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Calculating time constant in RC Circuit 
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#1
Feb2508, 05:29 PM

P: 58

1. The problem statement, all variables and given/known data
You see this trace on your oscilloscope for an RC circuit. The vertical scale is 5volt/square and the horizontal scale is 50ms/square. What is the time constant of the RC circuit? 2. Relevant equations Vc(t) = Vo(e^(t/RC) Vr(t) = Vo * e^(t/RC) t halftime = Tln(2) = .69T 3. The attempt at a solution So when the voltage is at its peak (15 V), that's Vo. and if I take that as V(t), it's V at 20 ms (approximately). Substituting this: 15 V = 15V(e^(.02/RC)) 1 = e^.02/RC ln(1) = .02/RC 0 = .02/RC Cross multiplying to solve here doesn't help me. Is there another formula I can use? 


#2
Feb2508, 05:39 PM

P: 329

[tex] 13 = 15 e^{0.02 s/RC} [/tex] 


#3
Feb2508, 08:13 PM

P: 58

Yeah, that's what I did..I said that the V at 20 ms was 15 (the peak). Should I just pick another arbitrary time?



#4
Feb2608, 08:43 AM

P: 329

Calculating time constant in RC Circuit
V_0 is the voltage at t=0 I think your mistake is that you did not reset t=0 at the point where the decreasing exponential starts. If you measure V_0 at the peak, you must set t=0 at that point. 


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