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PS 250: Lecture 1 Course Introduction and Electric Charge

J. B. Snively August 24, 2015

Today’s Class

Friendly Introductions! Syllabus and Course Format Introduction to Electric Charge Summary

Part 1: Electrostatics

Chapter 21: Electric charge and the electric field

Chapter 22: Gauss’s Law

Chapter 23: Electric Potential

First exam covers basics of electrostatics!

Part 2: Capacitors, Circuits, Current...

Chapter 24: Capacitance and Dielectrics

Chapter 25: Current, Resistance, Electromotive Force

Chapter 26: Direct-current (DC) Circuits

Chapter 27: Magnetic Fields and Forces

Second exam covers basics of electric current, circuits, and magnetic forces!

Part 3: Magnetic fields, induction, inductance...Chapter 28: Sources of Magnetic Fields

Chapter 29: Electromagnetic Induction

Chapter 30: Inductance

Third exam covers basics of magnetic fields and electro-magnetics, including the coupling between electric and magnetic fields.

Part 4: Electromagnetic Waves, Modern Physics...

Chapter 32: Electromagnetic Waves

Chapter 37: Special Relativity

Chapter 38: Basics of Atomic Physics

Comprehensive final exam covers ALL topics previously discussed, plus basics of electromagnetic waves (light / radio) and modern physics!

Today’s Class

Friendly Introductions! Syllabus and Course Format Introduction to Electric Charge Summary

What is Charge?Characterized as Negative or positive

Fundamental property of matter which is:

Conserved (due to transfer of persistent individual charge carriers, typically electrons)

Quantized (due to discrete nature of electrons and other charged particles)

“Electrostatics”: Behavior of charges that are at rest (i.e, static).

Conservation and Quantization of ChargeCharge cannot be created or destroyed. Therefore: Charge is (Universally) Conserved: “The algebraic sum of all the electric charges in any closed system is constant.”

Charge is defined by individual subatomic particles (electrons/protons). Therefore: Charge is Quantized: “The magnitude of charge of the electron or proton is a natural unit of charge.”

Structure of an Atom

Neutral atoms may gain/lose electrons, resulting in “Ions”

Positive Ion: Fewer electrons than protons

Negative Ion: More electrons than protons

“Ionization” is the process of gaining / losing electrons.

Charging by Friction

-+

“Opposite” Charges Attract:

--

“Like” Charges Repel:

++

Glass tends to lose electrons, plastic tends to hold on to electrons

Total charge remains constant – Shared between ball, rod,

and the conductive wire.

Charging by Conduction

Charging by Induction

The negatively charged rod induces an accumulation of negative charge on opposite

side of the metal ball.

Polarization

Even uncharged insulators are weakly affected by the presence of external charges.

Material PropertiesInsulators (Dielectrics): Typically non-metals, which do not allow free motion of charge – Charge accumulates on and within.

Conductors: Typically metals, which allow free transfer of charge. Electrons move freely, and charge accumulates on surface.

Semiconductors: Intermediate materials which allow charge to move under certain conditions – Basis for “nonlinear” circuit elements (diodes, transistors).

Summary / Next Class:

Read Textbook Sections: 21.1–21.4

Figure out how to access Mastering Physics Course “PS250SNIVELYFA15”

Visit website! The online syllabus/schedule is always the preferred version.

Prepare to discuss!