ENGR 111 Lecture
7
Reading: Chapters 20,21,30
Class notes
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Fall 2004
Capacitance
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Two conducting plates, separated by an
insulator
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Can’t pass through current continuously, but
current can pass for a short time
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Current charges one plate, equal, opposite charge
builds on the other plate, allowing current to pass
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Q = CV, I = dQ/dt = C dV/dt
Fall 2004
Capacitance – Water Analogy
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As water enters one end – compresses the
spring, exerting pressure on other end
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Amount of water entering one side equals
leaving on other side
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RC Circuits
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RC product determines the behavior
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RC = time constant
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Within RC time units, current is 1/e of
initial current etc…