Download Cell`s Connection.

POLYTECHNIC OF KOTA BAHRU
DEPARTMENT OF ELECTRICAL ENGINEERING
ET101 – ELECTRICAL TECHNOLOGY
EXPERIMENT 1
TOPIC
:
OBJECTIVES :
At the
i.
ii.
iii.
iv.
v.
vi.
CELL’S CONNECTION
end of this experiment, students should be able to :
Use the power supply unit correctly.
Measure the voltage of cells in series.
Measure the current that flow in the series circuit .
Measure the voltage across the load resistor using the voltmeter correctly
Understand the theory of cell’s connection.
Determine the relation between voltage and current in a circuit
THEORY
Cell’s Connection.
The electromotive force (e.m.f), E , of a cell is the p.d. between its terminals when it is not
connected to load. The e.m.f of cell is measured by using a high resistance voltmeter connected
in parallel with the cell. The voltmeter must have a high resistance.
The voltage available at the terminals of a cell falls when a load is connected. This is caused by
an internal resistance of the cell which is the opposition of the material of the cell to the flow
of the current. The internal resistance acts in series with other resistances in the circuit. FIG.1
shows a cell of e.m.f E volts and internal resistance, r , and XY represents the terminal of the
cell.
r
E
V
R
When o load R is not connected, no current flows and terminal p.d. , V = E .
When R is connected acurrent I flows which causes a voltage drop in the cell, given by Ir . The
p.d available at the cell terminals is less than the e.m.f. of the cell and is given by ;
V = E - Ir
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POLYTECHNIC OF KOTA BAHRU
DEPARTMENT OF ELECTRICAL ENGINEERING
ET101 – ELECTRICAL TECHNOLOGY
A battery is a combination of more than one cell. The cells in the battery may be connected in
series or in parallel.
(i) For cells connected in series :
Total e.m.f = sum of cell’s e.m.f.’s.
Total internal resistance = sum of cell’s internal resistances.
(ii) For cells connected in parallel:
If each cell has the same e.m.f and internal resistance;
Total e.m.f = e.m.f of one cell.
Total internal resistance of n cells = 1/n x internal resistance of one cell.
EQUIPMENTS :
i.
ii.
iii.
iv.
v.
vi.
vii.
Variable resistor
Ammeter
Voltmeter
Multimeter
Power Supply Unit
Cable
Cells
PROCEDURES :
1.
2.
3.
The four cells you will use in this experiment should have the same voltage. Measure the
voltage of each cell and record the value in Table 1.
Connect the three cells as in Figure 4.1. Measure the voltage across the combination of three
cells and across the combination of cells 1 and 2, across 2 and 3. Record the values in
Table 1 .
Reverse cell 1, as shown in Figure 4.2. Measure the voltage across the combination of
three cells and across the combination of cells 1 and 2, and across 2 and 3. Record the
value in Table 2.
Cell 1
+
Cell 2
+
Cell 3
+
Figure 4.1.
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POLYTECHNIC OF KOTA BAHRU
DEPARTMENT OF ELECTRICAL ENGINEERING
ET101 – ELECTRICAL TECHNOLOGY
+
Cell 1
-
-
Cell 2
+
Cell 3
+
Figure 4.2
4.
Connect the circuit as shown in Figure 4.7 below. The cells are connected series-aiding..
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POLYTECHNIC OF KOTA BAHRU
DEPARTMENT OF ELECTRICAL ENGINEERING
ET101 – ELECTRICAL TECHNOLOGY
5.
6.
Measure the voltage across R1, and individual voltages across cell 1 and 2. Record the
value in Table 3 .
Measure the current in the circuit as in Figure 4.8 and record the value in Table 3.
7.
Reverse cells as shown in Figure 4.8.
8.
Do this step quickly. Connect the meters with the polarities as indicated. If analog meters
are used, note if the pointer moves off scale to the left. Reverse the meter leads and
record any values as minus. If a digital meter is used record any negative readings.
( Do not allow shorting links between sockets 2 .3 & 2.4
for any length of time – make
your measurements quickly and disconnect the shorted links )
9.
By referring to the Figure 4.7 and 4.8 . Measure the current in the circuit
and voltage
across R1 and the individual voltage across cell 1 and cell 2. Record the values in Table 3.
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POLYTECHNIC OF KOTA BAHRU
DEPARTMENT OF ELECTRICAL ENGINEERING
ET101 – ELECTRICAL TECHNOLOGY
RESULT :
Nominal Cell
Voltage, V
Cell Number
Measured Cell
Voltage,V
Calculated Cell
voltage, V
1
2
3
1, 2, 3
1, 2
2, 3
Table 1: Cells Series Connected Aiding
Cell Combination
Measured Voltage, V
Calculated Voltage, V
1, 2, 3
1, 2
2, 3
Table 2 :Cells Series-Connected Opposing
Series-aiding Cell
Voltage, V
Circuit Element
Series-opposing cell
Voltage, V
Resistor R1
Cell 1
Cell 2
Current (A)
I=
I=
Table 3 : Series Cells in Circuit
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POLYTECHNIC OF KOTA BAHRU
DEPARTMENT OF ELECTRICAL ENGINEERING
ET101 – ELECTRICAL TECHNOLOGY
DISCUSSION ;
1.
Discuss about the voltage and current when the cells are connected in series.
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CONCLUSION :
Give your conclusion from the experiment.
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