Name : ______________
Class :
Group :____________
Page - 1 -
CCC4 : LRC circuit.
Objectives:
To use a datalogger CRO display to display the current and p.d. waveforms
To invetsigate phase relationship between current and p.d. in CR and LR circuits.
Apparatus :
Datalogger
LRC-circuit board
1
1
Voltage Sensor
connecting leads
2
Exp 1 :Study of C-R
(1)connect the voltage sensors to the interface and open the programme LCR.DS
(2) connect the circuit below .
(3) Connect the output voltage in a sine wave and Set the frequency of the output signal to 2 Hz and
2V peak voltage in the signal generator. Start the datalogger by clicking start.
fig 1
fig 2
8.2 mH
330µF
channel B
E
2V
channel A
10Ω
33Ω
100µ
100Ω
33Ω
330µF
E
output
E
Voltage Gain
Time Base
1
Name : ______________
Class :
Group :____________
Page - 2 -
4. Result and analysis
4.1 Draw the three CRO display curve , the Vr , Vc and Vcr (output voltage) in the fig 3 below.
Set the time base to 100ms/ div. You may freeze the pattern by stop the datalogger.
fig 3
The Phasor diagram of Vc , Vr and Vcr
Time base =
ms cm-1
4.2.Explain briefly why the Vc and Vcr are nearly in phase when the frequency is small ( 2 Hz).
______________________________________________________________________________
4.3 In fig 3, find the Phase difference between Vc and Vr. The phase difference between Vc and Vr is
_________
5 Increase the frequency of the output signal 40 Hz the signal generator.
6 Result and Analysis
Draw the three CRO display curves , the Vr , Vc and Vcr (output voltage) in the fig 4 below.for 40
Hz
The Phasor diagram of Vc , Vr and Vcr
fig 4
Time base =
ms cm-1
6.1 state the change of peak value of the Vr as the frequency increased(from 2Hz to 40Hz).
______________________________________________________________________________
6.2 Explain briefly why the Vr and Vcr are nearly in phase when the frequency is large ( 40 Hz).
______________________________________________________________________________
6.3 In fig 4, find the Phase difference between Vc and Vr. The phase difference between Vc and Vr is
_________.
2
Name : ______________
Class :
Group :____________
Page - 3 -
Smart Tool
6.4 Measure the peak value of the Vr. Using the smart tools. Then calculate the peak value of the
current Io and hence find the impedance of the CR circuit at 40 Hz.
Measure the peak value of the Vr. = __________ V
The peak value of the current Io = _____________= __________A
The impedance of the CR circuit at 40 Hz.=________________
3
Name : ______________
Class :
Group :____________
Page - 4 -
Exp 2 :Study of L-R
(1)connect the voltage sensors to the interface and open the programme LCR.DS
(2) connect the circuit below .
(3) Set the frequency of the output signal to 100 Hz in the signal generator. Start the datalogger by
clicking start.
fig 1
E
output
fig 2
8.2 mH
channel B
E
2V peak
10Ω
channel A
33Ω
100Ω
100µ
330µF
100Ω
E
(4)
4.1 Draw the three CRO display curve , the Vr , VL and VLr (output voltage) in the fig 3 below.
Set the time base to 2 ms.
fig 3
The Phasor diagram of VL , Vr and VLr
Time base =
ms cm-1
Answer the following question.
4.2 Explain briefly why the Vr and VLr are nearly in phase when the frequency is small (100 Hz).
______________________________________________________________________________
______________________________________________________________________________
4.3 In fig 3, find the Phase difference between VL and Vr. The phase difference between VL and Vr is
_________
5 Increase the frequency of the output signal in step of 100 Hz to 1000 Hz in the signal generator.
Start the datalogger by clicking start and display the waveform in a suitable timebase.
4
Name : ______________
Class :
Group :____________
Page - 5 -
6 Result and Analysis
6.1 Draw the three CRO display curves , the Vr , VL and VL r (output voltage) in the fig 4 below.
The Phasor diagram of VL , Vr and VLr
fig 4
Time base =
ms cm-1
6.3 State the change of peak value of the VL as the frequency increased.
______________________________________________________________________________
6.4 Explain briefly why the VL and VLR are nearly in phase when the frequency is large ( 1000 Hz).
______________________________________________________________________________
Exp. 3 LRC- In series Resonance
(1) connect the circuit below .
(2) Connect the output voltage in a sine wave and Set the frequency of the output signal to 10 Hz and
2V peak voltage in the signal generator. Start the datalogger by clicking start.
8.2 mH
channel B
330µF
10Ω
33Ω
100µ
100Ω
330µF
EB
2V peak
8.2 mH
channel A
10Ω
EA
E
output
(4) Measure the peak value of the Vr at different frequencies from 10 to 160 Hz
5
Name : ______________
Class :
(5) Results and analysis
frequency /Hz 10 20 30
Vr / V
Group :____________
50
60
70
80
90
Page - 6 -
100 110 120 130 140 160
5.1 find the frequency fo at which , the peak value of Vr is maximum in a step of 1Hz.The frequency
fo is called the resonance frequency.
fo = _______ Hz and the Vr at resonance = ______V
5.2Explain briefly why the p.d. across R is not equal to the output voltage (i.e. 2V)
______________________________________________________________________________
______________________________________________________________________________
5.3 Sketch the variation of peak value of Vr with frequency.
5.3 State three precautions in doing Exp1 and Exp 2.
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
6
Name : ______________
Class :
Group :____________
Page - 7 -
5.4 Sketch the waveform display in Datastudio Scope display of VLCR , Vr and Vc at the frequency
of fo.
The Phasor diagram of VL ,Vc, Vr and VLCR
fig 4
Display analysis
At resonance:
(1) Io is maximum and impedance of LCR is __________________ and is equal to _____
(2) VL and Vc are in ________ ( anti-phase / phase) and VL = Vc.
Therefore VLC = ____ although VL and Vc are in a __________ ( large or small ) value.
(3) VLCR
and VR
are in __________ ( phase/out of phase / anti-phase ) and Value of VR = VLCR.
7