Temperature of wire, as more voltage continuously flows through wires, it’s possible and very likely that they may heat up. To prevent this, use a switch or simple disconnect the circuit when not in use, this stops the voltage flowing and therefore is less likely for the wire to get hot.
It is possible for a wire to suddenly snap and may come up, although this is very unlikely, it’s best to stay aware of this factor and wear goggles.
Fair Test
In every investigation it’s important to perform a fair test, if an investigation / experiment is not as fair as possible then the results gained may not be reliable or accurate.
To ensure my investigation is fair I plan to ;
Keep the voltage as constant as possible, monitoring it at all times and using a variable resistor, which can change the voltage to whichever voltage I plan to use.
Disconnect the circuit after every length / thickness of wire to ensure it doesn’t heat up and affect the next reading.
Keep the temperature in the room as constant as possible. This is very difficult
Method
- Set up apparatus as shown on diagram 1
- Take the readings from the preliminary work to check if there is a suitable difference between readings, if not, use a wider or smaller range of lengths or thickness or carry on if readings are suitable.
- Connect the first length of wire you plan to use.
- Move the variable resistor so that the voltage reading lies on 1.
- Take the reading off the ammeter and record it.
- As soon as the reading has been taken, disconnect the wire as it may heat up
and this may effect following readings
- Repeat steps 3,4,5 and 6 for the same thickness but a different length.
- Once all the results for length have been taken using one thickness of wire, change the thickness and repeat steps 3,4,5 and 6.
- Take repeat readings for every thickness and length in order to obtain more accurate readings.
Diagram 1
Analysis
In the experiment, I was investigating how the length and thickness of a wire affects the resistance. By looking at graph 1 it’s possible to see that as the length of wire increases, the resistance does also. From my graph on the previous page, I can see that the resistance of the wire is directly proportional to the length of the wire. I know this because the line of best fit is a straight line through the origin showing that if the length of the wire is increased then the resistance of the wire will also increase in proportion to each other. The line of best fit is a straight and it goes though (0,0) if there is no length, there is no resistance proving that the resistance of the wire is directly proportional to the length of the wire. This proves my prediction right. The length of the wire affects the resistance of the wire because the number of atoms in the wire increases or decreases as the length of the wire increases or decreases in proportion. Not every point lies on the line of best fit, but there are no erratic anomalies. At the length of 40.0cm’s there was a resistance of 3.03 Ω, the line of best fit crossed 40.0cm’s at approximately 3.22 Ω, and this was the largest distance from a point to the line of best fit.
The resistance of a wire depends on the number of collisions the electrons have with the atoms of the material, so if there is a larger number of atoms there will be a larger number of collisions that will increase the resistance of the wire. If a length of a wire contains a certain number of atoms when that length is increased, the number of atoms will also increase. If the wire is half the length of a certain wire, it would have has half the number of atoms, this means that the electrons will collide with the atoms half the amount of times. In addition, if the length of the wire was trebled or quadrupled, then the resistance would also treble or quadruple.
From the graph it is easy to tell that the theory is correct and therefore my results reliable. From my results table and graph, I can see that my results that I collected are quite reliable and accurate. I know this because my results table shows a very few, individual anomalous results. Most points are extremely close to the line indicating that my results are accurate.
I think that my results are suitable to confirm my prediction and support a conclusion. I know this because outside resources (Textbooks and internet) say that ‘the length increases in direct proportion to the resistance.’
Graph two shows a similar trend as graph one. Both lines on the graph show that when the factor being investigated is used then the resistance increases proportionally to this factor. Although both show similar trends, the graph that shows the effect of thickness on resistance is slightly different to graph one. Both thickness and length effect resistance in the same way, when they increase so does the resistance, but when the thickness is doubled, the resistance is almost halved compared to when the resistance is measured changing lengths.
A wire consists of fixed positive atoms or nuclei surrounded by electrons, some of which are basely bound and will move under the influence of a voltage. The nuclei are vibrating and obstruct the flow of electrons. Nuclei of hot wires vibrate more increasing the resistance. Increasing the length increases the number of obstructing nuclei (double length = double no.) so increases the resistance. Increasing the diameter increases the number of charge carriers at any cross sectional point. More charge carriers (electrons) means greater current or less resistance, this is why the line of best fit on graph two is lower than on graph one.
Evaluation
From my graph I can see that my results that I collected are very reliable. I know this because my graph does not show any individual anomalous results. I can see on the graph that none of the results plotted are anomalous because all the points lie along the same straight line.
When I was measuring the lengths of the nichrome wire, my measurements might have been slightly inaccurate as the rulers used might not have been exact, and it was difficult to get an accurate reading of length by eye, as the wire was not completely straight, so it may have been of different thicknesses throughout the length. This would have contributed as a slight error in my results. As this factor probably only made a slight difference, it did not affect my results.
The crocodile clips and the connecting leads could have affected the fairness of the experiment. They are a different type of metal from the nichrome wire and may have different properties and therefore different resistance. Therefore the resistance of the nichrome wire showed up on the multimeter was slightly more than it actually was. To solve this problem, I would have found out the resistance of the connecting leads and crocodile clips before each experiment and minus it from the overall resistance of the nichrome wire plus the connecting leads plus the crocodile clips. I do not think I could improve on the way the experiment was done because my results were very accurate, as I had no anomalous results. I also found that the experiment was quite easy to set up, as it was simple and uncomplicated.
To extend my investigation, it’s possible to explore these factors:
Material – In order to broaden the investigation it’s possible to carry out the experiment as done with the length experiment but by sticking to one length and varying the material. By doing this it’s possible to compare how each material affects the resistance and conclude which is better for certain appliances.
Temperature – Temperature can have an effect on any experiment calculating resistance as any wire can be heated if connected to a circuit too long. To investigate how temperature has an effect on resistance, you can heat a certain wire, record the temperature using a thermocouple and then connect it to a circuit and record the resistance.
Material:
To do this, I would set up the experiment the same as with the thickness investigation. In order to investigate how material changes the amount of resistance, I would firstly find different materials e.g copper wire, nichrome wire etc and conduct a preliminary test to see if the different materials had enough difference of values to show the effect of the material on resistance. If all values of the materials were similar, I would be persistent in finding materials that had significantly different readings. When I had found suitable materials, I would connect the apparatus the same as Diagram 1, and take readings for each material separately, making sure not to heat the wire as it may cause the wire to effect the final results.