What is Resistance? Resistance is caused by collisions between the atoms in the object and the electrons (carrying electricity), which are trying to move through the object. (R = resistance measured in ohms (W) ).
Basically resistance is the term used to describe an objects resistance to the flow of electricity Electrons lose their drift velocity only when they collide. The electrical resistance of a conductor is simply a measure of the potential difference required to maintain a current. Basically resistance is a representation of how many electrons are colliding, and how quickly. An electrical current is caused when free electrons moving through atoms are influenced by either a positive or negative charge.
This causes all the electrons to change course. This is what we call an ‘electric current.’ We can work out resistance using Ohm’s law: Ohm’s law states that the current in a metallic conductor is directly proportional to the potential difference across it provided the temperature is kept at a constant value. Resistance = voltage / current Hypothesis: I predict that the rules and factors mentioned in the hypothesis can be proved to be correct by the experiments. There are five key factors that affect the resistance of a wire. Temperature, cross sectional Area, Length, Insulation and Material. I am only going to investigate three of these factors, temperature and insulation being the ones I will not be investigating.
... due to the higher resistance. This then decreases the current, decreasing the temperature, decreasing the resistance, and increasing the current again. Going on ... of atoms and ricochet of them, slowing the electrons down and increasing the vibration of the protons. ... a classroom environment, there are many factors such as minor room temperature fluctuations, contamination's in the wiring materials ...
In these diagrams the circles represent atoms, and the arrows the flow of electricity. Below is a comprehensive guide to how these different factors influence the resistance of a wire: 1. Length: The Longer a wire is, the more resistance there is. This means for example…
that if a wire that is 2 metres long is compared to that of a wire that is 4 metres long, then the resistance of the second wire will be more or less double that of the first. That is if all the other factors were the same for example: both wires were 3 cm in diameter, 20 degrees Celsius and made of nickel. The reason for there being more resistance is that it takes a longer time for the electrons to flow down the wire, and therefore there is a greater chance of them colliding more. Think of a long motorway with a large amount of cars all trying to get to the same place at high speed- collisions are imminent. This means that the shorter the wire, the lower the resistance.
See Diagram Below: Diagram 1 2. Cross sectional area: Diameter is another factor that can have influence over the resistance of a wire. A thick wire will have a lower resistance than a thin wire. This is because the free electrons effectively have more space to move round in, and therefore fewer collisions take place.
Again, it can be thought upon as a congested motorway. Except this time the motorway is so large, that everyone can drive along quickly in their lane, and has no risk of collision. The larger the area, the more room there is for electrons to move round. The fewer collisions there are, the lower the resistance. See Diagram Below: Diagram 2 3. Material The material that the wire is made from can also affect the outcome of the experiment.
The amount of resistance is not the same in every metal. This is because all materials have a different number of electrons. The number of electrons also affects the resistance of an object. Imagine it as a motorway.
The more cars there are, the more chance of a collision there is. The fewer cars there are, the less likely it is there will be a collision. 4. Insulation Insulation affects a wire because you are wrapping in it a non-conductor. The stronger the insulator, the higher the resistance. 5.
... increase in resistance, due to frequent collisions. To do this I would use the same length and width of many different wire materials, using ... it, so it has twice the electrons too. Evaluation This experiment has gone satisfactory, but there have been certain things in ... a lot more accurate, because they have a smaller surface area on their tips than crocodile clips. This in effect would ...
Temperature Temperature affects the resistance of a wire, the hotter a wire is, the more resistance there is. This is because the free electrons are moving faster, and thus there is a higher chance of collision. However, when a wire is cold, the atoms move more slowly, and therefore there is a lower chance of collision. The Experiments Aim: The aim of this experiment is to find which factors affect the resistance of a wire, why and how.
Method: We conducted three different experiments, each to test one property. Material, length and cross sectional area (thickness).
Below is the method for each experiment: Method for Experiment one and two: Measuring the resistance of wires with different cross sectional areas (thickness) and measuring the resistance of wires made from different materials: Equipment: 1. A wire board, with wires of different thickness on. 2. Two voltmeters (one needs to be set to measure amps).
