Experimental Evaluation of RC Discharge Time Constants Across a Wide Capacitance Range: Evidence for Small Non-Ideal Resistive Effects

This study investigated how closely measured RC discharge time constants follow the theoretical relation τ = RC when capacitance is varied in a fixed-resistance circuit. Commercial capacitors from 0.068 μF to 1000 μF were discharged through an external resistor of 67.2 ± 0.1 kΩ, with three trials conducted for each capacitance. During each trial, the voltage across the capacitor was recorded using a PASCO voltage sensor, and the discharge curve was fitted to an exponential model to obtain the decay constant B; from which the experimental time constant was calculated as exp=1B. Mean experimental values were compared with theoretical predictions and were analysed using linear regression and a maximum-minimum gradient method to deduce uncertainty. The measured time constants increased linearly with capacitance and closely tracked theoretical values across the range investigated. A linear fit of exp against theory gave y = 1.0271x + 0.0127 with R² = 0.9981, indicating strong agreement with the ideal RC model but suggesting a small systematic deviation. Interpreting this deviation with an effective-resistance model gave an inferred additional series resistance of approximately 3 ± 3 kΩ. Overall, the findings support the validity of the ideal RC approximation while showing that non-ideal resistive effects are present but small.