ch25_lecture_notes

ch25_lecture_notes - Chapter 25 Capacitors and Dielectrics...

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Chapter 25 Capacitors and Dielectrics In this chapter we will describe devices called “capacitors”. These have the ability to: 1. Store charge and 2. Store energy Capacitors are found in practically all electronic circuits In addition we will examine what happens when we place an insulator (also known as a dielectric ) inside a capacitor (25-1)
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A capacitor is defined as a system of two conductors separated by an insulator (dielectric) Parallel plate capacitor Cylindrical capacitor Spherical capacitor
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Standard symbols for capacitors and batteries
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Capacitance Symbol: C Definition: Where ± Q is the charge on the capacitor plates and V is the potential difference between the two plates. The ratio is a constant Q C V Q V
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The SI unit for the capacitance is the Farad This unit is too large for practical applications. We use instead the following subdivisions: 1 µ F = 10 -6 F 1 nF = 10 -9 F and 1 pF = 10 -12 F The capacitance C is a constant that depends on: 1. The shape , size, and arrangement of the plates 2. The insulator between the plates Q C V 1 (1 ) 1 C F V =
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Parallel Plate Capacitor We will calculate the capacitance of the parallel plate capacitor A = area of the plates d = plate separation o A C d ε =
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Note: C is proportional to the plate area A and inversely proportional to the plate separation d E is the electric field between the plates = o oo o VE d Q E A dQ d Q VC AV A C d σ ε εε = == =
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d L A = L 2 The equation
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ch25_lecture_notes - Chapter 25 Capacitors and Dielectrics...

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