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PRACTICE · MEMBERSIntermediate · Single correct

PRACTICE / RC transients

Half the voltage, one quarter of the energy

A charged capacitor discharges through a resistor with time constant τ = 0.40 s.

When does its stored energy first become one quarter of its initial energy?

Organize the givens & assumptions
  • Time constant: 0.40 s
  • Final energy fraction: 1/4
  • No external source during discharge

Ideal discharge with no source and constant R and C. The capacitor begins with nonzero voltage.

  1. A0.40 s0.40\ \mathrm s
  2. B0.20 s0.20\ \mathrm s
  3. C0.40ln⁡2 s0.40\ln2\ \mathrm s
  4. D0.40ln⁡4 s0.40\ln4\ \mathrm s

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