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EXPERIMENT-3
POWER IN DC CIRCUITS
BAŞKENT UNIVERSITY
BIOMEDICAL ENGINEERING DEPARTMENT
BME 211 CIRCUIT THEORY-I LAB.
EXPERIMENT 3 POWER IN DC CIRCUITS
Objective
1) To investigate the internal resistance of voltage sources.
2) To use variable resistors in applications.
3) Using delta-to-wye transformation to simplify circuits.
1. INTRODUCTION
Measuring the internal resistance of voltage sources
If a load R is connected to a voltage source, the output voltage generally falls. The reason
for this is the internal resistance Ri of the voltage source which is connected in series with
the external load.
Voltage Source
U0
Ri
+
U
R
If the unloaded voltage source possesses
the open-circuit voltage U0, the voltage
U at the terminal of the loaded voltage
source is
U=U0 - Ri*I
Fig.1
In the event of a short-circuits, i. E. U = 0, the total voltage thus already drops across the
internal resistance.
Variable Resistor (Potentiometer)
A 3 pinned variable resistor is like next figures, made of a
carbon strip and a slipping pin. So if you have an “A”
ohm variable resitor you have two different resistor
between A-C and these resistor’s values are in range
between 0-A ohm.
Example:
A=10 kohm
R(A-B)=3 kohm => R(B-C)=A-3 = 7 kohm
Fig.2
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EXPERIMENT-3
POWER IN DC CIRCUITS
2. PRELIMINARY WORK
Fig.3
2.1 If you want to take IS=2 mA from power supply, find the “x” value of variable
resistor.(There is a 3 pinned variable resistor in the box.)
Fig.4
2.2 Read Delta-to-Wye equıvalent circuits chapter in your text books. Find the IS value in
Fig-4. ( Hint: Use - transformation )
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EXPERIMENT-3
POWER IN DC CIRCUITS
3. EXPERIMENTAL WORK
2.2
kohm
4.7kohm
Fig.5
3.1 Set up the circuit in the figure 4.Find the “x” value of the variable resistor to take 2 mA
from supply.(Hint: Connect an ampermeter to supply in series and change variable resistor
to obtain 2 mA on the ampermeter. ) Write your x value.
Rg
Fig.6
3.2 Set up the circuit in figure 6. Measure necessary V L and IL values and calculate PL
values for different RL values. Put a variable resistor with a range between 0-20 kohm for
RL. (Hint: convert a 3 pinned variable resitor to 2 pinned variable resitor by connecting
inner pin to one of outer pins.) Draw a PL-RL graph.
3.3 Find the inner resistance of the voltage source. Note the load resistance in your report..
4. RESULTS AND CONCLUSION
4.1 What is the relation between Rg and RL ,which maximize the PL, in experiment 3.2
4.2 Where can you use the concept that you found in 4.1.
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EXPERIMENT-3
POWER IN DC CIRCUITS
Name
:
Lastname :
Student id :
Set No
:
Name
:
Lastname :
Student id :
Set No
:
5. REPORT
3.1
x=
3.2
RL()
5000
6000
7000
8000
9000
10000
11000
12000
13000
14000
15000
VL
IL
PL
Graph:
3.3
Rin =
4.1
4.2
4