AP Physics 2 Unit 10 Cheatsheet: Electric Force, Field, and Potential

Fundamental Properties:

• Charge is positive or negative; elementary charge e is smallest indivisible unit
• Electron: −e; Proton: +e; Neutron: 0
• Point charge model: physical size negligible in context

Coulomb's Law:

Force Direction:

• Same sign → repulsive
• Opposite sign → attractive
• Force parallel to line of separation

Electric Permittivity (ε): Measures how easily a material becomes polarized by external field.

Polarization: Induced rearrangement of electrons → separation of + and − charges within material.

Free space: ε₀ (constant); Matter: ε = κε₀ > ε₀ for a dielectric (depends on composition and how readily the material polarizes, i.e., its dielectric constant κ).

Conductors vs. Insulators:

• Conductors: Charge carriers move easily; excess charge on surface only (equilibrium)
• Insulators: Charge carriers cannot move easily; excess charge stays where it is deposited (can remain in the interior as well as on the surface) rather than redistributing

Equipotential lines (isolines): Lines of equal electric potential.

Key relationships:

• Isolines perpendicular to field vectors
• No field component along isoline
• Field points toward decreasing potential
• Field magnitude = potential gradient

Constructing maps: Derive field map from equipotential map and vice versa.

Solving strategy: Use equipotential maps to visualize field direction and predict charged particle motion.