#AP Physics 2: Ultimate Study Guide 🚀

Hey there, future physicist! Let's get you prepped and confident for the AP Physics 2 exam. This guide is designed to be your go-to resource, especially the night before the test. We'll break down the key concepts, highlight important connections, and give you the tools you need to succeed. Let's do this!

#1. Electrostatics

#1.1 Conservation of Electric Charge

• Fundamental Principle: The net charge of an isolated system is always conserved.

• Charge Transfer: When objects touch, charge is redistributed until they reach equilibrium.

• Net Charge: The total charge before and after any interaction remains the same.

  

  Caption: When two charged spheres touch, charge is transferred until they reach the same charge.

#CollegeBoard Essential Knowledge:

• Charging by Conduction: Direct contact leads to charge sharing, conserving total system charge.
• Induction: A charged object can cause charge separation in a neutral object nearby.
• Grounding: Excess charge is transferred to/from a large reservoir (like the Earth) 🌎.

#1.2 Conductors and Insulators

• Conductors: Materials with free electrons (e.g., metals like copper, silver, gold). These allow charge to flow easily.

• Insulators: Materials with tightly bound electrons (e.g., rubber, plastic, glass). These resist charge flow.

  

  Caption: Insulators (like rubber) prevent charge from moving, while conductors (like copper) allow charge to flow.

• Electrical Resistance: Conductors have low resistance; insulators have high resistance.

• Electron Mobility: Electrons move easily in conductors, not so much in insulators.

#Example Questions:

Example 1: A copper wire has a length of 1 meter and a cross-sectional area of 0.1 square millimeters. The wire has a resistance of 1 ohm. What is the resistivity of the wire?

Solution:

Using the formula $\rho = \frac{RA}{L}$, we get $\rho = \frac{(1 \Omega)(0.1 \times 10^{-6} m^2)}{1 m} = 1 \times 10^{-7} \Omega \cdot m$. Note that you need to convert $mm^2$ to $m^2$.

Example 2: A copper wire has a length of 2 meters and a cross-sectional area of 0.2 square millimeters. The wire has a resistivity of 1 \times 10^{-7} \Omega \cdot m. What is the resistance of the wire?

Solution:

Using the formula $R = \frac{\rho L}{A}$, we get $R = \frac{(1 \times 10^{-7} \Omega \cdot m)(2 m)}{0.2 \times 10^{-6} m^2} = 1 \Omega$.

Example 3: What is a device called that transfers electric charge? What are its main characteristics?

Solution:

It's called an electric conductor. Main characteristics include low resistance, high electron mobility, and good conductivity.

#2. Electric Fields and Forces

#2.1 Coulomb's Law

• Force Equation: $F = k \frac{|q_1 q_2|}{r^2}$, where:
  • $F$ is the electrostatic force
  • $k$ is Coulomb's constant (8.99 \times 10^9 N m^2/C^2) ...