Chapter 32 - Ch32Inductance.notebook August06,2010...

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Ch32 Inductance.notebook 1 August 06, 2010 Aug 4­10:54 AM Chapter 32 Inductance Aug 4­10:54 AM Chapter Outline 32.1 Self­ Induction and Inductance 32.2 RL Circuits 32.3 Energy in a Magnetic Field 32.4* Mutual Inductance 32.5 *Oscillations in an LC Circuit 32.6 *The RLC Circuit Aug 4­10:54 AM Some Terminology Use emf and current when they are caused by batteries or other sources Use induced emf and induced current when they are caused by changing magnetic fields When dealing with problems in electromagnetism, it is important to distinguish between the two situations Aug 4­10:54 AM Self­Inductance When the switch is closed, the current does not immediately reach its maximum value Faraday’s law can be used to describe the effect Aug 4­10:54 AM Self­Inductance, 2 As the current increases with time, the magnetic flux through the circuit loop due to this current also increases with time This increasing flux creates an induced emf in the circuit Aug 4­10:54 AM Self­Inductance, 3 The direction of the induced emf is such that it would cause an induced current in the loop which would establish a magnetic field opposing the change in the original magnetic field The direction of the induced emf is opposite the direction of the emf of the battery This results in a gradual increase in the current to its final equilibrium value
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Ch32 Inductance.notebook 2 August 06, 2010 Aug 4­10:54 AM Self­Inductance, 4 This effect is called self­inductance Because the changing flux through the circuit and the resultant induced emf arise from the circuit itself The emf ε L is called a self­induced emf Aug 4­10:54 AM Self­Inductance, Equations An induced emf is always proportional to the time rate of change of the current The emf is proportional to the flux, which is proportional to the field and the field is proportional to the current L is a constant of proportionality called the inductance of the coil and it depends on the geometry of the coil and other physical characteristics Aug 4­10:54 AM Inductance of a Coil A closely spaced coil of N turns carrying current I has an inductance of The inductance is a measure of the opposition to a change in current Aug 4­10:54 AM Inductance Units The SI unit of inductance is the henry (H) Named for Joseph Henry Aug 4­10:54 AM Inductance of a Solenoid Assume a uniformly wound solenoid having N turns and length ℓ Assume ℓ is much greater than the radius of the solenoid The flux through each turn of area A is Aug 4­10:54 AM Inductance of a Solenoid, cont The inductance is This shows that L depends on the geometry of the object
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Ch32 Inductance.notebook 3 August 06, 2010 Aug 4­10:54 AM RL Circuit, Introduction A circuit element that has a large self­ inductance is called an inductor The circuit symbol is We assume the self­inductance of the rest of the circuit is negligible compared to the inductor
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Chapter 32 - Ch32Inductance.notebook August06,2010...

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