First, draw the diagram. (I wish I got paid a dollar every time I
told a student to draw the diagram. My powers of visualization are
better than theirs, yet *I* find the diagrams helpful ... surely
they would find them at least as helpful....)
I
____>>>________ V
| |
| Z
-------- Z
-------- Z
| Z
|___________|___
|
///
V = Q/C capacitor law
V = I R resistor law (Ohm's law)
Q/C = I R equating equals to equals
--or--
Q/C - I R = 0 Kirchhoff's loop law, with due regard to signs
dQ/dt = -I current is flowing _out_ of the capacitor
dQ/dt = -Q / R C plugging in
Q = Q0 exp(-t / R C) integrating
I
____<<<________ V
| |
| Z
-------- Z
-------- Z
| Z
|___________|___
|
///
V = Q/C capacitor law
V = - I R resistor law (Ohm's law) ... with unconventional
assignment of direction of current
Q/C = - I R equating equals to equals
--or--
Q/C - I R = 0 Kirchhoff's loop law, with due regard to signs
dQ/dt = I current is flowing _into_ the capacitor
dQ/dt = -Q / R C plugging in
Q = Q0 exp(-t / R C) integrating
============
I hope you appreciate the importance of the diagram in clarifying
the relationship between V, I and dQ/dt.
If that doesn't answer the question, please re-ask.