How to turn your physics book into a capacitor!
A page by Devin Boyer

The Theory - The Finished Product - The Tools, The Plan - Parallel Circuits - Series Circuits - Bibliography

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Series Circuits

The second experiment involves putting the capacitor between the two ohm-rangers. This is a series circuit, much like the voltage divider from the parallel page. However, the capacitor significantly changes the output. As the capacitor charges to the maximum voltage (either 7.5V or -7.5V), the current flowing through either resistor slows down to a trickle. Because the resistors are 1k ohm, it is easy to calculate the current flow through the resistor; one mA of current flows for each volt across it. In the case of the second resistor, towards the end of each cycle, the voltage drops to zero. This indicates that the capacitor is fully charged and acting like an open. When a transition occurs, the current once again flows as it charges the capacitor in the other direction.


Series RC circuit


Series RC circuit


Oscilloscope output of series RC circuit

For experiment's sake, the signal generator was set to put out sine waves. Because the signal is always changing, the capacitor never charges to a nominal level, and the output always shifts as a result. Because of the capacitance, however, the output (channel one) lags the output (channel 2) by a little bit. This speaks much about capacitors usage: by selecting a particular capacitance, it is possible to filter out DC signals, but pass AC signals relatively unchanged.


Series RC circuit driven with a sine wave