(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A 50 uF(microfarad) capacitor that had been charged to 30 V is discharged through a resistor. Figure 31.73 (attachment) shows the capacitor voltage as a function of time. What is the value of the resistance?

2. Relevant equations

Q = Qo e^(-t/RC), o = initial

Qo = CV, o = initial

I = Io e^(-t/RC), o = initial

3. The attempt at a solution

Original V = 30, the final V at 3ms is approximately 7V. Thus the final charge is 0.233 (7/30) of the initial charge.

Q = Qo e^(-t/RC)

ln (7/30) = -3/(R)(50 uF)

R = 0.041 ohms

The right answer is 36.4 ohms.

Any suggestions?

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# Resistance from a V-time graph

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