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To investigate how current affects the resistivity of a wire.

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Introduction

To investigate how current affects the resistivity of a wire. Planning Aim: the aim of this experiment is to investigate how current affects the resistivity of a wire. Discussion: atoms are made up of a positively charged nucleus surrounded by negatively charged electrons. In solids one or two of the outer electrons in each atom are used to bond with atoms that hold the solid together. In a metal these electrons are free to move throughout the solid to anywhere they want. These are usually known as "de-localized free electrons". An electrical current is a flow of charged particles and therefore the free electrons can flow through the metal if a voltage is applied to the metal. The resistance of a wire is where a metal wire is placed in an electric circuit and the voltage from the battery makes the electrons flow through the wire. They collide with metal ions whilst doing this and this process slow down the flow. Therefore resistance is the measurement of how easily the electrons can move through the metal- a low resistance means that the electrons can move easily and a high resistance means that the electrons cannot move so easily. The current is the measurement of how much charge flows per second. I=Q/t Current represents the number of electrons flowing per second, as the charge on each electron is the same. If the resistance is high ten the flow of electrons is slow and therefore the number of electrons per second is reduced, i.e. the current is reduced. If the metal is heated the metal ions will vibrate more thus there is a greater chance of an electron colliding with a metal ion and so the flow of electrons is reduced. (I.e. the resistance increases) The most common analogy is that if you consider yourself to be an electron and are walking through a crowd of people (the metal ions). ...read more.

Middle

Safety: To ensure that my experiment is safe I will have to be extremely careful when dealing with the electricity. I must be careful not to touch any wires while the power is on and those that have an electrical current passing through them, because I may get burned. Obtaining evidence Method: First I gathered all the equipment listed together and set up the circuit like shown in the diagram on the second page. I then checked that all the equipment about to be used was clean and in working order. I then set the power setting to two volts (for reasons stated earlier in my preliminary work). Then placed the piece of nichrome wire in its correct position. I then securely connected the two crocodile clips to each end of the wire and placed the meter ruler next to it. I then made sure that the first crocodile clip was level with the point 0cm on the meter ruler. The other clip was then placed at the positions I stated earlier, (from 0 cm to 100cm measuring every 10cm). I then made sure the ammeter reading was off as zero before I switched anything on. Then I turned on the power pack with one clip on 0cm and one on 10cm (to start with); I then read off the measurements from the ammeter. Then I switched off the power pack and record the results that were just obtained. In turning off the power pack I mad sure that the wire did not over heat and hence keep it a fair test (because the temperature affects the resistance). After the wire cooled down I moved the clip from 0cm to 20cm, turned the power pack on and started taking the reading for the current and voltage once more. After I'd taken all theses readings up to 100cm (with 10cm intervals), I then did the same again for repeat readings. ...read more.

Conclusion

I kept the cross-sectional area of the wire the same throughout the entire experiment to also help make it a fair test. I did this by using the same piece of wire for each measurement. In not changing the wire I also kept the resistivity of the wire the same as the material of the wire could not and did not change. If you look at the graph for my initial readings you can see there's one anomalous result. This is occurs when the length of wire is 20cm. The anomalous result could have happened because either the wire may have been over heated for that particular reading, hence the resistance increases, or, the result may have been misinterpreted due to human error, i.e., I may have recorded the incorrect reading from the ammeter or put the crocodile clips on the wrong length of the wire. However in spite of this minor setback and despite these problems this experiment provided me with good enough results. I could have repeated the experiment even more times for even greater reliability. From my results I was able to produce accurate graphs and the points on these graphs are close to the line of best fit on the graphs. However, an investigation can always be improved upon and I feel I could improve my investigation by: 1) Using a digital ammeter to reduce human error. 2) Leaving the wire time to cool down between readings to help make it a fair test. 3) A longer wire 4) Water bath 5) Higher voltage 6) Variable resistor 7) Volt meter after power pack In my opinion my results were sufficient enough to form a good conclusion. I took 50 readings in total. All these points on my graphs are close to my line of best of fit, apart from my anomalous result, so I think I am right in saying that my results are accurate and can support my conclusion. ...read more.

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