PHYSICS 272 Electric & Magnetic Interactions Prof. Yulia Pushkar ypushkar@purdue.edu Room: 70, Phone: 63279

Course Content This course deals with electric and magnetic interactions, which are central to the structure of matter, to chemical and biological phenomena, and to the design and operation of most modern technology. The main goal of this course is to have you engage in a process central to science: the attempt to model a broad range of physical phenomena using a small set of powerful fundamental principles. The specific focus of the course is an introduction to field theory, in terms of the classical theory of electricity and magnetism (E&M). The course also emphasizes the atomic structure of matter, especially the role of electrons and protons in matter.

Textbook The textbook is Matter & Interactions, vol II: Electric & Magnetic Interactions by R. Chabay & B. Sherwood (John Wiley & Sons 2007). We will cover almost all of the topics in this volume. Make sure it is the Third Edition. The new book comes with a free coupon for WebAssign, the on-line homework service. Follow the instructions and get yourself registered.

General Information Room PHYS 144: Undergraduate office Room PHYS 12: Help center Room PHYS 290: Physics Library We will use WebAssign for homework and lab assignments. You will be able to access your scores in CHIP. See “Important Links” on course web page for details! For questions concerning WebAssign contact: V.K. Saxena: Office: PHYS 176, Phone: 49575

Activities and Responsibilities In-class activities and responsibilities You are responsible for attending all classes, and attendance will count toward your grade. Bring a scientific calculator to class. If you miss class, it is your responsibility to find out what you missed. Lectures slides will be available shortly after lecture concludes. Homework Homework and lab assignments will be posted on the web. See WebAssign (and Calendar section) for due dates. Outside class Study assigned textbook sections. An assignment to study sections of the textbook means: Read the assigned textbook sections thoughtfully. Do the "stop and think" activities. Write brief solutions to the in-line "exercises" and keep them in a notebook.

Quizzes, Exams, Grades Clicker Questions in Lecture: Exams: Grades: Short multiple choice questions will be posed in lecture. The purpose is to assess your understanding. It will also be used to check attendance. We will start counting clicker questions towards your grade at lecture #4. You have to purchase an iClicker ( http://www.iclicker.com ) from the bookstore. You must register your clicker ID in CHIP!!!! Exams: There will be two 1.5-hour exams and a 2-hour final exam. All exams are closed-book, but relevant formulas and constants will be provided. Grades: The final grade will be determined on the following basis (Course Total = 700 points): 200 points - final exam 100 points each - two 1.5-hour exams (8-9:30 pm Feb 18, March 31) 75 points - WebAssign homework 100 points – Labs 25 points - Clicker Questions & Attendance 100 points – Recitation Problems

Argonne National Laboratory

Synchrotron

Clicker Question 1 Set your clicker frequency to AB My major is – Engineering Science Liberal Arts Education Other

The origin of word “electron” comes from Set your clicker frequency to AB Clicker Question 2 Set your clicker frequency to AB The origin of word “electron” comes from current caring wire fossilized tree resin spring flower attraction between objects The ancient Greeks noticed that amber attracted small objects when rubbed with fur. Along with lightning, this phenomenon is one of humanity's earliest recorded experiences with electricity. [15] In his 1600 treatise De Magnete, the English scientist William Gilbert coined the New Latin term electricus, to refer to this property of attracting small objects after being rubbed. [16] Both electric and electricity are derived from the Latin ēlectrum(also the root of the alloy of the same name), which came from the Greek word for amber, ἤλεκτρον (ēlektron).

The word electron was coined in 1894 by Johnstone Stoney (an Irish physicist) and is derived from the Latin electrum or the Greek elektron meaning amber (fossilized tree resin). Electrostatic charge can be generated by rubbing amber with wool and it is done for demonstrating the electrostatic charge phenomena to elementary students.

