The complete discharge of a capacitor through a real resistor is limited by thermal noise. A meaningful discharge time td is defined by equating the charge across the capacitor in a noiseless RC circuit to the rms charge fluctuation in a noisy circuit Q0(td) =[〈 (δQ)2〉t]1/2. Three derivations are reviewed for the well‐known result 〈 (δQ)2〉t=kTC. One derivation shows explicitly that δQ (t) can be determined with the noise current in(t) as its source. Several examples of potential interest in the classroom are discussed.
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© 1979 American Association of Physics Teachers.
1979
American Association of Physics Teachers
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