- #1
Jonas E
- 15
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Homework Statement
I have an RC circuit where C = 0.4 * 10^-6, R = 50k Ohms. The problem says: "Find the length of time required to dissipate 75% of the initially stored energy."
Homework Equations
energy 1: 1/2 * C * v(t)energy 2) w = ∫p(t)dx, from 0 to t
The Attempt at a Solution
This is the last part of the problem. I solved everything else up to this point correctly. v(0) = 200 V, Tau = 0.02s. The initial energy stored in the capacitor is 8mJ. Now I set p(t) = v(t) / R, and integrate from 0 to t. That gives me the expression for the energy, which I then set equal to 0.25 * w(0) = 2 * 10^-3 J. However this gives me that t = 2.877ms, which is wrong according to the solutions manual. It uses the first energy formula and gets t = 13.86ms. Can someone explain why these two formulas give two different answers, or point out any mistake I have done.