Lab 4:

Capacitors and RC Circuits

Daisy Henderson

Introduction:

The purpose of this lab was to gain a deeper understanding of capacitors and to understand different wave patterns of an RC circuit. The formula = RC can be used to determine the values resistors and capacitors for certain time constants.

A capacitor is used to hold a charge and has a certain charging and discharging that can be seen on an oscilloscope when a charge is applied throughout the circuit.

Procedure:

First, a capacitor and resistor were chosen to create a circuit that had a time constant of 1 millisecond. The function generator was then turned on and set to 50 Hz with an amplitude of 2V, then it was connected to the oscilloscope and set to a square signal, the resulting wave was then recorded. The function generator was then connected to the RC circuit, and the signal across the capacitor was displayed on the oscilloscope and the results were recorded.

For the second circuit, the same capacitor was used along with two 50 ohm resistors in parallel and one 100 ohm resistor in series. A 1 KHz square signal was then applied to the circuit. The oscilloscope then was connected to the capacitor and the wave was recorded.

Results:

= RC

1 millisecond = 100 KΩ (resistor)* 1 mF (capacitor)

Measured Period = 20 milliseconds

Conclusion:

Based on the frequency in the first part of the lab, it was calculated that the period would be 4 millisecond, based on Hz = 1/period. This matches perfectly with the measured period from the oscilloscope. When the voltage was applied to the capacitor it was observed that the signal was distorted, and was not perfectly square, this is due to the fact that the capacitor was charging, and then releasing charge, causing the distorted shapes. It was also seen that the time it took the capacitor to charge was roughly 4 milliseconds. To determine the highest time constant to maintain the 1 Khz signal, it was calculated and found that the time constant would be .125 milliseconds. Finally, it was determined that the higher the frequency was that was applied to the circuit, the less steep the waves appeared on the oscilloscope.