AC Signal #1

In the lab, the purpose is to explore the phase difference between AC sine signals at the same frequency in a simple RC circuit; besides, by adjust the frequency of the signal and resistance in the circuit, the phases will be different. Also, we can learn how to read the value of current or voltage on the scope display.

The measurement of phase difference is time difference between the positive peaks multi by the frequency and 360. In this scope display, since CH1 takes its peak before the CH2 signal, we say that the CH1 signal leads the CH2 signal.

Set the FG to produce 1 V peak-peak sine wave at 1k Hz. The RMS value for DMM is 0.318 V. The complex impedance of the 100 nF capacitor can be calculated as 1/(2*pi*C) = 1592 ohms. Next, we connect CH1 to FG and CH2 to the top of capacitor, and then Resistor box and C connected as shown above.

DATA:

CH2 Vcap, pk-pk  = 0.852 V

CH2 Vcap, rms  = 0.23 V

tx =105.41 us

According to the method mentioned before

phase change = tx * f * 360 = 37.9 degrees

CH1 is leading CH2 by 37.9 degrees

Next adjust the frequency of input signal to 10 kHz rather than 1k Hz.

CH2 Vcap, pk-pk =0.154V

CH2 Vcap, rms = 0.033 V

tx=23.78 us

phase change = tx * f * 360 = 85.6 degrees

Adjust the resistor box to 10 Kohms.

CH2 Vcap, pk-pk = 0.178 V

CH2 Vcap,rms = 0.049 V

tx = 221.62 us

Phase change= tx * f * 360 = 79.8 degrees

LOW frequency range is the capacitor voltage amplitude greatest.

HIGH frequency range is the capacitor voltage amplitude smallest.

If a filter is a device that selectively passes through a certain range of f, the circuit is being LOW PASS