OBSERVATION: - Renaldo was putting a set of lights on the Christmas tree. The set was composed of 3 chains of lights in parallel. When one chain of lights blew, the other chains seemed to light as brightly as before (showing that the current in each chain remained the same).
AIM: - To determine the effect of number of lamps in parallel on the c urrent in each branch and the total current of the circuit.
APPARATUS & MATERIALS: - Three identical bulbs and bases, three cells and holders, connecting wires, four ammeters, three switches, voltmeter.
VARIABLES: Manipulated variable: - Number of branches.
Controlled variable: - Voltage of the cells.
Responding variable: - Current in the branches + circuit.
DIAGRAM: -
METHOD: 1).The circuit was set up as shown in the diagram above using a single cell.
2).The current (I) in each parallel branch and also the total current (I T) flowing through the circuit were measured using the various ammeters.
3).The values of voltage (V) were obtained from the voltmeter connected between the two junctions of the parallel branches.
4). One parallel branch was left connected to the circuit by opening the switches in the two remaining branches.
5).The readings of current in each parallel branch together with the total current flowing through the circuit were then measured.
6). Two parallel branches were now connected to the circuit by opening the switch in a branch, the current flowing through these branches together with the total current flowing through the circuit were then measured.
7).Each switch in this parallel arrangement was closed and the readings of current in each branch as well as the total current flowing through the circuit were measured.
8). A second cell was after added to the setup and the above steps carried out were completed.
9). A third cell was then added to the setup and the above steps carried out were completed.
10).The results of the experiment were tabulated in the table shown below.
11).Graphs of branch current versus number of branches, Total current versus number of branches, and potential difference across branches versus number of branches were then plotted.
12).Any trends observed from the plot of these graphs were after noted to raise possible suggestions that would answer the aim of the investigation.
RESULTS: -
TABLE SHOWING THE RESULTS OF THE EXPERIMENT Number of cells
Branch Number
Voltage
A1
A2
A3
AT
Number of open branches
1
1
1.4
0.14
0.00
0.00
0.15
2
1
2
1.4
0.14
0.12
0.00
0.25
1
1
3
1.4
0.15
0.12
0.12
0.38
0
2
1
2.6
0.22
0.00
0.00
0.22
2
2
2
2.6
0.20
0.18
0.00
0.37
1
2
3
2.6
0.20
0.16
0.14
0.50
0
3
1
4.0
0.26
0.00
0.00
0.25
2
3
2
3.8
0.24
0.22
0.00
0.45
1
3
3
2.6
0.23
0.21
0.22
0.65
0
DISCUSSION: A parallel circuit is one with several different paths for the electricity to travel. It’s li ke a river that has been divided up into smaller streams, however, all the streams come back to the same point to form the river once again. In this arrangement, the loads are parallel to each other. If the loads in this circuit were light bulbs and one blew out, there is still current flowing to the others because they are still in a direct path from the negative to positive terminals of the battery. The current in a parallel circuit is divided among the branches of the circuit. How it is divided depends on the resistance of each branch. Since the current divides, the current from the source is equal to the sum of the currents through each of the branches. The voltage of the battery is the same as the voltage drop across each resistance in the circuit. Therefore, several different loads requiring the same voltage may be connected in parallel.
The experiment was carried out to investigate the effect of number of lamps in parallel on the current in each branch and the total current of the circuit. This was done by setting up an electrical circuit as shown in the diagram above. The number of cells, together with the number of open and closed branches were varied and the various data for current (I) together with voltage (V) were obtained. Graphs representing these data were then plotted and utilized to identify likely trends that could have provided appropriate ideas to answer the aim of the investigation. From the results collected a variety of trends were observed: Firstly the total current flowing through each parallel branch was changed slightly when the number of active branches was varied. Since the bulbs used in this experiment were roughly of the same resistances but not exactly equal, the current flowing through them adjusted in such a way that the product of R and I remained the same i.e. Voltage remains constant. The flow of current across any branch is dependent on the value of resistance of that branch of the network. If the resistance is high the current will be low and vice versa. This shows why the total current flowing through each parallel branch changed slightly when the number of active branches was varied and an observable pattern of this trend is seen on the graph of branch current versus number of branches.
