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 an increasing voltage and current is passed through a filament lamp the resistance would increase in an irregular fashion, so that a graph similar to the one given below would be seen (figure 1). This curved 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 a straight line graph would be obtained (figure 2) this is explained in figure 3. 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 the experiment, as using several different wires or tangled wires during the experiment could lead to varied resistance and poor fair test (Figure 6).
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 variables in this experiment are the resistors and 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 (?) Throughout experiment (10.92) ~11 Table 4 Circuit with fixed resistor Point of graph gradient measured Resistance (?) A 2.86 B 6.67 C 32.70 Analysis of Results Both graphs produced results that should be expected by the types of resistor used. The graph for the fixed resistor is a straight line through the origin. The slope of the line was unchanged i.e. no tapering off. This is what should be observed when fixed resistors are used.
The experiment was also successful since there were few anomalies, only one for the fixed resistor. Thus it can be assumed that our results 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 can assume that the equipment is not 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 as no accidents took place. To conduct a fair test it would have been practical to use averages for a series of current readings. This could be done by using two different sets of equipment, conducting the experiment on each set and averaging the values. This could help us reduce the margin of error 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 increases 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. We may also have adjusted variables such as the thickness, length and type of wire used to investigate the effect these factors have on Ohm's law and our graphs. we would also investigate how changing the circuit diagram would have affected our results.
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