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Re: RC circuits lab



I didn't read oscilloscope in any of the replies! If you use one, as mentioned in some, one must use a low enuff Z so the 'scope doesn't load the circuit. A 10X probe (therefore, usually 10 meg Ohms) will allow more flexibility. Finally add a gas tube, and you'll have a relaxation
oscillator! With an Ne-2, 100 k Ohm, 1 micro Fd, and a 100 V supply, you'll have very approximately ten Hz. Scope across the 100 K the charging current, across the cap. the voltage.

bc

P.s. Time constant (one over "e") in seconds is micro farads times megohms, so the above has one tenth sec. Cap, of course, paper, mylar, polystyrene, etc. Ready to go is a disposable camera. Direct connection to the circuit is probably OK -- max. voltage is ~ 300 V. and the charging R is
the internal resistance of the supply. It probably varies so may be an added "wrinkle." The exercise is to determine its R. Add R to find the capacitance and to use for measuring the current.

P.p.s. Apology: A few of you did suggest CBL or MBL -- the inexpensive 'scope.

Justin Parke wrote:

Can someone refer me to a good lab I can do with Advanced Placement (C) physics students for RC circuits? I want them to measure current and voltage several times as a capacitor charges/discharges and obtain the exponential curves which we can then fit and derive the proper equations.

My main problem is my lack of experience with these type of circuits so that I do not know which combinations of resistance, capacitance, and applied voltage provide the proper charging time, etc. I blew up a capacitor the other day while I was playing in the lab (and supplies are limited!)

Perhaps some of you have written something of your own you could share with me, or refer me to some website.

Thanks

Justin Parke
Oakland Mills High School