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Then take the 30cm ruler with mm measurements and make these marks on the planks of wood 100% accurate distances. Ensure that the wire is tight and will not sag pre-experiment – giving extra accuracy compared to it not being a tight wire. At each 5cm Point I will take a thickness reading of the wire using the micrometer to assess how accurate the thickness of the wire is – if it has different thicknesses in different parts of the wire. When starting the experiment always remember to leave 30seconds for the wire to cool between each distance change or rerun.
Start with both crocodile clips touching each other at one end of the wire. This will give the smallest amount of resistance shown in the circuit. Then add 50mm to each measurement working up to 500mm. After each distance has had the current measured at 3V supply voltage 3 times move up to the next distance, repeat until 10 results have been gathered. (10 results average). Safety Precautions – Due to the nature of my experiment there are no obvious risks to health apart from burning yourself on the wire if you touch it whilst hot.
I have thoroughly assessed all aspects of my experiment and deem only a few items to be of very minimal risk. These risks are covered mainly by common sense but listed here as a reminder: Never operate equipment, which you are not familiar with or competent to use. Always switch off equipment after you have finished using it or between each measurement to allow the wire to cool. Never use faulty equipment, report it immediately to a member of staff. Keep gangways clear of obstructions. If you need to keep bags or other articles with you, store them so as not to cause a trip or other hazards.
Keep electrical devices away from sinks and keep all liquids clear. No types of safety goggles or gloves are required for this experiment as it doesn’t involve anything moving but only hazardous to touch (burning potential) But avoiding touching the wire will prevent this, although the burn from the wire wouldn’t be very severe if it did happen. RESULTS Current in Amps (A) Length (mm) Voltage (V) Repeat 1 Repeat 2 Repeat 3 Average of Current (A) Resistance (ohms) 00 amps = Resistance Resistance = constant (resistivity) ? length Area of cross-section You can calculate the resistance if you know the resistivity, I will calculate the resistance of the wire at 25cm point (250mm).
Resistivity = resistance ? area of cross-section “(Cross-sectional area of wire =? r2)” Length = 14. 06×10-9m2 Resistivity = gradient ? area of cross-section Gradient is calculated by taking Resistance Length So: (6 – 0. 71) / (0. 5 – 0. 05) Gradient = 11. 75 ? /m x 14. 06×10-9m2 = Graph of averaged results from the graph included I can conclude that increasing the length of a wire increases its resistance. This is clearly shown from the positive correlation line in the graph with a fixed gradient.
From my results on the averaged results graph you can clearly see that there 2 anomalies. EVALUATION After finishing my experiment and looking over my method and how I worked out certain things, I feel that the graphs should have shown the results to be proportional to the length of the wire. But this wasn’t fitting the trend of my results. After drawing up the graphs and studying the results table, all of the results for average of current are gradually increasing dis-proportionately until 50mm and 0mm where they seemed to have a huge difference in resistivity compared to other distances.
This is expected but not to the scale that it occurred. The results we got could have been through human error in testing. Looking back on the final experiment we did, the crocodile clips were not as accurate as they could have been in measuring precisely the distances. Also, I don’t think that we left the wires for 30seconds between each reading due to time restrictions. This I feel has had a negative impact on some of our results has they had to be collected over two separate sessions.
We kept the same power pack but the wires were mixed and most likely causing different wires to be used. BUT we did retest the wire to ensure we had the correct thickness, just the wire could have been worn down. We did a further 3 tests on the wire using the micrometer to get the thickness of 28 swg again. At 10cm, 25cm and 45cm, using more accurate methods than a rather ‘chunky’ crocodile clips will help remove the measurement error. A different method to sorting the cool down period would be to have more time and possibly reduced the number of distance increments tested over.
To get the most accurate readings from our ammeter and voltmeter we used digital models to get results to the 2nd decimal point. Temperature surroundings have to be taken into consideration as they are almost impossible to maintain perfectly. Sunlight frequently shone through the windows and this could have easily caused slight but important differences in the wire resistivity. Resistance in the wire can also be increased by very small kinks or lumps in the wire, again the affect is minimal but all the small differences add up.
IMPROVEMENTS TO BE MADE I am quite pleased that we did the preliminary test and ironed out a few problems, there are some still that need addressing. Instead of crocodile clips use thinner metal strips or pointers to increase accuracy of distance taking. To ensure environment conditions stayed the same I would use an air conditioned room. I could possibly repeat the readings 5 times instead of 3, but 3 is acceptable. The extra 2 repetitions would be to add to the accuracy although it is not deemed absolutely necessary.
Longer lengths of wire than 50cm could be used to see for further correlation of results on distances 50cm+ Leave a bigger gap than 30seconds between each reading say 1minute, this is impractical due to time restrictions but is a sacrifice for more accuracy. To ensure environment conditions stayed the same I would use an air conditioned room. Get a more reliable power supply that isn’t old and isn’t analogue. It was hard setting the voltage to the correct setting and needed to be constantly tested with a Voltmeter to ensure accuracy which made the experiment take much longer.
EXTRA INVESTIGATION There are many different ways to further the experiment, but the most simple and interesting to me would be testing different thicknesses of Nichrome wires. I could use both 30 and 32 swg thicknesses of wires available to me. This would be with the same method, just the difference in wire thickness. It would have to be the same method and setup to allow a fair comparison to be created. As I mentioned before about thickness of wire making lesser resistance due to the amount of electrons colliding with metal ions, this would have an effect on the wires resistance…but to what extent is what I would find out.
The thicker the wire the more electrons are available to carry the charge along and the more space available reducing the amount of collisions. I would think that the cross-sectional area of the wire wouldn’t be as directly proportional to the resistivity as the 28 swg wire. The resistance should be inversely proportional to some extent where increasing wire length was x2 resistance the increase of wire thickness would mean DIVIDE by 2 making less resistance.