Physics 212 Lecture: Electricity and Electric Charge

This set of flashcards covers critical vocabulary and concepts related to electricity and electric charge discussed in the lecture.

Electric Charge (Q)

A quantized property where Q = ne, with n being an integer and e \approx 1.602 \times 10^{-19} \text{ C} (elementary charge). Measured in Coulombs (C), it is used to determine electromagnetic interactions in atoms and circuits.

Coulomb's Law (F)

Calculates the electrostatic force between two point charges: F = k \frac{|q1 q2|}{r^2}. The constant k = \frac{1}{4\pi\epsilon_0} \approx 8.99 \times 10^9 \text{ N}\cdot\text{m}^2/\text{C}^2. Use case: Determining the net force in a system of stationary charges.

Conductors

Materials with high electron mobility and low resistivity (\rho), such as Copper or Silver (\rho \approx 10^{-8} \, \Omega\cdot\text{m}). Use case: Electrical wiring and electrodes where charge must flow with minimal energy loss.

Insulators (Dielectrics)

Materials with high resistivity (\rho) and tightly bound electrons. Use case: Protective wire coatings and dielectric layers in capacitors to prevent charge flow or store energy.

Electric Field (\vec{E})

A vector quantity representing force per unit charge: \vec{E} = \frac{\vec{F}}{q} or \vec{E} = k \frac{|Q|}{r^2}. Measured in \text{N/C} or \text{V/m}. Use case: Predicting the force on a charge (\vec{F} = q\vec{E}) without needing the source charge details.

Elementary Charges (p^+ and e^-)

Protons have a charge of +1.602 \times 10^{-19} \text{ C} and a mass of 1.673 \times 10^{-27} \text{ kg}. Electrons have a charge of -1.602 \times 10^{-19} \text{ C} and a much smaller mass of 9.11 \times 10^{-31} \text{ kg}.

Electrostatic Force Directions

Force vector direction is determined by charge signs: q1 q2 > 0 results in a repulsive force (+ sign in magnitude), whereas q1 q2 < 0 results in an attractive force (- sign in magnitude).

Charging by Induction

Process of inducing a charge on a conductor by bringing a charged object nearby and grounding the conductor. Use case: Electrostatic precipitators for smoke removal and the operation of an electroscope.

Superposition Principle

For multiple charges, the net force (\vec{F}{net}) or field (\vec{E}{net}) is the vector sum: \vec{E}{total} = \sum{i=1}^{n} \vec{E}_i. Use case: Calculating the electric field produced by complex charge distributions like dipoles or line charges.