Solving Discharging Circuit Homework

[driedupfish]

Homework Statement

http://online.physics.uiuc.edu/cgi/courses/shell/common/showme.pl?courses/phys212/oldexams/exam2/fa06/fig17.gif
After a very long time with both switches in the closed position, switch S2 is reopened. How long does it take for the charge on capacitor C2 to drop to 1/e (36.8%) of its fully-charged value (i.e. of the value it had just before S2 was reopened)?

Homework Equations

Time constant = RC

The Attempt at a Solution

I try to find the total resistance, but am not sure how. I am not even sure what it means by "drop to 1/e (36.8%)". Does it mean 36.8% of the total charge?

 

[Pythagorean]

Homework Statement

http://online.physics.uiuc.edu/cgi/courses/shell/common/showme.pl?courses/phys212/oldexams/exam2/fa06/fig17.gif
After a very long time with both switches in the closed position, switch S2 is reopened. How long does it take for the charge on capacitor C2 to drop to 1/e (36.8%) of its fully-charged value (i.e. of the value it had just before S2 was reopened)?

Homework Equations

Time constant = RC

The Attempt at a Solution

I try to find the total resistance, but am not sure how. I am not even sure what it means by "drop to 1/e (36.8%)". Does it mean 36.8% of the total charge?

yes, since charge is a function of voltage here. As the voltage drops, less charge is accumulated on the plates of the capacitor.

 

[driedupfish]

Okay, to find the time constant, RC, I have to find the equivalent resistor at that point. But I don't know how? With only S2 reopened, are all the resistors now in parallel?