SUNY Geneseo EDUC 488 - Ch 26 Notes

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Current and Resistance Electric Current Yf1 However D A If all points inside a conductor are on the save potential the free electrons move at vanda directions andthusthere is no not transport if we make a break in the conductor ad insert a battery two points A B are on differentpotentials Up Up which relates to the volalg of the battery V VA VB now Now the free electrons inside the conductor move is we define direction and there flow of electric charge which in the sa a net as El chic invent The electric current i dog laurel rate at which chargesflow 51 Until A Acpere Current direction An electric current has the same direction as the Tfg change velocity The sign is defined as follows the carved is due to the notion of is parallel to the 1 R It positive charges the carrel charge velocity E If the carvel negative charges to the charge velocity I is due to tha notion of thy carvel is antiparallel Cave t density Current density is a vector defined as that is I Units E The dive lion of J is the same of the carrel The current cross sectional through a conduitor of area A is give by as that i JA if the carvel density is roustat rousted then i If is not I fj d Resistance iggy we apply a voltage a conductor across i will flow A laurent through thy nonductor V S We define the conductor the ratio resistance as R E SI Unit for R I Omega Ohm Sy bol circuit for can be a resistor in a the mm R 1001 Original Ohn s law Ey X X curved i g i V a b Voltage resistance of the measured length of the arterial wire device Juesis a a Oh law s 304 slow for med students i V N R I 3 R I E E IR Meaning of Ohc s law the the applied voltage with proportionality depends linearly on turret factor R I V inures I n batting t material that follows Ohc s law antitoxin X X f of Isis a We need a to change material force per unit charge f E a curved density J in What is f f tl t cat Hefty one s bio Iforphysicists conductivity sie eye I usitivity frm Csf if Typical values for resistivity t 8 yp Silver Copper Alumina Iron 1 6 10 8 In 1 7 10 8 R 2 8 10 8 R 11 10 8 R Silicon 3 1031 Metals Se iconductors Insulators Glass 1010 10 Im Microscopic F view of Ohc s law g E means accelerate electronsshould the carvel cannot by constant A coastal curved suggests a constant velolity lavs EE t Varg gate tou gushl acceleration ed braking we get a constant velocity but like a resistance is not like dink but elechital a drunk driver nav driver race the electrons already have Because a the additional acceleration and thas tha additional constant velocity is small theveal every large velocity This is called the drift velocity J n Va 9 total charge in a wive with Tha I sun length 2 t the is give by HAL i E MIF uan g the navel density J Afton resistivity with teperatur Variation of For unitals the resitivity increase with temperature We can get an empirial equation go aft To so temperature coefficient ofresitsJiri is reference Temperature usu alle RT is the resistivity al To 5 2 To go exaple for copper g 1 69 10 81 Power in electric circuits TE Ida battery WB a battery is connected to a device If a voltage difference is obseved between the device s couneition points A B Since the battery beeps the potential difference conslet flows tin a charge During idf moves between the terminals dg A and B the potential energy of the charge decreases a carvel It interall a i by du Vdg Vidf in conclude energy has been transferred for Since energy is conserved that the battery The rate is known to the device at which every is transferred as power P dat VEI Vi Sl unit for power P V A Watt U with Ohr slaw Pei v P ER p The kilowatt hour It ed not power of a device with a power of P f a unit of energy is is the work pirlo ed 3600 s a free lhour l ku 1000W in N Pt 1000 3600 W s 3 6 10 J

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