# SMU PHYS 1304 - Resistance, Capacitance and Inductance (22 pages)

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## Resistance, Capacitance and Inductance

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## Resistance, Capacitance and Inductance

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Lecture Notes

Pages:
22
School:
Southern Methodist University
Course:
Phys 1304 - Introductory Electricity and Magnetism
##### Introductory Electricity and Magnetism Documents

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Chapter 32 Inductance L and the stored magnetic energy RL and LC circuits RLC circuit Resistance Capacitance and Inductance DV Ohm s Law defines resistance R I Resistors do not store energy instead they transform electrical energy into thermo energy at a rate of DV 2 P DV I I 2 R R Q C DV Capacitance the ability to hold charge Capacitors store electric energy once charged 1 Q2 1 2 DU E C DV 2 C 2 Inductance the ability to hold current moving charge Inductors store magnetic energy once charged with current i e current flows through it Inductance the definition When a current flows through a coil there is magnetic field established If we take the solenoid E m0 nIcoil assumption Bfor the When this magnetic field flux changes it induces an emf EL called self induction d NAB d NAm0 nI dF B dI E mn 2V L dt dt dI or EL L dt dt 0 dt I EL L For a solenoid L m0 n 2V dI dt Where n of turns per unit length N of turns in length l A cross section area V Volume for length l This defines the inductance L which is constant related only to the coil The selfinduced emf is generated by current flowing though a coil According to Lenz Law the emf generated inside this coil is always opposing the change of the current which is delivered by the original emf Inductor We used a coil and the solenoid assumption to introduce the inductance But the definition L EL dI dt holds for all types of inductance including a straight wire Any conductor has capacitance and inductance But as in the capacitor case an inductor is a device made to have a sizable inductance An inductor is made of a coil The symbol is Once the coil is made its inductance L is defined The self induced emf over this inductor under a changing current I is given by dI EL L dt Unit for Inductance The SI unit for inductance is the henry H V s 1H 1 A Named for Joseph Henry 1797 1878 American physicist First director of the Smithsonian Improved design of electromagnet Constructed one of the first motors Discovered self inductance

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