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Registered Member #1822
Joined: Fri Nov 21 2008, 08:04PM
Location:
Posts: 300
My prof assigned some extra credit and the assignment is to find the missing resistance value. The circuit is an RC circuit with a 200uF cap and a 20V source. It charges the capacitor to 12volts in 30 seconds. Where would I start?
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
It's clear that -you- started by asking for help. For what kind of career are you studying RC circuits?
I would start by getting the formula for volts vs. seconds in "an RC circuit with a 200uF cap and a 20V source." Presumably that's regular subject material in your class and your textbook. Step 2: solve for R.
Registered Member #1822
Joined: Fri Nov 21 2008, 08:04PM
Location:
Posts: 300
Its not for a career in RC circuits, its just part of the class work. I looked through the current chapter and the next and all I found was the basic 63.2% per T. The value of R is somewhere near 150K which gives a voltage of 12.68V at the first 30 seconds.
search for "equation for capacitor discharging", and also remember it takes the same time to charge a capacitor from 0 to say 20% as it does to discharge from 100% to 80%
Registered Member #1667
Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 374
hint: solve the differential equation associated with this problem (why might the unit of charge be 1C= 1As?). You might as well waste the exercise and find the solution on the internet.
hint 2: Integration constants are not necessarily zero
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Capacitor Charging
