(a) Calculate the charge on the positive plate of the capacitorjust after the sw
ID: 1671746 • Letter: #
Question
(a) Calculate the charge on the positive plate of the capacitorjust after the switch is closed.
Q(0+) = C *
0 OK
HELP: Can the charge on a capacitorchange discontinuosly?
(b) Calculate the following currents immediately after theswitch is closed.
I1(0+) = A *
.122 OK
I2(0+) = A *
0 OK
(c) After the switch has been closed for a long time, calculatethe following quantities.
I1 = A *
.042 OK
I2 = A *
.042 OK
Q = C *
3.29E-5 OK
(d) At some yet later time T, the switch is againopened. Calculate the following currents immediatelyafterward.
I1(T+) = A *
0 OK
I3(T+) = A
0 NO
HELP: At time T (justbefore the switch is opened), what is the voltage across thecapacitor? Can the charge on the capacitor change in theinfinitesimal time it takes to open the switch?
HELP: Write down Kirchoff's Laws forthe circuit when the switch is open at time T+, given thatyou know the voltage across the capacitor at this time.
(e) What is the time constant of the dischargingcircuit?
t = s
.0003 NO
HELP: Redraw the original circuit,discarding all circuit elements thataresuperfluous after the switchis opened
E = 5 VR1 = 41 W
R2 = 79 W
C = 10 µF
Explanation / Answer
d. Current I3 (T+ ) = VC /R2 Here voltageacrosscapacitor VC = Q/ C = 3.29* 10-5 / 10 * 10-6 = 3.29 V I3 (T +) = 3.29 / 79 = 4.16* 10-2 A = 3.29 V I3 (T +) = 3.29 / 79 = 4.16* 10-2 A e. Once the switch is open,the circuit contains only C and R2. Time constant of discharging circuit = R2* C = 79* 10 * 10-6 = 7.9* 10-4 s = 7.9* 10-4 sRelated Questions
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