Transcript Document
Admin:
• Assignment 8 is posted • Due Monday • Note that the phase angle for the last question is given
in radians
• Second mid-term date is Wednesday May 6 th
These are in radians
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e -
v R
-
v C
= 0
This is the one I ’ll give you on the formula sheet
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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 Ω, and the battery emf is 12 V. Determine
The maximum charge is the
emf
× C = 3.6 μC.
(d) the current
I
when the charge
Q
maximum value, is half its (e) the maximum current, and (f) the charge
Q
maximum value.
when the current
I
is 0.20 its
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e
Q
=
v R
(
t
) -
v C C v C
(
t
) = 0
How about this one?
Find an expression for the voltage across the capacitor Find an expression for the current through the battery
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How about this one?
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or this one?
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or this one?
or this one?
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So which will charge faster?
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and this one?
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and this one?
Discharging a capacitor If an isolated charged capacitor is connected across a resistor, it discharges:
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Discharging a capacitor 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
RC
circuit.
In the
RC Q
0 = C E
.
circuit shown, the battery has fully charged the capacitor, so Then at
t
= 0 the switch is thrown from position a to b . The battery emf is 20.0 V, and the capacitance
C
= 1.02 μF. The current
I
is observed to decrease to 0.50 of its initial value in 40 μs.
(a) What is the value of
Q
, the charge on the capacitor, at
t
= 0? (b) What is the value of
R
? (c) What is
Q
at
t
= 60 μs?
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26-5 Circuits Containing Resistor and Capacitor (RC Circuits) Conceptual Example 26-13: Bulb in
RC
circuit.
In the circuit shown, the capacitor is originally uncharged. Describe the behavior of the lightbulb from the instant switch S is closed until a long time later.
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26-5 Circuits Containing Resistor and Capacitor (RC Circuits) RC circuits are often used when timing is important.
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26-5 Circuits Containing Resistor and Capacitor (RC Circuits) RC circuits are often used when timing is important.
Windshield wipers Clocks/ Oscillators Digital Voltmeter Security light Heating systems
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