The aim of this experiment is to investigate the relationship between the current, voltage and resistance through the use of a fixed resistor and a filament lamp.
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Aim The aim of this experiment is to investigate the relationship between the current, voltage and resistance through the use of a fixed resistor and a filament lamp. Hypothesis Based on knowledge of Ohm's law it can be hypothesised that when increasing voltage and current is passed through a filament lamp the resistance would increase in a non-linear fashion, such that a graph similar to the one given below would be obtained (figure 1). This non-linear graph would be expected due to temperature increases in the filament lamp. It can also be hypothesised that when current is passed through a fixed resistor the relationship between V and I would be expected to be linear such that a straight line through the origin would be obtained (figure 2). In addition the readings on the ammeter and voltmeter would both change accordingly as expected. The shape of a fixed resistor current-voltage graph (I-V graph) is explained in figure 3 since the three variables are related through Ohm's law. Circuit Diagrams Equipment Fixed resistor & Filament Lamp- to impede and obstruct current flowing through circuit Ammeter- to measure current flowing through the circuit Voltmeter- to measure the voltage present in the circuit and to make sure the power supply is correctly calibrated. Power Supply- to act as the adjustable power source for the circuit Wires- to connect the circuit components. Tangles were removed from the wires as not doing so could result in erroneous values being obtained in experiment, as using several different wires or tangled wires during the experiment could lead to varied resistance and poor fair test (Figure 6).
The PSU was set to zero volts and the circuit was turned back on after making sure that the filament lamp was in tact. The voltage readings were then repeated as before and were inserted in another table and averaged out. Following this the equipment was cleared away after making sure that hands were dry. The tables were then plotted onto graphs. Method in summary: 1. Apply safety precautions. 2. Gather equipment and connect it according to figure 4. 3. Recheck for safety and turn the circuit on. 4. Increase the Voltage by 2V every reading and note the current reading on the ammeter. 5. Once 12V is reached switch the PSU off. 6. Replace resistor with a Filament Lamp 7. Carry out steps 3-5 again. 8. Once readings for filament lamp and fixed resistor are tabulated clear up equipment. 9. Plot an I-V graph for the fixed resistor and Filament Lamp. Variables The controlled variable in this experiment is the Equipment used The input variable in this experiment is the voltage. The output variables of this experiment are the current and resistance. Tables of results Table 1 Circuit with fixed resistor Voltage (V) Current (A) 0.00 2.10 4.10 6.20 7.90 10.00 12.10 0.00 0.20 0.44 0.58 0.71 0.92 1.10 Table 2 Circuit with filament lamp Voltage (V) Current (A) 0.00 1.00 2.00 4.00 6.20 8.30 10.20 12.10 0.00 0.46 0.74 1.10 1.36 1.54 1.66 1.74 Table 3 Circuit with fixed resistor Point of graph gradient measured Resistance (?)
The experiment was also successful since there were few anomalies, only one for the fixed resistor. Thus it can be assumed that the results obtained were accurate given the sensitivity of our equipment. We tried to resolve these anomalies by doing these tests again, however this resulted in getting the same figure. We may assume that the equipment isn't to blame since it was kept the same throughout the experiment. The experiment was conducted in a safe environment and all precautions taken before the experiment paid off in that no accidents happened. It would have been practical in the interest of conducting a fair test to use averages for series of current readings. This could be done using two different sets of equipment, conducting the experiment on each set and averaging the values. This could help us reduce error margin in any anomalies found. It may have been interesting to investigate the same aim with a wider range and more sensitive set of equipment. Smaller graduations of voltage on the PSU would have allowed us to plot the graphs with more accuracy. If possible it would have been interesting to use a diode. However given the amount of time we had, it would not have been possible to further complicate the experimental design. We may also have adjusted variables such as the gauge, length and type of wire used to investigate the effect these factors have on ohms law. It may also have been of interest to us if we investigated how adjusting the circuit diagram would have affected our results. However this may have been a little advanced for our level at present.
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