Physics 212Physics 212yyLecture 9Lecture 9Today's Concept:Today's Concept:Today s Concept:Today s Concept:Electric CurrentElectric CurrentElectric CurrentElectric CurrentOhm’s Law & resistors, Resistors in circuits, Power in circuitsOhm’s Law & resistors, Resistors in circuits, Power in circuits,,,,Physics 212 Lecture 9, Slide Physics 212 Lecture 9, Slide 11MusicWho is the Artist?Who is the Artist?Who is the Artist?Who is the Artist?A)A) Dave BrubeckDave BrubeckB)B)Thelonius MonkThelonius MonkB)B)Thelonius MonkThelonius MonkC)C) Bill EvansBill EvansD)D) Keith JarrettKeith JarrettE)E) Oscar PetersonOscar Peterson•• Now there’s an example of abstract thinking Now there’s an example of abstract thinking ––composing in real time!composing in real time!pgpgpgpg•• Who will be next!?Who will be next!?Physics 212 Lecture 9Physics 212 Lecture 9Some Exam StuffSome Exam Stuff• Exam tomorrw (Wed. Sep. 21) at 7:00 l l ( )– Covers material through lecture 8 (no resistors)– Bring your ID – Conflict exam at 5:15 – you will need to stay in the room until exam ends• Where do I go? EXAM ROOMS (by discussion section)• PreparationPhysics 212 Lecture 8, Slide Physics 212 Lecture 8, Slide 33p– Practice exams– Exam Prep Exercises–Worked examplesYour CommentsYour Comments• “Thank God were are moving on to easier material. Makes my life easier :)”• “I CURRENTly have only a few concerns”• “Can we review for tommorrow's exam?”• “will we have a review section?”• “I was confused with current density”• “Can we do more practice with resistor circuits that have both parallel and series?”• Consider the comments• They help us understand what you are having trouble with•Writing even briefly helps you to think logicallyWriting, even briefly, helps you to think logically•• “I bet you put typos in the “I bet you put typos in the powerpointspowerpoints to make it look like you are to make it look like you are actually using what students wrote, when you are actually writing them. actually using what students wrote, when you are actually writing them. Checkmate!”Checkmate!”Physics 212 Lecture 8, Slide Physics 212 Lecture 8, Slide 44• “Can we look at schematics for electronics we use everyday? Do they have Can we look at schematics for electronics we use everyday? Do they have circuits that look like these?”circuits that look like these?”ELECTRONICS WE USE EVERYDAY (almost) – your iClickerA BIG IDEA REVIEW A BIG IDEA REVIEW Culmb’s LCulmb’s LFCoulomb s LawCoulomb s LawForce law between Force law between point chargespoint charges121,2 1,221,2ˆkq qFrrqq11qq221,2r1,2FElectric FieldElectric FieldGauss’ LawGauss’ LawElectric FieldElectric FieldForce per unit chargeForce per unit chargeFEqElectric FieldElectric FieldProperty of SpaceProperty of SpaceCreated by ChargesCreated by ChargesSuperpositionSuperpositionGauss LawGauss LawFlux through closed Flux through closed surface is always surface is always proportional to proportional to 0encQEdAGauss’ LawGauss’ LawCan be used to Can be used to determine E field determine E field SpheresSpheresCylindersCylindersInfinite PlanesInfinite Planesppppppppcharge enclosedcharge enclosed0determine E field determine E field Infinite PlanesInfinite PlanesElectric PotentialElectric PotentialPotential energy per Potential energy per bbaldEUVElectric PotentialElectric PotentialScalar Function that Scalar Function that VEPotential energy per Potential energy per unit charge unit charge abaldEqVScalar Function that Scalar Function that can be used to can be used to determine Edetermine EVECapacitanceCapacitanceQPhysics 212 Lecture 9, Slide Physics 212 Lecture 9, Slide 6605Relates charge and Relates charge and potential for two potential for two conductor system conductor system QCVAPPLICATIONS OF BIG IDEAS APPLICATIONS OF BIG IDEAS Cndut sCndut sConductorsConductorsCharges free to Charges free to movemoveWhat Determines What Determines How They Move?How They Move?They move until They move until E = 0 !!!E = 0 !!!E = 0 in conductor E = 0 in conductor determines charge determines charge densities on surfacesdensities on surfacesSpheresSpheresCylindersCylindersInfinite PlanesInfinite PlanesGauss’Gauss’LawLawField Lines & Field Lines & EquipotentialsEquipotentialsCapacitor NetworksCapacitor NetworksWork Done By E FieldWork Done By E FieldbababaldEqldFWppaabChange in Potential EnergyChange in Potential EnergySeries:Series:(1/C(1/C2323)=(1/C)=(1/C22)+(1/C)+(1/C33))Physics 212 Lecture 9, Slide Physics 212 Lecture 9, Slide 7705bababaldEqWUParallelParallelCC123123= C= C11+ C+ C2323Key Concepts for Today:Key Concepts for Today:1)1) How resistance depends on A, L, How resistance depends on A, L, , , 2)2) How to combine resistors in series and parallelHow to combine resistors in series and parallel3)3) Understanding resistors in circuitsUnderstanding resistors in circuitsToday’s Plan:Today’s Plan:1)1) Review of resistance & preflightsReview of resistance & preflights2)2)Work out a circuit problem in detailWork out a circuit problem in detail))ppPhysics 212 Lecture 9, Slide Physics 212 Lecture 9, Slide 88IIAALLLLV V Ohm’s Law: JOhm’s Law: J= = EEConductivity Conductivity –– high for good conductors.high for good conductors.V = ELV = ELI JAI JAObservables:Observables:I/A = I/A = V/LV/LI = V/(L/I = V/(L/I = JAI = JA V/(L/ V/(L/R=R=L L I = V/RI = V/RR = ResistanceR = ResistancePhysics 212 Lecture 9, Slide Physics 212 Lecture 9, Slide 99R = R = A A I = V/RI = V/RR ResistanceR Resistance = 1/= 1/This is like plumbing!This is like plumbing!II is like flow rate of wateris like flow rate of waterVVis like pressureis like pressureVV pr ur pr urRR is how hard it is for water to flow in a pipe is how hard it is for water to flow in a pipe R =R =LLTo make To make RR big, make big, make LL long or long or AA smallsmallR =R =AAT mk T mk RRsm ll m k sm ll m k LLsh t sh t AAbibiTo make To make RRsmall, make small, make LLshort or short or AAbigbigPhysics 212 Lecture 9, Slide Physics 212 Lecture 9, Slide 1010Checkpoint 1aCheckpoint 1a Checkpoint 1bCheckpoint 1bSame current