The Effect of a Varying Length of Wire on Its Resistance Aim === The aim of the experiment is to find out how varying the length of a wire affects its resistance. Prediction I predict that as the length of the wire increases, the resistance increases. Also that the resistance is proportional to the length of the wire, therefore as the length doubles the resistance doubles too. This is because the longer the length of the wire the more electrons (current) will be passing through, so therefore the more the possibility for the electrons to collide with the metal ions and cause the resistance to increase. Equipment -??? The following equipment is what we need for the experiment: 1. An ammeter: this is to measure the current that will pass through the wire (to find out the resistance= p.d (potential difference/voltage) Current (in amps) 2. A voltmeter: to find out the potential difference across the wire and so to find out the resistance= potential difference (voltage) Current 3. A beaker of water (50ml): this is so that the nichrome wire does not heat and so that heat does not affect the energy voltage inputted through and therefore if the wire heats up the energy input will not be efficient as if the current is high energy will be lost because of heat.
4. A power supply pack: This is to transfer the voltage energy through the nichrome wire. Also using a power pack is more accurate because this way it is better to ensure that the voltage generated is constant. 5. A rheostat (variable resistor): This is to vary the current across the circuit so that the potential difference can be measured with different range of current and so to calculate the resistance. 6. A coil of nichrome wire: This is so that to measure the voltage and current as different lengths of the wire are used each time, but the same type of wire is used for each experiment. 7. Clamps: These are to connect the wire to the circuit and to vary the length of the wire and to hold the equipment in place. 8. A ruler/ measuring tape: to measure accurately the length of the nichrome wire. Fair Testing To get a fair test all the factors that affect the resistance of the wire must be kept constant so that the length is the only variable. The factors that affect the resistance (which are to be kept constant) are:- 1. The cross sectional area of the wire, because as the cross sectional area increases, the resistance increases. Therefore the same thickness of wire should be used. Keeping the same thickness of wire will ensure more accurate results because if the wire was very thick, the amount of electrons flowing through will differ and therefore by having different thickness of wire each time will also affect the temperature. 2. The type of wire: nichrome wire is a good conductor therefore the same wire should be used throughout the experiment. If different wire was used then the results would not be accurate, as each different wire gives different results. Also some wires conduct electricity better than others and have voltage pass easily through. This would affect the results. 3. Temperature: As the temperature increases the resistance of the wire increases. Therefore a constant room temperature should be kept or it would be best if it was in a beaker of water so that the temperature of wire is kept the same, and for it to cool down after current has been flowing through it, the wire heats. 4. Voltage: I have also thought about keeping the voltage at a constant 5v, it is because the aim of the experiment is to vary the length of nichrome wire and finding out the resistance so keeping the voltage at a 5V constant out of the power pack is the best way to finding this information. Voltage is kept constant but varying the voltage through the variable resistor. Reliability To make the results as reliable as possible and to ensure better results I will do the following:
To repeat the experiment three times at least and get the average
of the three results and getting the average of the three results
for each length to get accurate results.
Checking if the voltmeter and ammeters have a reading zero before
starting the experiment, to ensure reliable results.
If non-digital ammeters and voltmeters are used then read at a
straight angle to get the right readings.
If there were any anomalous results to repeat them.
Readings -??- 1. The numbers of different lengths I will use are as follows: 30cm, 50cm, 60cm, 80cm and 90 cm of nichrome wire. 2. For each length of wire different voltages are used but limited only up To 5volts because if there was more voltage put into it, the wire might snap easily. 3. The experiments will be repeated three times ensuring better results, after having the results, then an average is calculated, after that the result which is closer to the average will be my original result. This is so that I get larger numbers of results and pick out the best I find in my view. After getting the results as closer to the average and as accurate I will note them down as my original results in this investigation. Then I can draw a more accurate conclusion to how a length of a wire affects its resistance. Measurements -????- 1) The current will be the independent variable. It is what is going to be changed deliberately (using the variable resistor rheostat) step by step for each reading. 2) The potential difference will be the dependant variable the size of this variable depends on the current. 3) The other variables will be controlled (kept constant) which are: v Temperature v Voltage v Type of wire v Cross section of wire Safety -?-
To keep a safe experiment , the circuit should be checked before
the power supply is switched on.
To keep clear of the wire while the experiment is processing,
knowing that the wire would be very hot (due to the flow of
current) and knowing that electricity is passing through it.
