Gabriela González. Physics 2102 Gabriela González. Office hours: Nicholson 271-C, Tue 5:30-6:30pm, Th 5-6pm or by appt.

Transcription

1 Physics 2102 Gabriela González Charles-Augustin e Coulomb ( ) Office hours: Nicholson 271-C, Tue 5:30-6:30pm, Th 5-6pm or by appt Phone: gonzalez@lsu.eu Research: Detection of Gravitational Waves ligo.org einsteinmessengers.org Gabriela González 1

2 2102 Class website: Our Section website: Scheule, graing policy, syllabus all poste here. Check both often!! Lectures will be poste in our section s website. Textbook: Funamentals of Physics, Halliay, Resnick, an Walker, 9th eition. We will cover chapters in this class. You have access to the online textbook in WileyPlus.com Exams: Two miterms: 6-7pm, Thursays Feb 24 an Mar 31. Final Exam (cumulative): We May 11, 3-5pm Web-base system: WileyPlus.com To register, go to Notice that this is only for section 5! me (gonzalez@lsu.eu) ASAP if you have any trouble. There will be one assignment per week, ue We 2am (Tue late night) The first assignment is ue We Jan 26, on Ch 21. 2

3 Score Feb 24 exam (100 pts) Mar 31 exam (100 pts) Final Exam (150 points) Homework (25 points) Course grae is guarantee to be at least as follows: Electric charge Electric force on other electric charges Electric fiel, an electric potential Moving electric charges : current Electronic circuit components: batteries, resistors, capacitors Electric currents Magnetic fiel Magnetic force on moving charges Time-varying magnetic fiel Electric Fiel More circuit components: inuctors All together: Maxwell s equations Electromagnetic waves Optical images Matter waves 3

4 Two types of charges: positive/negative Like charges repel Opposite charges attract Charles-Augustin e Coulomb ( ) or or Coulomb s law -- the force between point charges: Lies along the line connecting the charges. Is proportional to the magnitue of each charge. Is inversely proportional to the istance square. Note that Newton s thir law says F 12 = F 21!! 4

5 For charges in a VACUUM k = Often, we write k as: Question: How o we figure out the force on a point charge ue to many other point charges? Answer: consier one pair at a time, calculate the force (a vector!) in each case using Coulomb s Law an finally a all the vectors! ( superposition ) Useful to look out for SYMMETRY to simplify calculations! 5

6 q 1 = q 2 = q 3 = 20 µc Three equal charges form an equilateral triangle of sie 1.5 m as shown Compute the force on q 1 What is the force on the other charges? q 2 q 1 q 3 y Solution: Set up a coorinate system, compute vector sum of F 12 an F α 3 x +q Charge +q place at center What is the force on central particle? 6

7 Total amount of charge in an isolate system is fixe ( conserve ) Example: 2 ientical metal spheres have charges +1C an 2C. You connect these together with a metal wire; what is the final charge istribution? +1C 2C?? Charge is always foun in INTEGER multiples of the charge on an electron/proton ([[why?]]) Electron charge = e = 1.6 x Coulombs Proton charge = p = +1.6 x Coulombs Unit of charge: Coulomb (C) in MKS units One cannot ISOLATE FRACTIONAL CHARGE (e.g. 0.8 x C, +1.9 x C, etc.) [[but what about quarks?]] 7

8 negative electron clou nucleus of positive protons, uncharge neutrons Z = atomic number = # of protons = # of electrons in a neutral atom A = mass number = # of protons (Z) + # of neutrons (N) electron charge = e = 1.6 x Coulombs = - proton charge electron mass = kilograms proton mass = kilograms = neutron mass In a conuctor, electrons move aroun freely, forming a sea of electrons. This is why metals conuct electricity. Charges can be inuce (move aroun) in conuctors. Blue backgroun = mobile electrons Re circles = static positive charge (nuclei)

9 In an insulator, each electron clou is tightly boun to the protons in a nucleus. Woo, glass, rubber. Note that the electrons are not free to move throughout the lattice, but the electron clou can istort locally. + - An object can be given some excess charge: giving electrons to it (we give it negative charge) or taking electrons away (we give it positive charge). How o we o charge an object? Usually, moving charges from one surface to another by ahesion (helpe by friction), or by contact with other charge objects. If a conuctor, the whole electron sea reistributes itself. If an insulator, the electrons stay where they are put. 9

10 Electric charges come with two signs: positive an negative. Like charges repel, opposite charges attract, with a magnitue calculate from Coulomb s law: F=kq 1 q 2 /r 2 Atoms have a positive nucleus an a negative clou. Electron clous can combine an flow freely in conuctors; are stuck to the nucleus in insulators. We can charge objects by transferring charge, or by inuction. Electrical charge is conserve, an quantize. 10