a calculus/physics question...

[ptown]

hello all,

i think my question has closer ties to mathematics that's why im posting here.

how do i interpret this \DeltaV= q/C ?

"Physics for Scientists and Engineers" (Serway, 6th ed, pg 807).

i've encountered it a few times in physical chemistry and I believe it has to do with differentiation. the example given is the potential difference across a capacitor and q is the charge on the capacitor at some instant during the charging process.

my confusion specifically is that the symbol for charge is divided by the unit of charge.

if someone could explain this or give me a search term so I could find why this is so it will be greatly appreciated.

thanks...

[vector22]

That equation is saying that an incremental increase in voltage across the capacitor has occured in an increment of time. The time factor is because a steady charging current of one ampere into a capacitor of one Farad will increase the voltage acrcrss the capacitor at one volt per second.

If you carrry out some additional math on that equation you will arrive at the voltage across the capacitor at any time as it is being charged. For a series resistive capacitive ciruit the charging current decreases exponentially (i t's been a couple years since i did this kind of math)

[tiny-tim]

hello ptown! welcome to pf! :smile:
my confusion specifically is that the symbol for charge is divided by the unit of charge.

ah, no …

the "C" isn't "coulomb", it's "capacitance", the ratio of how much charge you get for your difference in voltage across a capacitor ! :wink:

[ptown]

thank you both for replying...

the "C" is for "capacitance" cleared it up for me.

i have another question. although the subject is different I think the mathematical idea is similar.


Question:

If an isobaric vapor deposition process is known to have the following temperature dependence for \DeltaG,

\DeltaG(J) = 127.5T - 34.6 (T is in Kelvin)

Calculate \DeltaS (J/K)


i have a fairly good understanding of thermodynamics. so, i believe my inability to solve this is due to my not understanding the math; it appears to be a strait-forward question. if its not the math I apologize and will move my thread to another forum.

note: this is a question I got wrong last semester. i.e. i'm not trying to get anyone to do my work for me i just want to understand.

thanks again...