The risk of overheating in the circuit was minimilised by using a long enough length of wire and by using less than 3 volts.
Fair Test
There are many variables affecting this circuit. According to Ohm’s law we need to keep the circuit at a constant temperature to ensure accurate results. This will be accomplished by turning off the circuit when it is not in use. We will also need to keep all of the equipment the same. This will be easy to do if all of the results are taken on the same day. The same readers will also have to be kept for each stage of the experiment.
Equipment
Ammeter
Voltmeter
Wires
Power Supply
Fixed
Variable Resistor
Thermometer
Circuit Diagram
Variables
I am going to vary the current in the circuit with the use of a variable resistor. The current and voltage will be affected by this change according to Ohm’s law (resistance = voltage/Current). The equipment will be set up according to the circuit diagram. The change in resistance will also change the current and voltage, which can be monitored on the ammeter and voltmeter. This is expected because of our knowledge of Ohm’s law. Resistance, current and voltage are all connected. To adapt for the inevitable increase in temperature along the wires I will include a switch to the circuit. I will turn the switch off for the periods between each part of the experiment, when the circuit is not in use. This will reduce the wire temperature back to room temperature.
The length of a wire can also affect the resistance in a circuit. For example if you decrease the length then you increase the resistance. The width and material of a wire can also affect the resistance in the circuit. These factors will all be kept the same in this experiment.
Method
1. Gather the equipment -
Ammeter
Voltmeter
Wires
Power Supply
Fixed
Variable Resistor
Thermometer
2. Set up the equipment according to the circuit diagram.
3. Prepare a results table to include ammeter readings, voltmeter readings and thermometer readings for each result. There will have to be 2 other identical tables and an averages table, to filter out any anomalous readings.
4. Set the variable resistor to its lowest setting and then take the first reading.
5. Move the resistor up to gather the next result.
6. Continue this process to get another 4 results, repeating each part of the experiment 3 times.
7. Draw a graph of the results and indicate any anomalous readings.
8. Draw a conclusion, expanding the anomalous readings and what could have caused them.
9. Write an evaluation to discover other possibilities for further experiments.
Prelims
I will conduct a preliminary test to ensure that all the factors in the experiment are nominal and are to my satisfaction. Any unexpected events will be dealt with before hand. The proposed range for testing is 0 – 1A.
Reliability
I know that the results will be accurate because having a second experiment will check them. Any anomalous readings will hopefully be averaged out and will not have a significant impact on the final result.
Measurements
The measurements will be recorded in ohm’s, volts, and amp’s and also in degrees.
Proposed Range
I will hopefully get a range of 0-1 amps during the experiment.
Hypothesis
I predict that when the resistance in the circuit increases the current and the voltage will decrease, according to Ohm’s law (resistance = voltage/Current).
As the resistance increases there will be more ‘hurdles’ for the electrons to conquer as they travel around the circuit, and this is why the voltage and current will decrease. As long as the temperature remains constant this hypothesis will be accurate. The resistance will be proportional to the current.
Obtaining Evidence
From the preliminary tests I have corrected the problems in the experiment and have prepared a results table, the table that my conclusion will be based on.
Results Table
The average result was 0.7 Ohm’s for the experiment. The average temperature for the entire experiment was 21ºC.
Analysing the Evidence
My evidence is sufficient for a firm conclusion because the graph has no anomalous readings. We had to test the circuit twice because the preliminary test was a failure. We had unfortunately set the ammeter to the wrong setting, which was not apparent until after the experiment. The graph would not have been a straight line of resistance, indicating that the results were wrong.
The second test was a success. I have drawn a graph for this that had a resistance of 7.0 Ohm’s; the graph has also passed through the origin, which was originally expected. There were a few anomalous readings, however they were filtered out in the preliminary testing stage.
All the equipment was kept the same and the temperature also remained constant.
I can see clearly from the Results Table and graph that resistance is proportional to current and voltage. As the resistance increased so did the current and voltage. My hypothesis was nearly correct except that I was mistaken about the direction of results in proportion to resistance. I thought that the current and voltage would decrease as the resistance increases. It was the other way around, they both increased, proportionally.
I have concluded that the amount of resistance in a circuit affects the flow of current through a circuit. My Results Table and graph prove this. I have also proved Ohm’s law correct, that when current and voltage are altered at room temperature the resistance changes proportionally.
Evaluating the Project
The experiment was a success. This is clearly shown in the Results Table and on the graph of results. Our method was followed precisely, and all instructions about safety and a fair test were carried out.
The evidence was reliable because the graph was a straight line. This proves that the resistance was always the same. My results were fairly accurate and provided a fairly accurate graph.
If I had the chance to conduct an experiment like this again I would change the voltage as well whilst keeping the resistance and current the same to prove Ohm’s law correct. I would then be able to cross-reference the results and make a full investigation of the brief. The method for the next experiment is shown below.
- Set up the circuit as shown in the original circuit diagram.
- Prepare a results table to record the data from the circuit. It should include voltage and resistance readings. The resistance will be calculated as before.
- Instead of a variable resistor it may be a prudent decision to use a fixed resistor. The results will be taken more accurately and will keep it a fair test.
- Repeat each part of the experiment twice, to gather average readings and to filter out any mistakes.
- Draw a graph of the results to compare with the graph of current against voltage.
- Draw another conclusion and evaluate the investigation, stating how it worked and what went wrong.
I would have also liked to make the recordings with an analogue reader to test the difference in accuracy between an analogue reader and a digital reader. This would have also been an interesting investigation.
