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Physics 114 Professor Fred Salsbury Office Hours: Tuesday 4-5 pm and Thursday 2:30-3:30 pm, or by appointment in 301A Olin Tutorials : TBA http://www.wfu.edu/~salsbufr http://www.webassign.net [email protected] Topics Covered •Electricity and Magnetism •Nuclear Physics Please Pick Up and READ the Course Policies, Syllabus and Voting Cards Class Participation •Bring your voting cards to every class period •If you forget them, borrow some from me •If you lose them, get new ones from me I will give extra credit points for productive class participation. Do you understand how the voting system works? A) Yes, I’ve done it before B) Yes, though it is new to me C) Sort of, I’ll figure it out D) No, I am totally confused Assignments Reading Assignments: on Webassign Every lecture Reading quizzes, due 7am before lecture STARTING THURSDAY Covering reading and review: typically 3-5 MC/essays ~5 submissions: Work by yourself Homework: on Webassign Due every T/Th 10pm; STARTING TUESDAY Will include review of vectors and calculus Typically 4-5 problems ~10 submissions: Encouraged to work with others Quizzes and Final Quantitative questions, qualitative questions and derivations. If you miss any quiz/exam, I need a note from a medical doctor or the Dean’s office. Lowest Semester quiz is work ½ credit Webassign http://www.webassign.net/student.html •Username is your email (without @wfu.edu) •Institution is wfu •Password (if new to webassign) is your student number •Without leading zeros •If you have used webassign before use your old password. There is a test homework on using webassign. Log into webassign ASAP. Do the Survey and webassign HW If you have difficulty, contact me. Grading Final Exam 330 points Best 3 Semester Quizzes 300 points Homework and Reading Quizzes 300 points Worst Semester Quiz 50 points Laboratory 20 points You must pass lab to pass the course. You are expected to pass the final to pass the class. Productive class participation will earn extra points. This course is not “curved”. This course is not graded on a 10 point scale. Each assignment will have cutoffs and the cutoffs are averaged. If the course is significantly off track, then the last quiz will be cancelled. Content This class has a substantial mathematical component, and is calculus-based. 11.5 lectures on electricity Ch. 22-28 1.5 lectures on nuclear physics Ch. 43 8.5 on magnetism and electromagnetic waves Ch 29-34 If time permits, additional topics in optics Some additional topics {e.g. geometric optics and additional electronics} will be covered in lab Web Information How to access course info: •Go to www.wfu.edu/~salsbufr •Click on teaching, then on Phy114A2005 •There will be a page for general announcements, and a sidebar Lectures notes will be posted on the web page, as are the syllabus and course policies. If you have trouble using it, contact me! Coordinate systems Different ways of representing space, and physics. Some problems are easier in some coordinate systems, but the physics is invariant. Cartesian Coordinates: Polar Coordinates Another popular coordinate system along with cylindrical and spherical x r cos y r sin y tan x r x y 2 2 Vectors and Scalars Vectors: Magnitude and direction Scalars: Magnitude Displacement is a vector. Velocity is a vector. Acceleration is a vector. Vector Components: Geometric The x- and y-components of a vector: Ax A cos Ay A sin The magnitude of a vector: A Ax Ay 2 2 The angle between vector and x-axis: Ay tan Ax 1 Vector Components: Algebraic • • • • A unit vector is a dimensionless vector having a magnitude 1. Unit vectors are used to indicate a direction. i, j, k represent unit vectors along the x-, y- and z- direction . x̂, ŷ, ẑ is another common notation. • i, j, k form a right-handed coordinate system. A = Axi + Ayj Vector Addition: Algebraic I We want to calculate: R=A+B From diagram: R = (Axi + Ayj) + (Bxi + Byj) R = (Ax + Bx)i + (Ay + By)j The components of R: Rx = Ax + Bx Ry = Ay + By Vector Addition: Algebraic II The magnitude of R: R Rx Ry ( Ax Bx ) 2 ( Ay By ) 2 2 2 The angle between vector R and x-axis: Ry tan Rx Ay By Ax Bx Vector Multiplication There are two ways (in 2 or 3D) to multiply vectors. Scalar product -> two vectors make a scalar A B N Also called the dot product or the inner product Vector product -> two vectors make a vector A B C Also called the cross product or the outer product Scalar Product Scalar product -> two vectors make a scalar A B ab cos Geometric A B axbx a y by az bz Algebraic Vector Product Vector product -> two vectors make a vector A B C Geometric C has magnitude absin. Direction perpendicular to the plane containing A and B. Algebraic A B (a y bz by az )i (az bx bz ax ) j (axby bx a y )k The right hand rule Force F velocity v Magnetic Field B F q vB F qvB sin Electricity and Magnetism •One of the four fundamental forces of nature •Responsible for the vast majority of what we observe around us •Probably best-understood and best-tested of the forces of nature Electromagnetic Interactions: •Electricity and Electronics •Magnetism •Chemistry •Biology • and even more Electrical Charges •Electric forces only affect objects with charge •Charge is measured in Coulombs (C). A Coulomb is a lot of charge! •Charge comes in both positive and negative quantities •Charge is conserved – it can neither be created nor destroyed •Charge is usually denoted by the letter q. An object has a total charge of 5 mC. It is divided into two pieces, one of which has charge 8 mC and the other of which has charge A) 3 mC B) -3 mC C) 13 mC D) Such a division is impossible Charge Densities Charge can be localized to discrete points (point charges), or it may be spread out over a volume, a surface or a line •Charge density units C/m3 •Surface charge density units C/m2 •Linear charge density units C/m A cube with side 1 cm has a charge density of = 1 C/m3. What is the charge of the cube? A) 1 C B) 0.01 C = 10 mC C) 10-4 C = 100 m C 1 cm D) 10-6C = 1 mC Some ways to charge objects •By rubbing dissimilar objects •By chemical processes •By proximity between a charge and a conductor – charging by induction •By physical contact between a charge and a conductor + - +
