# The Thickness of Nichrome Wire And Its Effect on Its Resistance

Introduction A current is the flow of negative electrons around a circuit. Electrons get pushed out of the negative pole of the cell and drift slowly round the circuit, from atom to atom in the wire, to the positive pole of the cell. A current flowing in one direction like this is called direct current. (d.c.) A cell pushes these electrons around a circuit. It acts as an electric pump. Different cells provide electrons with different amounts of energy, or have greater ?voltage.? When a cell is connected to lamps, the voltage pushes the electrons around the circuit. The energy to do this comes from the chemical energy stored inside the cell. Batteries are a store of chemical energy and the wires are able convert this into electrical energy to be carried around the circuit. The energy that the electrons carry is converted into light energy by the bulbs. After the electrons have provided the bulb with the energy to light up, they carry on their journey around the circuit, but with less energy. Voltmeters measure the amount of energy that electrons have.
Nichrome Wire Everything within a circuit has a level of resistance, measured in ?ohms.? Resistance is a force which opposes the flow of an electrical current around a circuit so that more energy is required to push the charged particles around the circuit. The nichrome wire contains free moving electrons, which resist the flow of the negative electrons supplied by the cell. Therefore, for the electrons to flow through the wire, the voltage must increase. The amount of energy contained by the electrons must be greater than that of the free moving electrons in the nichrome wire, so that they can flow freely. As the voltage increases, so does the resistance. As the length of the nichrome wire increases, there is more space for the free moving electrons to move around inside the nichrome wire. This means that as the electrons try to pass through the wire, they will be resisted by more free moving electrons, causing the resistance to increase. This again increases the force needed to get passed the free moving electrons, raising the voltage. [image] Path of Electrons Free Moving Electrons Path of Electrons This diagram shows the charged particles in competition with the free moving electrons contained within the nichrome wire. It shows how the electrons have to find a route through the free moving electrons which are constantly vibrating and moving slowly around. To find their way through the sea of free moving electrons, they must move around, which uses energy which is why the voltage increases as the resistance increases. Prediction I predict that as the length increases, the resistance will increase in proportion to it. Proportional means that as the length doubles, so too will the resistance. We already know that as the voltage increases as the resistance increases, to provide the electrons with enough energy to bypass the obstacle in their way. This obstacle is the free moving electrons within the nichrome wire, which oppose the electrons as they try to flow freely. As the electrons from the cell move through the wire, they collide with the free moving electrons. Resistance is where the electrons flow towards the positive ions and crash into other atoms that lie in their path. As these atoms collide, kinetic energy is transferred between the atoms. As this energy is transferred from atom to atom, they start to accelerate. However, atoms will always knock into each other, meaning energy will be continually transferred. Atoms move, collide and then transfer energy, creating a circular-like pattern. This transfer of energy is what causes resistance. [image] Therefore, if we double the length of the wire, the amount of free moving electrons within the wire is also doubled. The more electrons there are, the more collision there will be, meaning more energy is transferred and the resistance will double. Energy is never lost or made; it is always converted into a new type of energy or wasted. Apparatus Crocodile Clips 50cm Nichrome Wire 2 Cells Voltmeter Ammeter Insulated Wires Ruler Safety There are many safety precautions I should consider before I start this experiment.
I should definitely not carry this experiment out near water. If
the water comes into contact with the metal as someone is touching
the nichrome wire to change the length, it could cause an electric
shock.
Do not leave the circuit switched on when we are not using it, as
it could heat up the wire, making it very hot to deal with when
wanting to change the length.
Variables To ensure our experiment was fair, we only changed one thing, called the input variable. This was the length of the nichrome wire. We also controlled a number of things again to ensure reliability when carrying out the tests. We did not change the number of cells, the voltmeter or ammeter, the nichrome wire we were using or the leads we used to connect the different contents of our circuit. Method [image][image]Firstly, we connected the two cells together using the connecting wires and then joined one to the ammeter in series. We connected the nichrome wire into the circuit using the crocodile clips. We measured the certain length we required the nichrome wire to be by using the ruler. As voltmeters have to connect in parallel, we used two more connecting leads to connect the voltmeter. [image] Crocodile Clips [image]I will use measurements from 10cm to 50cm at 5cm intervals. These are easily measured by the ruler and have a good range. They will produce a clear graph. I will also repeat my results three times and take an average for reliability and accuracy. I must take 3 results for every length for the voltage and the current. I will then take an average for every length for these. Using these results, I will find the resistance. To work out the resistance, I must firstly find the voltage and current, then use this formula to work out the resistance:- Resistance? = Voltage (V) / Current (I) So, for example, if I had an average voltage of 1.71 and an average Current of 1.24, the resistance would be: 1.71 / 1.24 = 1.38 ohms To connect the crocodile clip to the nichrome wire, we will measure the length we want it to be using the ruler, and then grip the nichrome wire using the clips. As the length required increases, the distance between the crocodile clips will obviously change. We will ensure we measure the lengths accurately by reading the scale on the ruler closely. After every reading, we will give the nichrome wire 10 seconds to cool down, to ensure it does not become too hot and dangerous. Results Length (cm) Average Current (amps) Average Voltage (volts) Resistance (ohms) 5.00 1.24 1.71 1.38 10.00 0.93 2.20 2.37 15.00 0.75 2.42 3.23 20.00 0.63 2.81 4.46 25.00 0.53 3.00 5.56 30.00 0.45 3.12 6.93 35.00 0.41 3.24 7.90 40.00 0.36 3.26 9.59 45.00 0.31 3.30 11.00 50.00 0.28 3.40 12.14 Conclusion During our experiment, we found out a lot about the way in which resistance works at