# Transient Response of RC circuits

# Objective

Plot the voltage across a capacitor, when it is charged by applying a voltage step through a resistor. Extract the value of RC from the graph by curve fitting.h.

# Procedure

- Make connections as shown in the figure
- Click on 0->5V STEP and 5->0V step Buttons to plot the graphs
- Adjust the horizontal scale, if required, and repeat.
- Calculate RC time constant.

# Discussion

Applying a 0 to 5V step makes the voltage across the capacitor to rise exponentially as shown in the figure. By fitting the discharge curve with V(t) =V0×e−t⁄RC, we can extract the RC time constant and find the values of capacitance from it.

The voltage across a capacitor is exponential only when it is charged trough a linear element, a resistor for example. When charged from a constant current source, the voltage shows linear increase, because Q=It=CV , and voltage increases linearly with time as V= (I⁄C) ×t.

Is it necessary to have the voltage across the capacitor be exponential during charging ? Try the following configuration