Structure of Atom Matter consists of atoms 1 cm3 : ~1024 atoms . Nucleus Proton is positively charged neutron 0 mp mn  1.7*10-27 kg 10-14m electron is negatively charged Electron cloud size is about 10-10m = 1Å The word electron was coined in 1894 by Johnstone Stoney (an Irish physicist) and is derived from the Latin electrum or the Greek elektron meaning amber (fossilized tree resin).

Point Charges Two types: positive and negative Like charges: repel Opposite charges: attract Charge is quantized in units of e Millikan’s oil drop experiment (1910-1913) Point charge: Size is small compared to the distance between it and other objects of interest Electric charge is an intrinsic property of the fundamental particles that everything is made of Positive/negative – just definition, can call red-green. Electron/protons – often are treated as point charges. Proton=1e-15 m.

Charles-Augustin de Coulomb The Coulomb Force Law Charles-Augustin de Coulomb (1736 - 1806) "The magnitude of the electrostatic force between two point charges is directly proportional to the magnitudes of each charge and inversely proportional to the square of the distance between the charges." Q1 Q2 F Charles Augustin de Coulomb – French engineer and scientist. Created science of friction (first), after that stopped engineering and became involved full time in physics, in 1785-1791 published 7 papers on electricity and magnetism: ... had obtained some remarkable results by using the torsion balance method: law of attraction and repulsion, the electric point charges, magnetic poles, distribution of electricity on the surface of charged bodies and others. The importance of Coulomb's law for the development of electromagnetism is examined and discussed. In these he developed a theory of attraction and repulsion between bodies of the same and opposite electrical charge. He demonstrated an inverse square law for such forces and went on to examine perfect conductors and dielectrics. He suggested that there was no perfect dielectric, proposing that every substance has a limit above which it will conduct electricity. These fundamental papers put forward the case for action at a distance between electrical charges in a similar way as Newton's theory of gravitation was based on action at a distance between masses.

The Coulomb Force Law 0 = permittivity constant Force repulsive + 1 + 2 r F21 Force attractive + - 2 r F21 1 Force on “2” by “1” The force exerted by one point charge on another acts along line joining the charges. The force is repulsive if the charges have the same sign and attractive if the charges have opposite signs.

Units and Constants SI units of electric charge: Coulomb, C Constants: 1/40 = 9x109 N.m2/C2 0 = 8.85x10-12 C2/N.m2 permittivity constant e = 1.602x10-19 C 1 C = 6.24x1018 elementary charges Particle Charge electron -e positron +e proton +e antiproton -e muon +e or –e pion +e or –e or 0 neutron 0

How Strong is the Coulomb Force

Definition of Electric Field

Electric Field If our probe charge is positive or negative – F due to given E will point in correct direction. [N/C] Electric field has units of Newtons per Coulomb:

The Electric Field of a Point Charge + - Direction and magnitude

Electric Field There is something in space waiting for a charged particle to interact with it! This virtual force is called electric field. An electric field created by charge is present throughout space at all times, whether or not there is another charge around to feel its effect.

The Physical Concept of ‘Field’ Field: physical quantity, can be scalar or vector Examples: Temperature T(x,y,z,t) Air flow, gravitational field m q

Example Problem Solution: A particle with charge +2 nC (1 nanoCoulomb=10-9 C) is located at the origin. What is the electric field due to this particle at a location <-0.2,-0.2,-0.2> m? Solution: Distance and direction: Note: r – direction is from source to point of observation.

Example Problem 2. The magnitude of the electric field: 3. The electric field in vector form:

Forces due to an Electric Field Example: The electric field at a particular location is <-300,0,0> N/C. What force would an electron experience if it were placed in this location? Y E e F X Solution:

No ‘self-force’! Point charge does not exert field on itself! Physically makes sense – it cannot start itself moving, there is no way to decide in which way to move.

The Superposition Principle The net electric field at a location in space is a vector sum of the individual electric fields contributed by all charged particles located elsewhere. The electric field contributed by a charged particle is unaffected by the presence of other charged particles.

The Superposition Principle