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
---------

.. image:: schematics/RCtransient.svg
	   :width: 300px

-  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.

.. image:: pics/RCtransient-screen.png
	   :width: 400px

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 :math:`V(t) = V_0 \times 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
:math:`Q = It = CV` , and voltage increases linearly with time as
:math:`V = (I/C) \times t`.

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

.. image:: schematics/cap-lin.svg
	   :width: 300px
