ELECTRIC POTENTIALGoings On For the Next Few DaysSlide 3If you got less than 50% on this test (remember that I added 10)What were the issues??So … what next??Slide 7Picture a Region of space Where there is an Electric FieldWhat (or who) must do this work?Electric PotentialI need some help.What we will do ….During this process, who is pushing?When we start the process, the charge that is stationary must be brought up to speed.Start and SopDuring this process, who is actually doing work?ClearlyAbout the work that they do ..Each does the negative amount of work than the other does.So, when we move a charge in an Electric Field ..Summary--And also remember:A nice landscapeThe gravitational case:Someone else’s pathIMPORTANTThe Electric FieldA few things to remember…Electric Potential EnergyDefinition – Potential EnergyExample:Slide 32AN IMPORTANT DEFINITIONUNITS OF POTENTIALLet’s move a charge from one point to another via an external force.Furthermore…ExampleOne Step MoreConsider Two PlatesSlide 40Look at the path issueThe difference in potential between the accelerating plates in the electron gun of a TV picture tube is about 25 000 V. If the distance between these plates is 1.50 cm, what is the magnitude of the uniform electric field in this region?An ion accelerated through a potential difference of 115 V experiences an increase in kinetic energy of 7.37 × 10–17 J. Calculate the charge on the ion.ImportantAn Equipotential Surface is defined as a surface on which the potential is constant.Example: A Set of Equipotenital SurfacesBack To YesteryearField Lines and EquipotentialsComponentsBUTThereforeField Lines are Perpendicular to the Equipotential LinesEquipotentialConsider Two Equipotential Surfaces – Close togetherWhereOver a certain region of space, the electric potential is V = 5x – 3x2y + 2yz2. Find the expressions for the x, y, and z components of the electric field over this region. What is the magnitude of the field at the point P that has coordinates (1, 0, –2) m?Typical SituationKeep in MindUNITSIn Atomic PhysicsCoulomb Stuff: A NEW REFERENCE: INFINITYJust Do It!OK, doing it!For point chargesFor a DISTRIBUTION of charge:Slide 66Slide 67Ponder – What is the potential a distance d from an infinite plane whose charge per unit area is s?Given two 2.00-μC charges, as shown in Figure P25.16, and a positive test charge q = 1.28 × 10–18 C at the origin, (a) what is the net force exerted by the two 2.00-μC charges on the test charge q? (b) What is the electric field at the origin due to the two 2.00-μC charges? (c) What is the electrical potential at the origin due to the two 2.00-μC charges?The three charges in Figure P25.19 are at the vertices of an isosceles triangle. Calculate the electric potential at the midpoint of the base, taking q = 7.00 μC.A disk of radius R has a non-uniform surface charge density σ = Cr, where C is a constant and r is measured from the center of the disk. Find (by direct integration) the potential at P.Example: Find potential at PAn Example finite line of chargeSlide 74Slide 75ContinuingSlide 77ELECTRIC POTENTIALELECTRIC POTENTIALJanuary 5, 2007January 5, 2007Goings On For the Next Few Goings On For the Next Few DaysDaysToday Today –Return Exam #1 Return Exam #1 –Yell at youYell at you–Start PotentialStart Potential–There is a WebAssign PostedThere is a WebAssign PostedWednesday – More of the sameWednesday – More of the sameFriday – Friday – –7:30 AM problem session7:30 AM problem session–Quiz on PotentialQuiz on Potential–Class – Potential + problemsClass – Potential + problemsAverage Grade was 58%If you got less than 50% on this If you got less than 50% on this test (remember that I added test (remember that I added 10)10)You eitherYou either–Didn’t study for this class (probably from Didn’t study for this class (probably from the beginning)the beginning)–You did study and you should ask You did study and you should ask yourself if you really have the skills to yourself if you really have the skills to become an engineer or scientist.become an engineer or scientist.–Yes, I am cruel! But think about it.Yes, I am cruel! But think about it.What were the issues??What were the issues??•You didn’t understand how to use symmetry and avoid integration (#1)•You added vectors as if they were scalars. (#1 and #2)•You didn’t understand the CONCEPT of FLUX.–You were unable to extract and understand information from a graph.So … what next??So … what next??•I will work with you if you want me to …–Utilize office hours for questions•M 7:30-8:15•W 7::30 to 9:15ish•F 8:30-8:15•MOST (not all) MWF 10:30 – 11:30•By appointment–Come to the Friday session and ask questions•F 7:30-8:20Picture a Region ofPicture a Region ofspace Where there is an space Where there is an Electric FieldElectric FieldImagine there is a particle of charge Imagine there is a particle of charge q at some location.q at some location.Imagine that the particle must be Imagine that the particle must be moved to another spot within the moved to another spot within the field.field.WorkWork must be done in order to must be done in order to accomplish this.accomplish this.What (or who) must do this What (or who) must do this work?work?An external An external agent (person)agent (person)The Field itselfThe Field itselfEither of the Either of the aboveaboveDr. BindellDr. BindellElectric PotentialWe will be dealing withWorkEnergy & Conservation Work must be done to move a charge in an electric field.Let’s do a demo ….I need some help.What we will do ….For the moment, assume the charge has MASS. (It may not.)Assume the charge is initially stationary.The charge is to be moved to the left.The charge is to be moved at CONSTANT velocity.+chargeEMr. ExternalMrs. FieldsDuring this process, who is pushing?Mr. ExternalMrs. FieldsDr. BindellWhen we start the process, the charge that is stationary must be brought up to speed.This is work and must be accounted for.This is work but we don’t have to worry about it.Only Dr. Bindell worries about stupid stuff like this!Start and SopENERGY is required to bring the charge up to speed (if it has mass).ENERGY is required to bring the particle back to rest (if it has mass).The sum of these two is ZERO.During this process, who is actually doing work?Mr.