Physics 2220 Electromagnetism, Basic Circuits, Optics

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1 Physics 2220 Electromagnetism, Basic Circuits, Optics Dr. Andrew Smith Lecture #1

2 Who am I? Milky Way Galactic Center B.A. Astrophysics: UC Berkeley 2001 M.Sc. Elementary Particle Physics: University of Durham (UK) 2002 Ph.D. High Energy Astrophysics: University of Leeds (UK) 2007 Lecturer: Northwestern University ( ), Current: Research Assistant Professor (UU) Gamma-ray Astrophysics (VERITAS): supernovae, pulsars, black holes, dark matter...

3 Who are you? Mostly engineers, some chemistry, some geoscience, some other things... Some returning students, some just out of high school... For some this may be one of the more difficult courses you take...

Administrative: Course Website: www.physics.utah.

4 Administrative: Course Website: Physics2220/ My Office Hours: MWF, 4-5 SP 223 TAs: Michael Newbold (Marshall) Lauren Richey Matthew Groesbeck Chad Miller

5 This course is taught as a classical lecture course, but makes use of more modern tools: We will use the SmartPhysics system for HW and checkpoints ( Course Code: 2220_Fall_2013 Enroll in SP this week: You have a checkpoint due this Friday! SmartPhysics consists of 3 parts: -PreLectures (Optional) -Checkpoints (Mandatory) -Homework (Mandatory)

6 Prelectures: Not Required, but highly recommended... Checkpoints: Do After Lecture! They help me to prepare and review most effectively for you HW: Due 11:59pm day indicated (70% credit 24 hours later)

7 Your Grade: 105 points Checkpoints: 10 points Homework: 25 points 3 Midterms: 45 points Final Exam: 25 points HW: 26 Assignments over semester, each 1 point, I drop lowest oneno makeups Midterms: No early or makeup exams, I drop lowest MT if your final exam score is higher than avg of 3 MTs I will curve grades at the end of the semester- usually the mean equates to a C+/B-

8 Doing Well in This Class... Take advantage of my office hours Go to discussion section Help Lab if you are having problems (or feeling confident- Go help others!) Ask questions! Don t be afraid to appear confused- chances are you aren t alone. STUDY STUDY STUDY

9 What will we learn? Electrostatics (stationary electric charges) and time constant electric fields Magnetism + time varying electric fields Basic DC, RC, AC circuitry Electromagnetic waves + Maxwell s Equations Basic Optics Some Special Relativity

10 How will we learn? Small->Large, simple -> complicated Take simple concepts in simple situations-> then make these situations more complicated. Appeal to conceptual power of things like symmetry, conservation laws. Understand the physics first! The solutions to the problems come later...

11 Why do we study physics?

12 Our power to understand Nature is dependent upon developing specialized languages... Physics is a very profound example of this. Through physics we are able to understand: -the structure of matter and the nature mass -the structure of space and time -the beginning and the end of the Universe

13 Electromagnetism? Physics is the study of energy and fields. Up until now you have studied the behavior of objects in gravitational fields (kinetic, potential energy) This class will (more or less) be about learning the language of the behavior of objects under the influence of other types of fields (electric + magnetic). Learning to think in this way will benefit your studies elsewhere (its true!)

14 Why should we care about EM? 1.)Academic practicality A study of E&M (+quantum) forms the conceptual base for almost all advanced physics to come after. (okay, well Im not a physicist- so what?)

15 Why should we care about EM? 2.)General Street Smarts

16 Why should we care about EM? 2.)Philosophical Aesthetic Luminous beings are we, not this crude matter - Yoda

18 Key Players Conductors:Atomic structure results in loosely bound electrons which can easily move ->conduction electrons, and remaining positive nuclei->positive ions. Insulators: Materials whose atomic structure dont permit charge to move freely. (Plastics, rubber etc.) Also semiconductors, superconductors (we ll worry about those later...) Ground: Infinite source/sink for electrons

19 Charge? Ancient Greeks knew about charge (kinda)- observed amber rubbed with silk would move dry leaves... 18th Century: 2 types of charge- glass rubbed with silk, and rubber rubbed with fur (A and B).

20 Ben! Ben Franklin observed that A repels A, B repels B, but A attracts B. (Arbitrarily made one negative...) Benjamin Franklin (January 17, 1706 [O.S. January 6, 1705[1]] April 17, 1790) was one of the Founding Fathers of the United States. A noted polymath, Franklin was a leading author and printer, satirist, political theorist, politician, postmaster, scientist, inventor, civic activist, statesman, and diplomat. As a scientist, he was a major figure in the American Enlightenment and the history of physics for his discoveries and theories regarding electricity. He invented the lightning rod, bifocals, the Franklin stove, a carriage odometer, and the glass 'armonica'. He formed both the first public lending library in America and the first fire department in Pennsylvania.

21 Charge? LIKE CHARGES REPEL, OPPOSITE CHARGES ATTRACT CHARGES ARE CONSERVED: Ben Franklin knew this also- impressive! Fundamental unit of Charge: Coulomb (1 electron charge = 1.6e-19 C)

22 In conductors, charges can easily rearrange themselves because they can move freely. What about in non-conductors? Induced charge due to polarization

23 Van de Graff

24 So: We know like charges repel, opposites attractwhat do we mean by attract + repel? Answer: Force exerted

25 Coulomb s Law k

26 Similar to Gravitation Both depend on charge of points Both have inverse square dependence on distance Both are reflexive Both obey principle of superposition

27 Coulombs Law Also obeys Superposition: F3,net = F1,3 + F2,3 + F4,3+ F5, 3...

28 Charges don t really exert force on each other Well, okay they sorta do- BUT there is a much more elegant way of looking at the situation- by asking the question: How do the charges know about each other?

29 Answer: The Electric Field By the nature of their existence, charges create a field around them. Other charges sense this field and react to it. Charges react/interact with this field by experiencing FORCES. The magnitude/direction of this force is determined by the magnitude/ direction of the field->in turn determined by the magnitude/sign of the charge that created the field.

History. The word electricity comes from the Greek elektron which means amber. The amber effect is what we call static electricity.

History. The word electricity comes from the Greek elektron which means amber. The amber effect is what we call static electricity. Electrostatics 1 History The word electricity comes from the Greek elektron which means amber. The amber effect is what we call static electricity. 2 ELECTROSTATICS the study of electric charges, forces