What is the Charging Capacitor formula?????

Thread Starter

Ladies_Man

Joined Jul 28, 2007
4
In my textbook,.. the formula is given by VC(t) = VS(1-e-t/ t)

Where does the (e) come from????

PLEASE HELP...

and if any of u got any alternate formula.,, feel free to write it down...

THANKS
 

BrianH

Joined Mar 21, 2007
43
Hello there.

e is a very special number which occurs in nature. It represents an exponential growth and is approximately equal to 2.135675x10-3.

Whether e is a problem for you depends on what you're looking to get out of that equation. If you want the answer to VC or VS and you know all of the other parameters then you're fine. Just work out -t/rc, save the answer and then press the ex button on your calculator and recall the answer to -t/rc. This will give you the answer to the e-t/rc bit and the rest should be easy.

If your unknown is in the -t/rc part of the equation then it's a little more complicated because you'll need to get rid of the e before you can get an answer. In this case you would need to transpose the equation so you get e-t/rc= .... and then take natural logs of both sides. Then the e will dissapear and you'll end up with -t/rc = ......

Hope this helps!

Brian
 

BrianH

Joined Mar 21, 2007
43
If you need any further help, write down what your question is and I'll give you the solution with explanatory comments for each stage.

Brian
 

Papabravo

Joined Feb 24, 2006
13,539
Hello there.
....
e is a very special number which occurs in nature. It represents an exponential growth and is approximately equal to 2.135675x10-3.
...
Isn't the value of e about 2.718281828... give or take a bit? Where did you get your number?

The answer to the OP's question is that it comes from the solution to the differential equation for an RC circuit. Exponential functions to the base e have a very unique property, in that the function can be its own derivative.
 
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