chapter26_2class

chapter26_2class - Capacitance, Capacitors and Circuits....

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Capacitance, Capacitors and Circuits. Start with a review The capacitance C is defined as V Q C To calculate the capacitance, one starts by introduce Q to the object, and use the Laws we have so far to calculate for the ΔV .
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Example: Capacitance of a Cylindrical Capacitor Step 1: introduce Q to the rod (radius a ) and – Q to the shell (inner radius b ): E Step 2: Use Gauss’s Law to calculate the electric field between the rod and the shell to be (see the example in Gauss’s Law chapter): r E ˆ r l Q 0 2 πε = Step 3: Calculate for ΔV : ) ln( 2 2 0 0 a b l Q dr r d V b a l Q b a = = = r E Step 4: Capacitance is ) ln( 2 a 0 b l V Q C =
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More on the review Capacitance of a parallel plate capacitor d A C 0 ε = The electric energy stored in a capacitor 2 2 ) ( 2 1 2 V C C Q U E = = A question: why C here is not a function of ΔV while U E is? The dielectrics in a capacitor: vacuum C C = κ
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Circuit and Its Symbols A circuit diagram is a simplified representation of an actual circuit Circuit symbols are used to represent the various
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chapter26_2class - Capacitance, Capacitors and Circuits....

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