3. Wires, to make a circuit. 4. A power supply box. 5. Variable resistor.
Step one: Set Up a circuit like the one shown below: Diagram 3: Step 2: Note down the diameters and areas of each wire (or if you are carrying out the materials experiment, note down the materials) and put them into a table as the one below. Example Table 1: Wire Area mm 2 Area m 2 Resistance (ohms) 1/amps Voltage I (amps) Ohmmeter reading In the material experiment, just replace the area values with the type of material, see the table below. Draw out the two tables three times, for each experiment will be repeated three times. Example Table 2: Wire Material Diam mm 2 Resistance (ohms) 1/amps Voltage I (amps) Ohmmeter reading Step 3: Now it is time to take results. What you have to do is place the ends of the two wires in the sockets at each end of the wire on the wire board.
... choice of materials that we could use for the wire affects the resistance that we receive. A wire with too little resistance would be hard ... keep this the same by not changing the wire throughout the whole experiment. If the wire is heated, the atoms will move around ... up the circuit that we will use to take the readings. Using the equipment that has been checked we set up ...
Take down the readings for V and the readings for I. Repeat this act for the other five wires. Then repeat the overall experiment two more times. However, with experiment one, keep the variable resistor at a low setting, with experiment two put it on a medium setting, and with experiment three a high setting. Step 4: Set up a circuit with an ohmmeter, using the diagram below as a guide.
Diagram of a circuit: Method for investigating how length affects a wires resistance: Equipment: 1. A wire board. 2. A power source.
3. A ruler. 4. Some wires. 5.
A crocodile clip wire. Step one: Set up a circuit as shown in the first experiments, replacing one of the wires linking to the board with a crocodile one. You only need to do this experiment on one wire. Use the same wire board as you did for the cross sectional area experiment. Step 2: Repeat everything as in the first two experiments, except stick to one wire and vary the lengths by moving the crocodile clip up the wire. Set up a table like the one shown below.
Take ohmmeter readings as before. You do not need to repeat this experiment three times. Table for length: Experiment investigating length Resistance (ohms) Lengths (cm) Voltage (volts) Current (amps) 0 0. 036 0.
124 10 0. 036 0. 123 20 0. 036 0. 121 30 0. 035 0.
119 40 0. 034 0. 116 50 0. 033 0.
112 60 0. 032 0. 102 70 0. 03 0.
1 80 0. 028 0. 088 90 0. 023 0. 068 100 0.
025 0. 013 Diameter of wire (mm 2): 0. 98 Ohmmeter reading (ohms): 1. 8 Note: Be sure not to electrocute yourself by sticking conductors in the plug. Also be sure not to let the wires heat up too much. Obtaining Evidence Tables are attached to the back of the whole piece.
Analysing Data Conclusion: I have discovered from this experiment that resistance can be affected by many different variables and factors. There were obviously other variables affecting my experiments along with the one I planned, such as temperature. The longer the leave the power on the hotter the wires get, and therefore your results will not be perfect. From the four graphs I have made, I can determine many things. Firstly, I now know the metal with the highest resistance is Nichrome.
... (Loss I2 * R), where R is the resistance. A power factor of 1 will result in the most efficient loading of the supply ... that too much capacitance in an AC circuit will result in a low power factor just as well as too much inductance ... , wasted energy capacity, also known as poor power factor, is often overlooked. It can result in poor reliability, safety problems and higher ...
I have also been able to verify my predictions earlier on in the hypothesis section, with only a few anomalies. However, there were many prominent patterns throughout all of the graphs. But the graph of length against resistance however was not what I had predicted. Although all results shown on the graph are averages, the line seems to remain more or less straight until you reach the 100 cm mark, at which case it rockets to a resistance of 2.
