Download ENT161LAB3 - UniMAP Portal

EXPERIMENT 3
Parallel Circuits & Voltage Divider Rules for Series Circuit
1.
OBJECTIVE:
1.1 To investigate the characteristics of a parallel circuit.
1.2 To examine the relationship between combinations of voltage drops and
combinations of resistance values in a series circuit using voltage divider rules.
2.
INTRODUCTION:
2.1 Parallel Circuits:
A Parallel circuit has certain characteristics and basic rules summarized here:
 A parallel circuit has two or more paths for current to flow through.
 Voltage is the same across each component of the parallel circuit.
 The sum of the currents through each path is equal to the total current that
flows from the source.
 You can find total resistance in a Parallel circuit with the following formula:
1/Rt = 1/R1 + 1/R2 + 1/R3 +...
Rt = R (total)
 If one of the parallel paths is broken, current will continue to flow in other
paths.
2.1.1
A parallel circuit has two or more paths for current to flow through.
This is self explanatory. Simply remember that PARALLEL means two
paths up to thousands of paths. The flow of electricity is divided
between each according to the resistance along each route.
Figure 3.1
Rule 1 for parallel circuit.
-24-
2.1.2
Voltage is the same across each component of the parallel circuit.
You may remember from the last section that the voltage drops across
a resistor in series. Not so with a parallel circuit. The voltage will be the
same anywhere in the circuit.
Figure 3.2
2.1.3
Rule 2 for parallel circuit.
The sum of the currents through each path is equal to the total
current that flows from the source.
If one path is drawing 1 amp and the other is drawing 1 amp then the
total is 2 amps at the source. If there are 4 branches in this same 2 amp
circuit, then one path may draw 1/4A (.25A), the next 1/4A (.25), the
next 1/2A (.5A) and the last 1A. Don't worry, the next rule will show you
how to figure this out. Simply remember for now that the branch
currents must tally to equal the source current.
Figure 3.3
Rule 3 for parallel circuit.
-25-
2.2 Voltage Divider
The voltage across one resistor equals the ratio of that resistor's value and the
sum of resistances times the voltage across the series combination. This
concept is so pervasive it has a name: voltage divider.
Referring to Single Loop circuit in Figure 3.4, which yields
Vin = Vout1 + Vout2,
where, Vout1 = R1i
Vout2 = R2i
Combining these equations, we find
And
Vin = R1i + R2i
i =
Figure 3.4
V / ( R1 + R2 ).
Single loop circuit
So finally the equations for voltage divider for both resistors are,
Vout1 =
R1
Vin
R1 + R2
Vout2 =
R2
Vin
R1 + R2
-26-
3.
COMPONENT AND EQUIPMENT:
3.1 Breadboard – 1 unit
3.2 DC power supply – 1 unit
3.3 Digital Multimeter – 1 unit
3.4 Wires
3.5 Resistors:
3.5.1 1.2 kΩ resistor - 1 pcs
3.5.2 1.8 kΩ resistor - 1 pcs
3.5.3 2.2 kΩ resistor - 1 pcs
3.5.4 3.3 kΩ resistor - 2 pcs
3.5.5 5.6 kΩ resistor - 1 pcs
3.5.6 33 kΩ resistor - 1 pcs
4.
PROCEDURE:
4.1 Parallel Circuit:
4.1.1
Part 1(a) - Voltage characteristic in a parallel circuit.
a)
Connect the circuit in Figure 3.5. Adjust the voltage source to a
value of 12 volts (with the circuit connected).
b)
Using the DMM, measure the voltage across each resistor.
Record your measurements in Table 5.1
Figure 3.5
Schematic diagram of circuits.
-27-
4.1.2
Part 1(b) - Current relationships in a parallel circuit.
a)
Connect the circuit in Figure 3.6. Make sure that the source
voltage is properly set to 12 volts with the circuit connected.
b)
Using a current meter, measure the current through each resistor
and the total current. Record your measurement in Table 5.1.
