Physics Experiment 9 Stpm Sem 2 Apr 2026

A capacitor stores electrical energy in an electric field. When a charged capacitor discharges through a resistor, the potential difference ( V ) across the capacitor does not drop instantly to zero. Instead, it follows an exponential decay described by the equation:

Here, ( V_0 ) is the initial voltage, ( R ) is resistance, ( C ) is capacitance, and ( t ) is time. The product ( RC ) is known as the , representing the time required for the voltage to fall to approximately 36.8% of its initial value. In this experiment, students verify this relationship by measuring voltage at regular time intervals and plotting a semi-logarithmic graph to extract τ. This experiment reinforces Kirchhoff’s laws and introduces the concept of transient behavior—crucial for understanding filters, timing circuits, and signal processing. physics experiment 9 stpm sem 2

[ V(t) = V_0 e^{-t/RC} ]

A well-conducted experiment yields a linear plot of ( \ln(V) ) vs. ( t ), confirming the exponential decay model. For instance, if the slope is found to be -0.095 s⁻¹, then ( τ = 1/0.095 ≈ 10.5 ) seconds. Comparing this experimental time constant with the theoretical value ( RC ) (e.g., 10 kΩ × 1000 µF = 10.0 s) gives a percentage error typically within 5–10%, depending on component tolerances and reaction time errors. Sources of discrepancy include the internal resistance of the voltmeter, leakage in the capacitor, and human latency in starting/stopping the stopwatch. A capacitor stores electrical energy in an electric field

Moreover, this experiment has real-world applications. Understanding RC time constants is fundamental to designing pacemaker timing circuits, camera flash units, and debouncing switches in digital electronics. In research, similar methods are used to characterize dielectric materials and measure unknown capacitances or resistances. The product ( RC ) is known as