This high low trade off between resistance and current is done only by keeping their product constant i.e. V= constant in parallel. In order to keep the potential difference of the cells constant, this experiment required the use of special equipment. With the equipment utilized, it was very difficult to keep the voltage under control. As more branches were added to the circuit the terminal potential difference of the cells began to change, however there was no way of keeping this property of the setup constant with the apparatus used. The relationship between voltage, current, and resistance is described by Ohm’s law. This equation I=V/R tells us that current, I, flowing through a circuit is directly proportional to the voltage, V, and inversely proportional to the resistance, R. In other words, if we increase the voltage, the current will also increase provided the resistance of the circuit does not change. As a result of this fac t the terminal potential difference of the cells began decreasing from the addition of more loads to the circuit, due to their being an increased amount of resistance. This caused the current in each branch to fall, and may have compromised the quality of analysis as to whether the number of branches affects total current and current per branch. These effects can also be used to explain why the graph of potential difference against number of branches had decreasing gradients.
Another trend observed throughout the investigation was that the total current (I T) flowing through the circuit began to increase when the number of parallel branches were increased. As the number of branches added to a parallel circuit increases, the total resistance decreases. Total current that flows from the power source is inversely proportional to resistance, and according to theory should be proportional to the number of branches (R EFFECTIVE is inversely proportional to the number of branches). The term inversely means that if one value changes, the other value changes in the opposite way. This means that an increase in the number of parallel branches which causes the total resistance (RT) to decrease would have in fact resulted in the total current flowing through the circuit actually increasing. This increase in total current flowing through the circuit was also observed from the results of the investigation.
As stated earlier, the addition of more loads to the circuit resulted in a c hange (drop) of the terminal potential difference of the cells. This could be a likely source of error in the investigation and a means to improve the overall experiment. This is so as if more accurate potential difference control mechanisms were put in place for example by utilizing a variable resistance (rheostat) to keep the voltage constant. We would have been able to accurately observe the pattern in the experiment, which was that as the overall resistance halves the current doubles and so on.
It was also said above that the current (I) in each of the branches were not exactly the same. This could be explained by the fact that the manufacturing process makes lamps that have approximately the same resistance but the resistances are not exactly but roughly equal. Hence the total current flowing through each of these branches varied slightly as the bulbs were not all of equivalent resistances.
PRECAUTIONS: 1). It was ensured that all readings on the ammeters were taken at eye level so as to avoid parallax errors.
2). It was ensured that identical bulbs (of almost equal resistances) were used throughout the experiment.
SOURCES OF ERROR: 1). As a result of the manufacturing process the current In each of the parallel branches varied slightly as the bulbs were not all of equivalent resistances.
2).The lack of proper potential difference control apparatus for example a rheostat might have caused the potential difference of the cells to the vary.
REFLECTION: The investigation has provided me with a better understanding of parallel circuits and how they work. A good real life example where knowledge of parallel circuits may be critical is in house wiring. In a house, there are many electrical appliances that have to run independent of each other. If one appliance is turned on or off it should not af fect the other appliances. This is not possible if all the appliances were connected in a series arrangement as there would be one switch that either switches all of them on or off. When appliances are connected in a parallel arrangement, each of them can be put on and off independently. This is a feature that is essential in a house’s wiring. Also, if the appliances were wired in series, the potential difference across each appliance would vary depending on the resistance of the appliance. This would make it very difficult to provide the right power to flow through the appliances. When house wiring is done in parallel this problem does not arise as the potential difference across each appliance is the same and equal to the potential difference being provided by the power company. Thus knowledge of parallel circuits is not only useful for lab demonstrations but al so too everyday examples as well.
CONCLUSION: - Within the limits of experimental error an investigation was conducted to determine the effect of number of lamps in parallel on the current in each branch and the total current of the circuit. From the data collected and the trends observed from the graphs plotted it was found that the current flowing through each parallel branch changed slightly when the number of active branches were varied, and the total current flowing through the circuit increased when the number of parallel branches were increased.
