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After one time constant, a charging capacitor holds about what fraction of its full charge?

About 63 percent, since 1 minus 1/e is 0.632.

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  1. About 37 percent
  2. About 63 percent ✔
  3. About 50 percent

Why: The time constant of an RC circuit is R times C. After one time constant, a charging capacitor reaches about 0.632 of its maximum charge.

Huh, didn't know that: When discharging, the charge falls to about 0.368 of its starting value after one time constant.

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References

Answer: About 63 percent. The time constant of an RC circuit is R times C. After one time constant, a charging capacitor reaches about 0.632 of its maximum charge.

  1. Physics LibreTexts (OpenStax University Physics II), 10.6 RC Circuits phys.libretexts.org/Bookshelves/University_Physics/University_Physics_(OpenStax)/University_Physics_II_-_Thermodynamics_Electricity_and_Magnetism_(OpenStax)/10%3A_Direct-Current_Circuits/10.06%3A_RC_Circuits
    charge equal to \(1 - e^{-1} = 1 - 0.368 = 0.632\) of the maximum charge
    Checked 2026-10-11.

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