test 1 summary 222
test 1 summary 222 Phys 222
U of L
Popular in Fundamentals of Physics II
Popular in Physics
This 6 page Study Guide was uploaded by Mary-elizabeth Notetaker on Saturday September 24, 2016. The Study Guide belongs to Phys 222 at University of Louisville taught by Dr. Ming Yu in Fall 2016. Since its upload, it has received 43 views. For similar materials see Fundamentals of Physics II in Physics at University of Louisville.
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Date Created: 09/24/16
e is unit charge... 1.6 X 10 C conductors- electrons move freely in response to electric force and charge distributes evenly ex)copper, aluminum, silver "charging by conduction"- object being charged is always left w same charge as object that did charging induction(no contact) if neg rod touched uncharged sphere, electrons redistribute in sphere if grounded wire is connected, some electrons will leave thru wire if it is removed, sphere will be left w positive charge that will redistribute if rod is then removed, insulators - electrons don't move freely to charge Coulomb's law- electric force has following properties: o Directed along line joining 2 charged particles o Inversely proportional to square of separation distance (r) btwn them Proportional to product of mags of charges q1 and q2 on the particles Electrostatic forces- electric forces btwn 2 unmoving charges Magnetic forces- moving charges Field force- force exerted by one object on another object even tho there is no physical contact btwn them Electrical v gravitational force Stronger weaker Attractive or repulsive always attractive Both: directed along line btwn 2 particles inverse square laws math form: masses(m1, m2) replaced by charges (q1,q2) G replaced by k Superposition principle: o Number of separate charges act on charge of interest(q1) Each charge exerts electric force on q1 Resultant force on any one charge equals vector sum of forces exerted by other indiv charges present Find electrical forces btwn pairs of charges separately, then add vectors Must find both portions and add each then add together Electric current- movement of charged particles " field(E)- EM field- whole space centered at charged object o Direction of field is dir of electric force that would be exerted on small pos test charge placed at that point.. Test charge must not cause rearrangement of source charge o Electric field produced by neg charge(Q<0) is directed toward the charge, so positive test charge would attract… if from pos charge(Q>0) test charge would repel o Electric field from 2 point charges: Find x and y components Sum x and y components Use pythagorean to find mag of resultant field Use inverse tan to find dir of resultant field " potential- capacity for EM to do work on electrical charge If source charge pos, lines radiate outward radically in all dir o If neg, radial lines point inward to infinity o If group of charges, lines start at pos and end at neg o if excess of charge, some lines will begin/end infinitely far away o Number lines drawn leaving pos/ending neg is always same and proportional to mag of charge 2 like charges, lines start at pos and end at infinity…electric field line is tangent to those lines o Bulging out around charges indicated repulsion o Low field lines btwn charges shows weak field in that region o If 2+ with -, only half the lines that leave pos charge will end at neg charge…. 2x number lines leaving +2 as ending on – Field just outside conductor is perpendicular to conductor's surface Field accumulates on smallest(sharpest) points so stronger Electric flux: Gauss’s Law Mag of EF everywhere on surface: E flux thru any closed surface is equal to net charge Q inside surface divided by E Flux thru ends is EA , no field thru curved part of surface\ Find field above/below sheet with uniform negative charge per unit area (cylindrical) Same as above: sum top bottom and side. But E will be negative in bottom equation bc field is pointing towards sheet Parallel Plate Capacitor- plates of neg and pos charge w same charge density For pos plate, E field points away from plate at all positions For neg plate, E field points towards plate at all positions Total E field is sum of E+ and E- at all positions Wab=Fconservative x d= -(Peb-Pea)= - PE Work done by conserv force= -change of PE Conserv force PE Where PE: electric PE diff(final-intial) Electric PE- scalar Change od electric PE is independent of path, depends on distance PE(path1)= PE(path2) To obtain electric PE diff: E potential diff( V) btwn 2 points= change in PE of a charge q moved from A to B divided by size of the charge EP and charge mvmts o When released from rest, pos charges accelerate spontaneously along field direction Pos charge moves along the field direction…EF does positive work o When released from rest, negative charges accelerate spontaneously opp to field direction Negative charge moves opp to field dir… E field does pos work When at rest neg charge goes to dir of lower EP, work must be done by external force against EF Point of 0 EP is taken to be infinite distance from the charge EP of multiple point charges 1. Diagram all charges(note point of interest) 2. Calc distance from each charge to point of interest 3. Use: V=ke(q/r) a. Include sign b. If potential is pos, charge is pos…same w neg 4. Get algebraic sum If charges have same sign, PE is positive Pos external work must be done to force 2 charges near one another If charges have opp signs, PE is neg Ex work must be done to hold back unlike charges from accelerating as they are brought close together Eqiupotential surfaces- surface on which all points are at same potential V=Vb-Va=0 Wab= - PE=-q V=0 No work needed to move chrge at constant speed on equipot surface Electric field is perpendicular to equipot surface Equipot & EF lines Potential dec along direction of EF lines …dipole If has one pos and one neg,point closer to positive charge has higher potential and it decreases along EF line as you go towards the negative charge …parallel plates If one pos and one neg, points closer to pos have higher potential Electric field does 0 work along path perpendicular to plates Capacitance- quantity characterizing 2 parallel plates conductor and is indep of Q and V Capacitor- used in variety of electrical circuits Capacitance, C, of capacitor is defined as ratio of mag of the charge on either conductor(plate) to the mag of the pot diff btwn the 2 plates Larger area can store more charge so enhances capacitance Small plate separation can dec pot diff and will enhance capacitance Flow stops when V across capacitor = that of battery Capacitors in serier As neg charge accumulates on plates of one group, equivalent amt neg charge is leaving plates of the other group(left w excess pos charge) ..mag of charge must be same on left plate(outer) of C1(group left w pos charge) and right plate(outer) of C2(group accumulating neg charge) For charges on inside plates…: Internal plates connected to each other but not battery so they are electrically neutral. Charges are induced by outside plates in series …Overall, all right plates gain -Q charge and all left plates gain +Q charge Equivalent capacitor can be found that performs same fx as series combo does Battery- transfers charges from one plate to another when connected Stored E is same as work req'd to move charge onto plates done by battery Total work by battery & energy stored Max capacitance, 3 capacitors must be parallel Max pot diff, 2 batteries must be in a series Dielectric- insulating material that inc capacitance when placed btwn 2 plates of a capacitor Rubber, plastic, wax paper Capacitance mult by k(dielectric constant) when dielectric completely fills region btwn 2 plates Polarization- occurs when separation btwn avg positions of neg and pos charge Current direction is along dir pos charges would flow =conventional current dir In common conductor, current is due to net motion of neg charged e-'s Charge carrier- moving charge(+ or -)
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