Please find here the answers for the StudentZone article June 2018.
Question 1:
Using equations (5) and (6) determine the impedance (Zcircuit) and phase (θ) relationship of the current relative to the voltage for a RC circuit by replacing the A and B variables with proper values.
Answer 1:
We consider the following equations for RC circuit:
- impedance:
- phase relationship of the current relative to the voltage:
The impedance of the capacitor is: 
The impedance of the resistor is: 
Therefore, we can compute the circuit impedance as follows:
And phase: 
Where: 
is known as the capacitive reactance of the capacitor.
Question 2:
For RC circuit in Figure 6, measure the time difference and calculate the phase θ offset at 1000 Hz frequency.
Answer 2:
Taking into consideration the setup made for the RC circuit measurements, additional steps must be followed:
- Set AWG CHA to 1000 Hz and the time / div to 0.2 msec/div.
- Put a first marker at the neg. to pos. zero crossing location for the CA-V ( VR1+ VC1) signal. Put a second marker at the nearest neg. to pos. zero crossing location for the Math ( VR1 ) signal. Record the time difference (∆t) and calculate the phase angle(θ). Note ∆t maybe a negative number. Does this mean the phase angle leads or lags?
To remove the markers for the next measurement click on the red Stop button.
- Put a first marker at the neg. to pos. zero crossing location for the CA-V ( VR1+ VC1) signal. Put a second marker at the nearest neg. to pos. zero crossing location for the CB-V ( VC1 ) signal. Record the time difference (∆t) and calculate the phase angle (θ).
- Put a first marker at the neg. to pos. zero crossing location for the Math ( VR1) signal. Put a second marker at the nearest neg. to pos. zero crossing location for the CB-V ( VC1 ) signal. Record the time difference and calculate the phase angle.