When Is the Potential Across a Capacitor Equal to That Across a Resistor?

[Gabe805]

Homework Statement

.
Switch http://edugen.wileyplus.com/edugen/courses/crs7165/halliday9781118230725/c27/math/math152.gif in Fig. 27-63 is closed at time http://edugen.wileyplus.com/edugen/courses/crs7165/halliday9781118230725/c27/math/math164.gif, to begin charging an initially uncharged capacitor of capacitance 15 microfarads through a resistor of resistance 20 ohms. At what time is the potential across the capacitor equal to that across the resistor?
http://edugen.wileyplus.com/edugen/courses/crs7165/halliday9781118230725/c27/image_n/w1548-nn.png
Figure 27-63
Problems 57 and 96

Homework Equations

v=vmax(1-e^-(t/RC))
V=iR
i=imax(e^-(t/RC))[/B]

The Attempt at a Solution

The answer winds up being .208 ms. so I am just looking for an answer. I want to know how to solve this. I tried using ohms law to figure out what the voltage is across R but of course that was a dead end because the emf is not given. next I tried iR=vmax(1-e^-t/RC). Again a dead end. Also I know that when the capacitor is fully charged the current is zero, hence the voltage across R will also be zero but I couldn't figure out how to implement that knowledge into a solution. Any help would be greatly appreciated.[/B]

 

[SteamKing]

None of the links to your figures are working.

 

[Gabe805]

I just uploaded another pic. In case that one doesn't work, the circuit is just an RC series circuit with a battery and a switch.