#AP Physics C: E&M - Ultimate Study Guide ⚡

Hey there, future physicist! Let's get you prepped and confident for the AP Physics C: E&M exam. This guide is designed to be your go-to resource, especially the night before the test. Let's dive in!

#1. Fundamental Concepts of Electric Charge

# Charge as a Scalar Quantity 🔋

• Charge is a fundamental property of matter, measured in coulombs (C).
• It's a scalar, meaning it has magnitude but no direction.
• Charges can be positive (+) or negative (-).
• The smallest unit of charge is the elementary charge (e), which is the magnitude of charge on a single electron or proton.
  • Electron: -e
  • Proton: +e
  • Neutron: 0 (neutral)

# Coulomb's Law ⚖️

• Describes the electrostatic force between two point charges.

• The force is:

  • Directly proportional to the product of the magnitudes of the charges.
  • Inversely proportional to the square of the distance between them.

• Formula:

  $$|\vec{F}_E| = k \frac{|q_1 q_2|}{r^2}$$

  • $|\vec{F}_E|$ = magnitude of the electrostatic force
  • $q_1$, $q_2$ = magnitudes of the charges
  • $r$ = distance between the charges
  • $k$ = Coulomb's constant ($k = \frac{1}{4 \pi \varepsilon_0} \approx 8.99 \times 10^9 N m^2/C^2$)
  • $\varepsilon_0$ = permittivity of free space

#Direction of Electrostatic Force

• Force acts along the line connecting the two charges.
• Like charges (++, --) repel each other.
• Opposite charges (+-) attract each other.

#Macroscopic Properties

• Electric forces are fundamental, but on a macroscopic level, we often use non-fundamental contact forces (normal, friction, tension) because of the vast number of particle interactions.