To keep clear from the water that the wire is in while electricity
is passing through it is dangerous because electricity runs
through fluids and is dangerous to touch the water.
As soon as the experiment is done, make sure about switching off
the power supply.
Method -?- 1. The equipment was set up as shown above in the diagram v The voltmeter must be parallel to the resistor. v The ammeter and rheostat must be in series. 2. Keep the voltage constant at 5 Volts (v), it is kept constant all the time to get accurate results and no anomalous results, because if there is a change in voltage the resistance rate will fluctuate. 3. Measure the length of the wire accurately, so that the different lengths of nichrome wire result in reliable results and graphs. 4. Vary current using the rheostat, so that to get different currents and relate to the potential difference. 5. Measure the current through the ammeter and to measure the potential difference through reading the voltmeter. 6. Repeat points 4 and 5 for the rest of the ranges of lengths (use a ruler and clamps to change the length of the wire. Results -?? For my results I had picked the perfect average to calculate the resistance In an accurate manner. I had to redo the experiment many times and find out some measurements and results from colleagues due to unsure results. Length Potential difference (Voltage) Current (amps) Resistance (v divided by I) 30cm 0.69 5.61 0.12 0.54 4.42 0.12 0.30 2.56 0.12 0.17 1.65 0.10 0.11 1.02 0.11 0.04 0.46 0.08 50cm 2.95 4.52 0.65 0.49 0.77 0.64 0.26 0.41 0.63 0.19 0.25 0.76 0.15 0.24 0.63 60cm 3.12 3.99 0.78 0.69 0.89 0.78 0.37 0.48 0.77 0.26 0.35 0.74 0.21 0.27 0.78 0.18 0.24 0.75 80cm 3.39 3.29 1.03 0.95 0.93 1.02 0.53 0.52 1.02 0.41 0.40 1.03 0.31 0.31 1 0.28 0.27 1.04 90cm 3.38 2.74 1.23 1.12 0.92 1.21 0.79 0.65 1.21 0.63 0.51 1.23 0.49 0.40 1.23 0.38 0.31 1.22 Other results obtained: Length Current (1) Current (2) Current (3) Current (4) Average Resistance 30cm 1.7 1.6 1.8 1.7 1.7 0.9 60cm 0.9 1.0 1.1 1.0 1.0 1.5 90cm 0.5 0.6 0.6 0.6 0.6 2.5 120cm 0.4 0.5 0.4 0.4 0.4 3.8 150cm 0.3 0.5 0.4 0.4 0.4 3.8 [image] Conclusion -???- I finally conclude that as shown in the graph above and according to my other graph?s gradients. It shows that as the lower the current is reduced the higher the resistance. It is because if there is low current then high resistance. This means that the energy input (voltage) has low efficiency since the output is less. According to my results table and graph, I found that the resistance increases as the nichrome wire?s length increases for example 30cm of wire equals to a much lower resistance than the readings on 90 cm of wire. Secondly most of my results show that the more the voltage the more the current. My readings also show that the current is not larger than the voltage either same or less. The gradients of my graphs indicate the actual resistance. Look at diagram below for further detail: Evaluation -???- I had many problems in this investigation because I had many anomalous results, which ruined my understanding and made me conclude the wrong points. Some results were okay but some I had to repeat and calculate an average. As you may have realized in my graphs, I have labeled some anomalous results to be looked at and analysed. I would really like to investigate a wider range of results e.g. thinking about having set up a different wire or having to adjust the cross sectional feature of the wire. The main reason why I think I had anomalous results was mainly because I should have organized my time and using my time wisely, during the experiment week. If I would redo this experiment I would think about: -Organizing my time better, and extending the investigation further. -I would like to change another variable and keeping specific variables constant. -I would have used another way of showing my results. I don?t think that my range of results was reliable. The problem I think was that the results were not repeated much. I should have thought about repeating them at least 5 times each (if I had the time and equipment). The pattern of my graphs kept repeating, nothing was changing in the way I thought it would. There wasn?t a huge change, but there was still a change just enough to make me understand the result. Some of my readings I never did write them in my table of results, although I actually did include them as part of my graphs. If I mostly had the time I would have changed the equipment I have used and I would have changed the variables mostly. It is because my curiosity lies in expanding and getting more evidence to have a better understanding of other different variables I could have used. If I could improve my work I would have improved on my : - organization and time limit - my results (get more accurate ones) - and do more graphs to show detail.

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