boogyman19946
- May 2, 2011
- 38
- Joined
- May 2, 2011
- Messages
- 38
In a book I'm reading (and kind of trying to employ as I go), I'm finding a certain concept concerning capacitors hard for me to figure out.
The book presents a circuit that comprises of two components: a capacitor and a resistor in a series loop (that is, they are connected to each other with both ends). I figure the capacitor starts out fully charged.
The book states that using capacitor rules, the following can be derived:
C(dV/dt) = I = -V/R
where C is the capacitance of the cap, dV/dt is the change in voltage, I is the current, V is the voltage, and R is the resistance of the capacitor.
So the I = -V/R equations looks a little like Ohm's Law, but all calculations afterwards rely on the fact the ratio V/R is negative, whereas Ohm's Law is not. I suspect that the book is trying to maintain the right "direction" of current so when a voltage is reduced from a charged cap, it's going to provide "negative voltage." But the circuit makes no mention of any voltage being taken away. It doesn't even say the cap is charged. It just presents the circuits, doesn't give any starting conditions, writes out some formula and kind of relies on the reader to either take a leap of faith or go on a forum to ask the pros ^.^
That being said, my question is mainly this: How come I = -V/R and not I = V/R ?
The book presents a circuit that comprises of two components: a capacitor and a resistor in a series loop (that is, they are connected to each other with both ends). I figure the capacitor starts out fully charged.
The book states that using capacitor rules, the following can be derived:
C(dV/dt) = I = -V/R
where C is the capacitance of the cap, dV/dt is the change in voltage, I is the current, V is the voltage, and R is the resistance of the capacitor.
So the I = -V/R equations looks a little like Ohm's Law, but all calculations afterwards rely on the fact the ratio V/R is negative, whereas Ohm's Law is not. I suspect that the book is trying to maintain the right "direction" of current so when a voltage is reduced from a charged cap, it's going to provide "negative voltage." But the circuit makes no mention of any voltage being taken away. It doesn't even say the cap is charged. It just presents the circuits, doesn't give any starting conditions, writes out some formula and kind of relies on the reader to either take a leap of faith or go on a forum to ask the pros ^.^
That being said, my question is mainly this: How come I = -V/R and not I = V/R ?