RC Time Constant (Discharge τ = RC)

Discharge a capacitor through a known resistor. Record (t, V) and fit ln V versus time to get τ = RC.

School· 22 min·Related simulator: RC Circuit

Goal

From exponential discharge V = V₀ e^(−t/τ), use ln V = ln V₀ − t/τ; the slope of ln V vs t is −1/τ.

On discharge through R, dV/dt = −V/(RC) gives τ = RC. Linear regression of y = ln V against x = t has slope −1/τ, hence τ = −1/slope.

Connect the pre-set RC (simulated) and record voltage after closing the switch at t = 0.
Press “Record” at different times; small voltmeter noise is added.
Obtain at least 6 (t, V) points covering most of the decay.
The table shows ln V; run the linear fit vs t. Compare τ to the reference value.

Discharge model; set time, then record.

t (s)0.0020

№	Time t s	Voltage V V	ln V
No measurements yet — take your first reading.

Add at least 2 measurements to compute the fit.

Opens the system print dialog — choose “Save as PDF” or your printer. Header and footer are hidden when printing.

One click opens the print dialog — choose “Save as PDF”.

Generated: 27 Apr 2026, 02:36

From exponential discharge V = V₀ e^(−t/τ), use ln V = ln V₀ − t/τ; the slope of ln V vs t is −1/τ.

#	Time t (s)	Voltage V (V)	ln V
No measurements yet — take your first reading.

Add at least 2 measurements to compute the fit.

The recovered τ agrees with RC product within tolerance.

PhysSandbox virtual lab — values come from your session; add your own discussion of error sources.

The recovered τ agrees with RC product within tolerance.