Figure 3.6
4.1.3
Schematic diagram of circuits.
Part 1(c) - Resistance relationship in a parallel circuit.
a)
Connect the circuit in Figure 3.7. Note that there is no source
voltage connected.
b)
Using a DMM, measure the total resistance. Record your
measurement in Table 3.1.
Figure 3.7
c)
Schematic diagram of circuits.
Remove each resistor from the circuit. Using the DMM,
individually measure R1, R2, and R3. Record your measurement.
-28-
4.2 Voltage Divider for Series Circuit.
4.2.1 Connect the circuit in Figure 3.8.
4.2.2
Measure and record below the voltage drop across each resistor. When
measuring VAB, the voltmeter probe should be connected to point A and
the common lead to point B. This would be expressed as VAB. Note that
in the subscript “AB”, the first letter “A” is the point to which the probe is
connected and the second letter “B” is the point to which the common
lead is connected. Therefore, the expression VAB means the voltage at
point “A” in respect to point “B”.
4.2.3
Properly label these measured voltage drops on each resistor in Figure
3.9. Mark the polarity (use a + and a - to indicate polarity) of the voltage
drop on each resistor.
4.2.4
Measure the voltage, VCE, between point C and point E. When
measuring, the voltmeter probe should be connected to point C and the
common lead to point E. This would be expressed as VCE. Note that in
the subscript “CE”, the first letter “C” is the point to which the probe is
connected and the second letter “E” is the point to which the common
lead is connected. Therefore, the expression VCE means the voltage at
point “C” in respect to point “E”. Record this voltage in Table 3.2.
4.2.5
In a like manner, measure and record the following in Table 3.2.
VAC =
VDG =
VCA =
(note opposite polarity!)
VEA =
VBF =
-29-
VCG = _______
Figure 3.9
Schematic diagram of circuits.
-30-
Name
:
______________________________
Matrix No
:
______________________________
5.
Date: ______________
RESULT:
EXPERIMENT 3: Parallel Circuits & Voltage Divider Rules for Series Circuit.
5.1 Information:
5.1.1
Always use the measured value of resistance for all calculations.
5.1.2
Always adjust the power supply voltage with the circuit connected.
5.1.3
When measuring voltage, the voltmeter must be connected across the
circuit element of interest.
5.1.4
When measuring current, the current meter must be inserted into the
“break” in the circuit (in series).
TABLE 3.1
15
TABLE 3.2
PROBLEM
(1)
PROBLEM
(2)
MARKS
10
10
50
15
%
Table 5.1 Voltage, current and resistance measured in Part 1
Part 1 (A)
Voltage (V)
Part 1 (B)
Current (mA)
Part 1 (C)
Resistance (ohm)
VR1 =
IR1 =
Rtotal =
VR2 =
IR2 =
R1 =
VR3 =
IR3 =
R2 =
Itotal =
R3 =
-31-
Name
:
______________________________
Matrix No
:
______________________________
Date: ______________
Table 3.2 Voltage measured in Part 2
Part 2
VR1 = VAB
VR2 = VBC
VR3 = VCD
VR4 = VDE
VR5 = VEF
VR6 = VFG
Voltage Measured (V)
VCE
VCA
VAC
VDG
VEA
VBF
VCG
-32-
Name
:
______________________________
Matrix No
:
______________________________
Date: ______________
6. EXERCISE:
6.1 Find the equivalent resistance seen by the source and current i.
-33-
Name
:
______________________________
Matrix No
:
______________________________
Date: ______________
6.2 In the voltage divider shown the power delivered by the source is 9mW and Vi =
V/4. Find R, V, Vi and i.
-34-
Name
:
______________________________
Matrix No
:
______________________________
7. DISCUSSION:
The current and voltage values is ..
8. CONCLUSION:
The conclusion for this lab is…
-35-
Date: ______________