PowerPoint PresentationSlide 2Energy Stored in a CapacitorSlide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Charge Carrier Motion in a ConductorSlide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Temperature Variation of ResistivityTemperature Variation of Resistivity, contSlide 22Electrical Energy and PowerElectrical Energy and Power, contElectrical Energy and Power, finalPhysics 213General PhysicsLecture 502Last Meeting: CapacitanceToday: Current and ResistanceEnergy Stored in a CapacitorEnergy stored = ½ Q ΔVFrom the definition of capacitance, this can be rewritten in different formsC2QVC21VQ21Energy224NCCCCCeqeq ...111221VCEnergy NCCCCCeqeq ...C CCCQuiz: The plates of a connected parallel-plate capacitor of capacitance C are brought together to one-third their original separation. The energy stored is now (a) W/9(b) W/3(c) 3W(d) 9WAnswer: c221 1, 2 2QW CV WC= =QUICK QUIZ 16.6A fully charged parallel-plate capacitor remains connected to a battery while you slide a dielectric between the plates. Do the following quantities increase, decrease, or stay the same? (a) C; (b) Q; (c) E between the plates; (d) V.QUICK QUIZ 16.6 ANSWER(a) C increases(b) Q increases(c) E stays the same (d) V remains the same8910Charge Carrier Motion in a ConductorThe zig-zag black line represents the motion of a charge carrier in a conductorThe net drift speed is smallThe sharp changes in direction are due to collisionsThe net motion of electrons is opposite the direction of the electric fieldCharge Carrier Motion in a ConductorThe drift speed Vd is small (~1meter/hour) The fermi speed Vf is very fast! Due to quantum mechanics of electrons. (~106 meters/second) Charge rearrangements and signals travel near speed of light (~108 meters/second) fv13141516171819Variety of ResistorsTemperature Variation of ResistivityFor most metals, resistivity increases with increasing temperatureWith a higher temperature, the metal’s constituent atoms vibrate with increasing amplitudeThe electrons find it more difficult to pass through the atomsfvTemperature Variation of Resistivity, contFor most metals, resistivity increases approximately linearly with temperature over a limited temperature rangeρ is the resistivity at some temperature Tρo is the resistivity at some reference temperature To To is usually taken to be 20° C is the temperature coefficient of resistivity)]TT(1[oo22Energy is turned to heat (random motion)Electrical Energy and PowerThe rate at which the energy is lost is the powerFrom Ohm’s Law, alternate forms of power areQV I Vt 22VI RR Electrical Energy and Power, cont22VI RR Electrical Energy and Power, finalThe SI unit of power is Watt (W)I must be in Amperes, R in ohms and V in VoltsThe unit of energy used by electric companies is the kilowatt-hourThis is defined in terms of the unit of power and the amount of time it is supplied1 kWh = 3.60 x 106
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