The Guide to AP Physics C: E&M

By Mia Hanuska

Rule number one of AP Physics C Electricity and Magnetism: no matter how prepared you think you are, you’re not prepared enough. This is the second semester course of AP Physics C, and because everything is at a molecular level, literally nothing will make sense. Almost all logic goes out the window and despite thinking you’ll get a fresh start and be free from Mechanics, you will soon learn that Mechanics somehow finds its way into this course. Like Physics C: Mechanics, this class will require extreme self-studying, and many topics will require lots of time outside of class to understand thoroughly enough for the AP test. 

Overview

AP Physics C: E&M has six units, and is a slightly faster pace than semester 1. When I took the course, we spent almost two class periods on the entire last unit, so you’ll likely have to self-study it as well. Unit Tests are each month (E&M units contain more material than Mechanics units) but unlike Mechanics, units build upon each other. Concepts you spend lots of time on at the beginning are nearly identical to those of later units, which is helpful.

General Study Resources

  • Watch the AP classroom videos, they teach the basics of all the topics you’ll need to know. They also help you understand what will/won’t be on the test
  • Youtube videos will be your best friend, but some channels are better than others. These are the ones I found most helpful:
  • Utilize AP Classroom: complete the subunit quizzes Tandon assigns. Not only do they give you experience with AP questions, they also tell you exactly what sort of questions will be asked (sometimes the videos/Tandon don’t cover everything)
  • For example practice questions: APStudy.net

Unit 1: Electric Fields

In this unit, you get the very beginning of E&M, which makes it one of the hardest units, in my opinion. There’s a lot of new concepts and formulas, and this unit is extremely calculus heavy. 

Topic of Importance: Electric Fields of Charge Distribution

  • Straight line 
  • Ring (from center and from a distance from the center)
  • Arc

Study Help:

Tips:
  • ∫ E ᐧ dA = q/𝜖
  • Electric fields come out of positive charges, and go into negative charges

Practice Problems:

  • 2022 FRQ Sets 1 & 2: Question 1 (a) through (c)
  • 2025 FRQ Question 1

Unit 2: Electric Potential

This unit, you’ll need to understand the relationship between electric fields and electric potential. It’s a short unit, but if I remember correctly, Tandon combines lots of topics into this one unit, which complicates it more. 

Tips: 
  • Positive charges move from higher to lower potential
  • Negative charges move from lower to higher potential

Practice Problems:

  • 2024 FRQ Sets 1 & 2: Question 1
  • 2022 FRQ Sets 1 & 2: Question 1 (d) through (e)

Unit 3: Conductors and Capacitors

To be honest, I hardly studied this unit, but don’t be like me. Capacitors make up a large portion of tests and for some reason CollegeBoard loves using them for both MCQs and FRQs

Topic of Importance: Capacitors

  • Relationship with charge & electric potential
  • Potential Energy
  • Characteristics of its behavior

Study Help:

Tips:
  • If not specified, the dielectric constant is 1
    • If specified, dielectric constant will almost always be >1
  • Once steady-state has been reached, capacitors act as a current-carrying wire

Practice Problems:

  • 2023 FRQ Set 1 Question 3 (d)

Unit 4: Electric Circuits

This unit has a LOT of content. Like, a LOT. Unfortunately, it’s also a large part of the AP test, and thus requires lots of studying. 

Topic of Importance: Resistors & Capacitors

  • Relationship between both (RC circuits)
  • Behavior of current through resistors vs capacitors
  • Potential difference over resistors vs capacitors

Study Help:

Tips:
  • Energy dissipated: ∫ IΔV
  • Memorize the equation: V(t) = ε(e^(-t(1/2RC)))
  • Power dissipated by resistors decreases over time

Practice Problems:

  • 2021 FRQ Sets 1 & 2 Question 1
  • 2023 FRQ Set 1 Question 3
  • 2024 FRQ Sets 1 & 2 Question 2 a) 
  • 2025 FRQ Question 3

Unit 5: Magnetic Fields and Electromagnetism

Good news! A lot of magnetic fields/electromagnetism is the same as electric fields, making this unit a little less difficult than perhaps previously believed. 

Topic of Importance: Ampere’s Law

  • Square & circular loops of wire
  • Using Ampere’s law in other equations

Study Help:

Tips: 
  • Magnetic Flux induces current when either the magnetic field changes OR the area changes
  • F = BIL and F = qvB
  • Flux is at maximum when perpendicular to magnetic field

Practice Problems:

  • 2025 FRQ Question 4

Unit 6: Electromagnetic Induction

Induction can probably be learned in a few days–only the basics are necessary to know for the actual test. Spend more time on magnetic flux though; it’s often an FRQ question by itself. 

Topic of Importance: Magnetic Flux

  • Bar moving on rails
  • Relationship with induced current & resistance

Study Help:

Tips:
  • Current through a resistor in a bar on rails system: I = dΦ/dt
  • Potential difference over an ideal inductor = 0
    • Potential difference over a nonideal inductor = nonzero
  • When a switch is first closed, an inductor acts as a current-carrying wire
  • A circuit with only an inductor & capacitor has a sinusoidal current relationship

Practice Problems:

  • 2021 FRQ Sets 1 & 2 Question 3
  • 2022 FRQ Sets 1 & 2 Question 3
  • 2023 FRQ Sets 1 & 2 Question 2
  • 2024 FRQ Sets 1 & 2 Question 3
  • 2025 FRQ Question 2

AP Test Cram/Review Videos

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