So, I understand the charging of an RC circuit perfectly, but I am a tiny bit bothered by one part of the formulation of charge on a capacitor plate as a function of time for a discharging capacitor in a simple RC circuit (charged with one battery, one resistor and one capacitor all in series and discharged without the battery).(adsbygoogle = window.adsbygoogle || []).push({});

What bothers me is that the original loop rule equation seems to have a negative sign that doesnt make sense. The book gives the expression

-q/C-IR=0

I don't understand why both of these should be negative, in looking at the direction that the charge would flow, it seems that the equation should be

q/C-IR=0 or IR-q/C=0

The books explanation is that the formula is the same as the one used for charging the capacitor just without the battery, but this explanation doesnt quite make sense to me. I'm probably just being stupid. Is the reason perhaps that the -IR involves a negative value for I and therefore causes a positive potential difference?

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# Homework Help: Quick RC circuit question

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