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PY208-Lecture-15

# PY208-Lecture-15 - Physics 208N-004 Lecture#15 16 February...

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When the switch is closed, the capacitor will begin to charge. As it does, the voltage across it increases, and the current through the resistor decreases. Physics 208N-004 Lecture #15 – 16 February 2011 Chapter 26: 5 – RC Circuits 26-5 Circuits Containing Resistor and Capacitor ( RC Circuits) To find the voltage as a function of time, we write the equation for the voltage changes around the loop: Since Q = dI / dt , we can integrate to find the charge as a function of time:

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26-5 Circuits Containing Resistor and Capacitor ( RC Circuits) The voltage across the capacitor is V C = Q / C : The quantity RC that appears in the exponent is called the time constant of the circuit: The current at any time t can be found by differentiating the charge: 26-5 Circuits Containing Resistor and Capacitor ( RC Circuits) Example 26-11: RC circuit, with emf. The capacitance in the circuit shown is C = 0.30 μ F, the total resistance is 20 k , and the battery emf is 12 V. Determine (a) the time constant, (b) the maximum charge the capacitor could acquire, (c) the time it takes for the charge to reach 99% of this value, (d) the current I when the charge Q is half its maximum value, (e) the maximum current, and (f) the charge Q when the current I is 0.20 its maximum value.
If an isolated charged capacitor is connected across a resistor, it discharges: 26-5 Circuits Containing Resistor and Capacitor ( RC Circuits) 26-5 Circuits Containing Resistor and Capacitor ( RC Circuits) Once again, the voltage and current as a function of time can be found from the charge: and

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26-5 Circuits Containing Resistor and Capacitor ( RC Circuits) Example 26-12: Discharging
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PY208-Lecture-15 - Physics 208N-004 Lecture#15 16 February...

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