Electrical Conduction Electrodynamics 10 20 14 9 19 AM Electrodynamics free electrons that are moving in conductors Assumptions about conductors E 0 is no longer true E 0 in conductors NOW because the charges have to move o Electric field is required for charges to move Current is net amount of charge that passes through a given This flow of charges is current surface per unit time Units of current coulombs second Amperes A Typically computers information current is a few microamps For energy transfer current is milliamps to amps We can view I as a vector along the direction of the hypothetical positive charges basically it flows opposite to the electron flow negative charges Current density j is current per perpendicular cross sectional area in a conductor seen as a vector in the direction of I current If current is uniformly distributed then I j A o if j varies over cross section NOTE A is the perpendicular cross sectional area perpendicular to the current Inside conductor E 0 Does this imply that F q E e E therefore does a e E m NO because in conductors the charges are stuck in the conduction band and are slowed down by the metal so they are NOT FREE o The ions impede the flow of electrons conductors have resistance because the electrons are attracted to the ions and the flow is slowed In conductors electrons reach terminal velocity called Drift velocity o Number density electrons per volume estimate Overview Resistors o Resistance is an extrinsic property Resistivity Intrinsic o Related to local electrical properties o o Relationship between resistance and resistivity Ohm s Law not universal just valid in some specific cases For some circumstances it is observed that V is increased current increases proportionally o o Dr Sandhu Office Hours Tuesday 11 30 12 30 Thursday 1 30 2 30 Monday march 8 5 00pm and Friday March 12 5 00pm Energy transfer and electrical heating Heat generated in a system due to resistance o When electrons go through conductors they experience friction which causes heat
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