice
$E=100$ N/C perpendicular through 0.2 m². Flux:
$EA$.
A surface parallel to the field has flux:
$\cos90°=0$.
The net flux through a closed surface with no charge inside:
What enters also leaves.
Ready for more? Take the Unit 8 test.