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## General Physics

by: Nichole Keebler

11

0

7

# General Physics PHYSICS 104

Nichole Keebler
UW
GPA 3.95

Stephen Burns

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COURSE
PROF.
Stephen Burns
TYPE
Class Notes
PAGES
7
WORDS
KARMA
25 ?

## Popular in Physics 2

This 7 page Class Notes was uploaded by Nichole Keebler on Thursday September 17, 2015. The Class Notes belongs to PHYSICS 104 at University of Wisconsin - Madison taught by Stephen Burns in Fall. Since its upload, it has received 11 views. For similar materials see /class/205212/physics-104-university-of-wisconsin-madison in Physics 2 at University of Wisconsin - Madison.

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Date Created: 09/17/15
RC Circuit Analysis Circuit with resistance and capacitance Charging and discharging ProblemSolving Strategy Kirchhoff s Rules Draw the circuit diagram and assign labels and symbols to all known and unknown quantities Assign directions to the currents Apply the junction rule to any junction in the circuit Apply the loop rule to as many loops as are needed to solve for the un nowns Solve the equations simultaneously for the unknown quantities Exa mple In the circuit below your are given E E R R2 and R3 d 13 Find1 12 an J1 Label all currents Choose any direction J2 Label Ifor all elements Current goes 3 Choose loop and direction Your choice rl e own vo age rops lrS Slgn you I IS Slgn ouse rA W39td lt d F39t39 h39t39 39 t rl e own no e equalon 5 W39t d d t39 Lnnp 1 eE1IRrIR o R r l Lnnp z 1212 13R3Fq 0 Nude I L I1 3 Equations 3 unknowns the rest is algebra 9mm What is the resistance of a capacitor Answer depends on time Uncharged Initially voltage drop between he plates is zero The charges ow in and build up on the plates Resistance starts off 39om zero RD V 0 l 0 Fully charged Charge on the plates builds to a maximum No more current ow Voltage reaches a maximum Resistance approaches in nity RM V VO oo Combine RC Circuits Gives time dependence Current is not constant lt Charge on the capacitor is not constant qt Used for timing Pacemaker Intermittent windshield wipers Models nervous system Olympic Trivia How soon after starting gun can you run wo getting a False Start 01 seconds RC Circuits Charging The switches are originally open and the capacitor is uncharged Then switch S1 is closed Kircho s Voltage Rule VtRqtC o Just alter 31 closing qqn 0 v IUR0 ID v IR Long time alter la0 v qmC 0 qfv c Intermediate more complex q rimem lt heatRC Charging in an RC Circuit The charge on the capacitor varies with time I q Q1elRC The time constant rRC The time constant represents the time required for the charge to increase from zero to 63 2 of its maximum 92904 UWi can in PM it 104 Fall 2003 7 Discharging in an RC Circuit When a charged capacitor is placed in the circuit it can be discharged I q QetRC The charge decreases exponentially Q AttTRC the charge decreases to 0368 Qmax 036m In other words In one I time constant the capacitor loses 632 of 7 its initial charge 92904 UWi can in PM it 104 Fall 2003 Preflight Short Term Both switches are initially open and the capacitor is uncharged What is the current through the battery just after switch S1 is closed 1 lb0 2 bVI3R l IWn 1m m quot1 will 5m 4 lb VIR KVL v 2R qC o q 0 s I V2R 92904 UWi can in PM it 104 Fall 2003 9 Preflight Long Time Both switches are initially open and the capacitor is uncharged What is the current through the battery after switch 1 has been closed a long time R 39 2 bVI3R 3 bVI2R 4 bVIR v 2 69 S 1 Long time gt current through capacitor is zero lb0 because the battery and capacitor are in series KVL vo qWIC0 qO VC 92904 UWi can in PM it 104 Fall 2003 Preflight Discharge After being closed for a long time the switch 1 is opened while switch 2 is closed simultaneously What is the current through the resistor R 1 R0 R 39 2 R VI3R m 3 R VI2R w l V S St Long time gt capacitor is fully charged to V Switch 1 open switch 2 closed means C discharges through R KVRVRR0qWVC 92904 UWi can In PM it 104 Fall 2003 11 Charging Intermediate Times Calculate the charge on the capacitor 3gtlt1O393 seconds after switch 1 is closed R 10 9 V 50 Volts C 10ch lt10 quaem q 1e3gtlt1039320gtlt100gtlt10396 qm 0 78 Recall q V C 50100x106 0 78 3 9 X10393 Coulombs 92904 UWi can in PM it 104 Fall 2003 Electrical Safety Electric shock can result in fatal burns Electric shock can cause the muscles of vital organs such as the heart to