AP Physics C: Electricity and Magnetism Review Guide

AP Physics C: E&M covers the same electricity and magnetism as AP Physics 2, but expresses it using calculus (derivatives and integrals). The laws are more abstract but also more elegant and powerful.

Exam structure

• 3 hours total (same format as Physics C: Mechanics).
• Section I: 35 multiple choice (split no-calc and calc).
• Section II: 3 free response (split no-calc and calc).

Unit 1: Electrostatics

Gauss's law and electric fields

• Gauss's law: closed integral of E times dA equals Q enclosed slash epsilon 0. Find electric fields from symmetric charge distributions.
• Electric potential: V equals minus integral of E dot dl. Relates field to potential.
• Capacitors: C equals Q slash V. Parallel plate: C equals epsilon 0 A slash d.

Unit 2: Conductors and Dielectrics

Inside a conductor in equilibrium: E equals 0. All charge resides on surface. Dielectrics increase capacitance.

Unit 3: Electric Circuits

• Ohm's law: V equals I R. Power: P equals I V.
• Kirchhoff's rules: currents sum to zero at junctions. Voltages sum to zero in loops.
• RC circuits: Q(t) equals Q max (1 minus e to the minus t slash (RC)). Time constant tau equals RC.

Unit 4: Magnetism and Ampere's Law

Magnetic fields from currents

• Ampere's law: closed integral of B times dl equals mu 0 I enclosed. Find magnetic fields from symmetric current distributions.
• Long straight wire: B equals mu 0 I slash (2 pi r).
• Solenoid: B equals mu 0 n I (where n is turns per unit length).

Unit 5: Electromagnetic Induction

Faraday's law and Maxwell equations

• Faraday's law: closed integral of E times dl equals minus d(Phi B) slash dt. Changing magnetic flux induces electric field.
• Lenz's law: induced effects oppose the change.
• Self-inductance: EMF equals minus L d I slash dt.
• Maxwell's equations unify electricity and magnetism into four laws.

How to score a 5

1. Gauss's law simplifies many problems. Use it whenever there is symmetry.
2. Faraday's law appears on every exam. Recognize scenarios where flux changes and predict induced fields.
3. Understand Ampere's law. It is the magnetic analog of Gauss's law.
4. Know RC and LC circuits: time constants and oscillation frequencies.
5. The minus sign in Faraday's law is Lenz's law. Do not forget it.