GR9277 #86



Alternate Solutions 
Herminso 20090922 14:33:45  The discharge of the capacitor after it has been charged to is just
,
thus after the switch is opened, since is in series with the capacitor we need to find , which we can determine by how fast the trace sweeps, s. We need to find , will be given. Thus the answer is (B). The ration can be read off the vertical parts of the scope.  

Comments 
ehsana 20131007 17:36:19  Voltage through a discharging capacitor should be .
, as it's written in the solution, is the voltage through a charging capacitor.   astro_girl 20130913 06:30:48  The voltage across the capacitor and acrossR, when the switch is closed, is not but . When the switch is closed the capacitor branch is open , but current keeps flowing through R. This doesn't affect the answer though.   flyboy621 20101022 21:23:15  You can do this one by elimination.
When the switch is opened, R' is out of the picture, which rules out (D). (E) is too vague to be meaningful, so that choice must be wrong. Finally, it should be obvious that will affect only the scale of the scope display and not the timebehavior of it. Thus (A) and (C) are ruled out. (B) is the only choice left.   Herminso 20090922 14:33:45  The discharge of the capacitor after it has been charged to is just
,
thus after the switch is opened, since is in series with the capacitor we need to find , which we can determine by how fast the trace sweeps, s. We need to find , will be given. Thus the answer is (B). The ration can be read off the vertical parts of the scope.   oSciL8 20090329 19:04:58  Wait a minute  I thought the time constant (tau = 1/RC) was dependent on the resistor in series with the capacitor? This would mean that one would need to know the sweep rate and R', not R...would someone explain?
Thanks for this website btw  I'll see how helpful its been in a week!!
gt2009 20090621 04:13:49 
After the switch is opened, R is in series with the capacitor.

  hamood 20070405 14:42:14  Capacitor discharging is V = Vo
Capacitor charging is V(t) = Vo(1)
grace 20101110 22:50:28 
I agree with you.

 

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