malfunction The degree of damage depends on the magnitude of the current the length of time it acts the part of the body through which it passes 92904 UWisconsin Physics 104 Fall 2003 13 Effects of Various Currents 5 mA or less can cause a sensation of shock generally little or no damage 10 mA hand muscles contract may be unable to let go a of live wire 100 mA if passes through the body for 1 second or less can be fatal 92904 UWisconsin Physics 104 Fall 2003 14 Ground Wire Electrical equipment manufacturers use electrical cords that have a third wire called a ground Prevents shocks 2003 Thomson 4 Brooks Cole m 92904 UWisconsin Physics 104 Fall 2003 15 Ground Fault Interrupts GFI Special power outlets Used in hazardous areas Designed to protect people from electrical shock Senses currents of about 5 mA or greater leaking to ground Shuts off the current when above this level 92904 UWisconsin Physics 104 Fall 2003 16 Electrical Signals in Neurons Specialized cells in the body called neurons form a complex network that receives processes and transmits information from one part of the body to another Three classes of neurons Sensory neurons 0 Receive stimuli from sensory organs that monitor the external and internal environment of the body Motor neurons 0 Carry messages that control the muscle cells lnterneurons Transmit information from one neuron to another 92904 UWisconsin Physics 104 Fall 2003 17 Diagram of a Neuron l l Synapse R C Nucleus quot Signals lrmn an 1 h I 11 euro 1 Dc ndritcs Cell body Axon Nerve endings 2003 Thomson v Brooks Cole 92904 UWisconsin Physics 104 Fall 2003 18 Physics 104 Lectu Electric Power EMF amp lntemal Resistance DC Resistor Circuits Resistors in Series Resistors in Parallel Circuit Analysis Electrical Hazards mm mm mi sismm Electrical Powe Power Dissipated in a Electric energy depends on b drop and charge moved PE 7E7 Force x Distance re5 r resistor oth voltage qV P 2 I m J 2 r PLVW I I 2 p V12R R m unmmismm emf amp Internal Resistance The seiuree that rnaintainsthe eurrent in a eieised eireuitis eaiied a seiuree ufemf circulating in eneuis are sduiees uternt s Examplesbatteriesgtgeneiatuis Si units are veiits s emiiswuikdune per unit charge Real battery has surne internai resistanee Therereiretheterrninaiyeiitage is net eduaitei the ernr mm mm mi sismm lLiili ri Xumiir Energy Transfer in the Circuit Imagine a quantity of positive char e AQ moving around the circuit from point A back point A As the charge moves through i l m A to B the lt As the cha e moves through C D it the atoms ofthe resistor mm summit mi sismm 2 Electrical Energy amp Power The rate at whieh the Energy is lustisthe puvver Frum Ohm s Lavv aiternate rdrrns at power are The Si unit at quErisWatt W 7 i must be in Ampeies R in ohms and AVin Volts Unit at Energy used by eieetrie eurnpanies is the kilowallrhour 7 De ned in teirns utthe unit utpuwei and arnuunt uttirne it is supp ed 7 i kWiTZCiEEI MEISJ mm summit mi sismm i nternal Resistance T s 7quot Terminal volts AV Vb a AV i r For the entire circuit IR r I i equals terminal voltage when current is zero DpEnrcirEuit yuitage hen R gtgt r r can be ignored iGeneraiiy assumed in preihierns uniess eitherWise stated Power relationship I 8 I2 R Z I39 When R gtgt r most ofthe power delivered by the battery is transferred to the load res39stor mm summit mi sismm t Reswstorsm SeHeS Reswstorsm Senes On2wwe Onewwe Emmewamgmg engths damage WWW ane ream s mmmamssm quotW W W 239 v Vq w 39 A115 Vi R z R 7 mg a age 2R R ow m om n ma ng enw w R R my O ueshon m unth Wm mm arman maqu m mw mm mo s 1 rm m 5 1mm unth n 9a Senes EXamp e Res storsm ParaHe mm mm mm 1 vans V 11 Twu Wwes E e we v admng We Ales mm m m a m S MWWW J I quota Wm 2xmmvulx Y m cm WWW nu Resistors in Parallel Twu lees am endsalveslslm ave mrmeded Add 1qu lRquot ma mngcwem vmlovmfvmmm m a 4111am v vaw Question As mm and mm 1mm ave added 1 m pavallel 1mm clvcull shuwn have manna bemeenlhe p lhelulal 12s mls and O rlncreases V 1 Parallel Example nm1ucnmmmmw Smyle w m 17 mm IIMl mm 1m mum h 1515mmquot mm 5 closed 1 1mm 2 I 3 Decvexs mmWm va1mwmmuwmmw 2 Remalmsame 1 u 1 1 3 Decveass V 2 3 Jammy Danga mm use one Dawer 511mm mms myowaveam aavvh SEEhaHJoasen am gunaranvlmerall m oneomlal thslsda lgemushscmse a 1111 Wm n m n 1 Yhe 155mg m We mm cram 151 m 2 Yhevul azeawosslhe urwmsloo m mm Yhe Mm 1n lhe mm umun 151 m Pre ighl 58 R 2R Wm camwmahan mm m 551mg 1 2 t 3 f 1 3 r w 1ms

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