Electricity and Magnetism PHY211 Overview

Study Notes

Lecture Layout:
- Electric charges
- Conductors and Insulators
- Charging
- Activity
Electric Charge:
- Measurable quantity of matter, with symbols q or Q, units are in Coulombs (C).
- Quantized; comes in units of e = 1.6 x 10^-19 C
- Elementary particles within atoms
  - Protons: +e = +1.6 x 10^-19 C
  - Neutrons: Uncharged
  - Electrons: -e = -1.6x 10^-19 C
- Neutral bodies: equal amounts of positive and negative charges
- Charged bodies: unequal amounts, more of one type
- Like charges repel, unlike charges attract
Charging by Friction
- Rubbing transfers electrons between objects
- Example: Glass rod-silk, plastic rod-fur

Electrical Conductors: Materials with free electrons (electrons can move freely).
- When charged, charge distributes across the entire surface
- Example: Copper
Electrical Insulators: Materials where all electrons are tightly bound to atoms (electrons cannot move freely).
- Charge stays localized when charged
- Example: Plastic
Semi-conductors: Materials with electrical properties between conductors and insulators.
- Resistivity increases with decreasing temperature
- Affected by impurities and junctions and has variable resistance, sensitive to heat and light (current flows more easily in one direction).
- Example: Silicon, Germanium

Charging by Conduction: Sharing charge by direct contact between charged and neutral objects.
Charging by Induction: Charged object influences another object without contact. This creates a charge separation but doesnt necessarily transfer any charge. Often this involves a grounded conductor

A charged rod attracts bits of dry cork dust that jump away after touching.
A charged insulator can be discharged by passing it near a flame (heat dislodges electrons).
Why a coin rubbed between fingers doesn't become charged.