physics resistor?

Question

Problem 31.41
What value resistor will discharge a 2.70 microFarads capacitor to 20.0 % of its initial charge in 2.10 ms? Answer in ohms

Answer 1

The time function of voltage will be
v(t)=V0*(1-e^(-t/T) T=R*C
when v(t)=.2*V0 at 2.1 ms
.8=e^(-2.1/T)

R=2.1x10^-3/(LN(1/.8)*2.7x10^-6)
R=3.5 kOhm

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