different lengths of a nichrome wire. I predicted that as the length would be proportional to the resistance. We learnt that generally as the length doubled, so too did the resistance of the nichrome wire, proving our prediction was correct and accurate. As the length of the nichrome wire doubled, so too did the number of electrons within the wire, giving a higher resistance. As the electrons from the cell move through the wire, they collide with the free moving electrons. Resistance is where the electrons flow towards the positive ions and crash into other atoms that lie in their path. As these atoms collide, kinetic energy is transferred between the atoms. As this energy is transferred from atom to atom, they start to accelerate. However, atoms will always knock into each other, meaning energy will be continually transferred. Atoms move, collide and then transfer energy, creating a circular-like pattern. This transfer of energy is what causes resistance. The error bars that I have drawn on my graph show the range and accuracy of the readings that I took. The longer these bars are, the less accurate my readings were. Towards the beginning of the experiment, with the first three readings we took our error bars are fairly small. However, as we begin to calculate the resistance at longer lengths, our error bars begin to grow. At 25cm, my error bar is very tall. This could have been because we did not measure this length very accurately. However, it could also have been because we did not leave the nichrome wire long enough to cool down. This would have meant the atoms within the wire were colliding with other atoms very quickly at high speeds before we began to take the next reading, meaning a higher resistance. Our error bars could have begun to grow as the length of the wire lengthened because of its temperature. Perhaps we should have let the wire to have longer to cool down, so that the particles within it were not too hot. Heat acted as another variable here, meaning the points we plotted did not all fit along our line. At 20cm, we recorded the resistance as 4.5 ohms. However, if our experiment had been accurate enough, at 40cm the resistance should have been 9 ohms. However, this was not the case. Instead, we ended up with a reading of 9.5 ohms, reinforcing the fact that our measurements and temperature played a big part in the accuracy of our results. When I compared my results with other people, I found that my results were fairly accurate. However, more of their points lay on their lines. Evaluation I was generally very pleased with our method and the way in which we carried out our experiment. However, if I was to carry out the experiment again, there would be things that I would change. I would make sure I could read the ruler accurately, and ensure the temperature we were working in was controlled. I would use a straight ruler and maybe use a clamp to straighten out the nichrome wire. I could also work out an average using four or even five results, although this would be time consuming. However, it would make my results very accurate. I could also continue my range of lengths up to 100cm at 5cm intervals. This would make my graph look very professional and extensive. The error bars that I have drawn on my graph show the range and accuracy of the readings that I took. The longer these bars are, the less accurate my readings were. Towards the beginning of the experiment, with the first three readings we took our error bars are fairly small. However, as we begin to calculate the resistance at longer lengths, our error bars begin to grow. At 25cm, my error bar is very tall. This could have been because we did not measure this length very accurately. However, it could also have been because we did not leave the nichrome wire long enough to cool down. This would have meant the atoms within the wire were colliding with other atoms very quickly at high speeds before we began to take the next reading, meaning a higher resistance. Our error bars could have begun to grow as the length of the wire lengthened because of its temperature. Perhaps we should have let the wire to have longer to cool down, so that the particles within it were not too hot. Heat acted as another variable here, meaning the points we plotted did not all fit along our line. At 20cm, we recorded the resistance as 4.5 ohms. However, if our experiment had been accurate enough, at 40cm the resistance should have been 9 ohms. However, this was not the case. Instead, we ended up with a reading of 9.5 ohms, reinforcing the fact that our measurements and temperature played a big part in the accuracy of our results. Our experiment spanned over two lessons, meaning the nichrome wire was being used in two different environments. This could have had an affect on the resistance. Due to the varying room temperatures in the different atmospheres, the atoms within the nichrome wire may have been moving slightly faster. This could have meant the resistance was higher in the hotter room, as the atoms had more energy so were able to move quicker. As the atoms had more energy, they collided with the free moving electrons a lot faster and passed on more energy, giving unfair results. As I can see on my graph, our best fit line on our graph does not cut through every point I plotted, indicating slightly inaccurate results. We do have some anomalous results. On my predicted graph, I plotted a best fit line that cut through every one of my points, showing excellent accuracy and very precise results. The predicted graph showed that at 50cm, the resistance of the nichrome wire should have been 10 ohms. However, for numerous reasons, we ended up with a reading of 12.15 ohms. There are many reasons as to why this may have been the case. When I measured the lengths of the nichrome wire, my measurements may have been slightly inaccurate as it was difficult to measure the exact length I wanted by eye. This was due to the fact that the wire was not straight and when we tried to straighten it out, it was still slightly bent in places, meaning each length may have been slightly shorter than intended. The ruler we used was also bent and difficult to straighten, again meaning our lengths may have been wrongly measured. For example, due to the fact that the ruler was not straight, when we tried to measure 10cm, the actual length of the nichrome wire we measured could have been roughly 9.8cm. I could further my conclusion by looking at other things that could influence the resistance in a nichrome wire. This could include temperature. If I were to change the temperature that the nichrome was subjected to, this is what I predict would happen. I feel that if the temperature were to increase, the increase in energy would cause the atoms in the wire to vibrate quicker and collide more regularly. More energy would be transferred and so more and more atoms would be hitting each other. The increase in collisions would mean an increase in resistance.

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