0. This could be an anomaly, and probably calls for further inspection. The graphs of area and 1/area against resistance showed similar patterns. For instance, I am now sure that cross sectional area affects the resistance of a wire in the way I predicted. The thinner the wire, the lower it’s level of resistance. And vice versa.
I conclude that resistance is affected by the three variables I investigated. I also conclude my earlier predictions about free electrons in the hypothesis section were correct. This is true of all the three variables. This means my results support my original predictions.
Since we did not carry out a preliminary, my predictions were not based on practical work, but research. Also the results can be affected by the amount of power being used. The equation we can use for power in this case is: Current squared multiplied by Resistance = Power This means that in every case we can find the amount of power being used. For example if the current was 2 and the resistance was 2, then the power would be 32. This means that you can determine the amount of power relative to the amount of current and resistance etc. with each reading if you wanted to.
It is also very hard to make accurate conclusions about many of the materials in the experiment because many of them were alloys. This means that the number of electrons in each atom will differ to the number of electrons they had as separate elements. The material wires were also of different widths, and thus temperature and material were not the only variables at work. The graph of 1/area was also in inverse proportion to the graph of area against resistance because the reciprocal of the original readings was used. From this experiment however, we can tell some materials have a higher resistivity than others. That is to say some of the metals were better conductors than the others.
... explained earlier. Experiment two - These results were not as accurate as experiment one. I had predicted that the resistance should halve as area doubles, which ... kept the same at 2 V dc from a power pack. Both experiments will be done twice with different ammeters in case ... charge to jump along the line of atoms in a wire. Resistance is caused when these electrons flowing towards the positive terminal ...
Resistivity is the work used to describe how good or bad a conductor a certain material is. If the value is high, then the substance does not conduct electricity very well. If it has a very low resistivity value, then the substance is a good conductor of electricity. This means that I can assume from my readings that copper is a better conductor than Nichrome.
The equation for resistivity can be seen below: R = R = resistance and is measured in ohms () = length and is measured in metres (m) A = area and is measured in square metres (m 2) r = resistivity Graphs are attached to the back of the piece. Evaluating Evidence I think that my evidence is reliable enough for conclusions to be drawn. My plan was to investigate three factors, and I have done so. I repeated two of the experiments three times, and found that all the results were more or less the same each time. There was one anomalous result on the graph of resistance against length.
The final result, at 100 cm length was much farther apart from the previous result than all the other results had been. I think that this is due to either faulty readings or the fact that by the time I had come to taking my reading for 100 cm, the wire was very hot due to gradual heating. I think that my results are fairly reliable. It is clear that the wires gradually heated up over the course of the experiment, which brought in yet another variable, which was not originally planned in the experiment. This means that all my results are going to be a little wrong, and none of them will be perfect. There was not much I could do to solve the temperature problem, short of switching the power on and off and waiting for the wire to cool.
Which is dangerous, and would have cost me time. Although it would have been an improvement to the experiment, and made it more accurate. Another way to make the experiment more accurate would be to make all the material wires have the same cross sectional area, only then would the results be truly accurate. Even though copper probably is not as resistant as Nichrome, seeing as there is such a difference in cross sectional areas it is hard to tell. The evidence is not enough to support a firm conclusion in the case of the materials experiment, however I think the other two experiments were enough to support a firm conclusion. Temperature was not a planned variable, however it did play a part in the experiments.
... it's free writing. Reading will always be something that I can do all the time. Just put something in ... strange, but who knows, some of these "useless" readings could come in handy one day. Now if I could ... something that interests me. However, I don't enjoy reading books much. I've always lived a fast paced ... and not get a 'C' on my papers anymore. Reading on the other hand, is a different story. I ...
Wherever there is energy, there is heat and so it is very hard to control it perfectly. Temperature affects the resistance of a wire, so the wires tested last would have been of the highest temperature, and therefore there would have been more resistance. As I have mentioned before, one way to control this would be to switch of the power supply between taking each reading. Another way may be to insulate the wire, but that brings in a another factor, which would mean the experiment would be totally different. We did not have the time in class to switch the power off for a few minutes between taking each reading.