For my GCSE physics coursework I intend to investigate the resistance of a wire and specifically how the length of the wire affects the resistance.Firstly I shall do some initial research to determine what resistance is, what affects it in general and anything else that I think will be relevant to my investigation.Then I will plan and carry out my experiment, recording the results.
I shall then collect and analyse the results, drawing a logical conclusion from the results obtained.Lastly I will do an overall evaluation of my investigation.ResearchWhat is resistance?The definition of resistance in Hutchinson’s Encyclopedia:”In physics, the property of a conductor that restricts the flow of electricity through it, associated with the conversion of electrical energy to heat; also the magnitude of this property. Resistance depends on many factors, such as the nature of the material, its temperature, dimensions, and thermal properties; degree of impurity; the nature and state of illumination of the surface; and the frequency and magnitude of the current. The SI unit of resistance is the ohm (?).”Metals conduct electricity because the atoms in them do not hold on to their electrons very well, this means that free electrons, carrying a negative charge can jump along the line of atoms in a wire.Resistance is caused when these electrons flowing towards the positive terminal have to ‘jump’ atoms.
So if we double the length of a wire, the number of atoms in the wire doubles, so the number of jumps doubles, so twice the amount of energy is required: There are twice as many jumps if the wire is twice as long (in theory you would use twice as much energy running a 800 meter race than a 400 meter race).Therefore if the length of 1 wire is 2cm and the length of another wire is 4cm then I predict that there would be twice as much resistance in the second wire.Also the thinner the wire is, the less channels of electrons in the wire for current to flow, so the energy is not spread out as much, so the resistance will be higher.What Affects Resistance?Wire length:If the length of the wire is increased, then the resistance will increase. This is due to the electrons having a longer distance to travel and so more collisions will occur. Due to this, the length increase should be directly proportional to the increase in resistance.Material:The type of material will affect the number of free electrons, which are able to flow through the wire.
The number of electrons depends on the amount of electrons in the outer shell of the atoms, so if there are more atoms then there are more electrons available. If the material has a high number of atoms, there will be a higher number of electrons. This will cause a lower resistance because of an increase in number of electrons.Wire diameter:If the wire’s diameter is increased the resistance will decrease. This is due to the increase in space for the electrons to travel through. Because of this increased space between the atoms, there should be fewer collisions. If the cross-sectional area of the wire were greater, the resistance would be less because more current will be able to flow through the wire.
Temperature:If the wire is heated up, the atoms in the wire will start to vibrate more rapidly. This will cause more collisions between the electrons and the atoms, due to atoms moving into the path of the flowing electrons. This increase in collisions means that there will be an increase in resistance.Wire density:If the wire has a higher density, the resistance will be higher. This is due to the wire having more atoms in a smaller space, creating smaller and less gaps for the electrons to flow through. Because of the increased lack of space there should be more collisions.Ohms LawThe direct definition of Ohm’s Law is: “Provided that the temperature remains constant, the ratio of potential difference (p.
d.) across the ends of a conductor (R) to the current (I) flowing in that conductor will also be constant”.Basically this states that:Voltage = Current x Resistance or V = IR.Voltage is the driving force that pushes the flow of electrons, or current around the circuit.
From the equation it is possible to see that if the voltage and current are known, then, by re-arranging the equation so that it is:Resistance = Voltage / Current or R = V/Iwe can tell the resistance of the circuit therefore allowing us to record some of the variable factors that effect the resistance of a wire and apply them to find the actual resistance.PredictionI predict that, based on the reseach and the fact that the wire diameter and material remain constant (i.e, the same thickness and type of wire are always the same through each experiment), as the length of the wire increases the resistance will increase also.
So that if the wire length is doubled, the resistance should double as well.ExperimentPlanIn this experiment I plan to keep the metal constant and measure the volts and amps so I can calculate the resistance. I shall take a measurement every 10cm from 10cm up to 100cm so that there is a fair spread.EquipmentConstantan WireMeter RuleSticky TapePower PackVoltmeterAmp MeterResistorWiresCrocodile ClipsMethod1) Set up the circuit as shown in diagram above.2) Attach crocodile clips to wire at 100cm. Switch the circuit on and record the volts and amps displayed.
3) Do the same for lengths of 90cm, 80cm, 70cm, 60cm, 50cm, 40cm, 30cm, 20 and 10cm, recording the results along the way.4) Repeat the experiment twice more and record results.5) Work out the resistance of the wire by dividing the voltage by the current (amps) for each length.ResultsLength(cm)VoltsAmps10.0-0.51-0.1820.0-0.
08100.0-1.96-0.07Table For Experiment 1Length(cm)VoltsAmps10-0.52-0.1820-0.
08100-1.96-0.07Table For Experiment 2Length(cm)VoltsAmps10.0-0.
05Table For Experiment 3Length(cm)VoltsAmpsResistance (V/I)10.0-0.61-0.183.3920.0-0.93-0.
0631.83Average Results TableAnalysisThe evidence shows that voltage and current are important factors to consider when investigating resistance of a wire. As the length increases the voltage increases and the current decreases.From the evidence shown in the graph the length of wire is directly proportional to the resistance given.
This means as the length of wire increases the resistances is greater.ConclusionThe conclusion I have come to is that by increasing the length of the wire you increase the resistance in the wire.My prediction was correct; the resistance did change in proportion to the length.This is because as the length of the wire increased the electrons that made up the current had to travel through more of the fixed particles in the wire causing more collisions and therefore a higher resistance. If a length of a wire contains a certain number of atoms when that length is increased the number of atoms will also increase.
In this diagram the first wire is half the length of the wire below and so has half the number of atoms, this means that the electrons will collide with the atoms half the amount of times.Also if the length of the wire was trebled or quadrupled then the resistance would also treble or quadruple.EvaluationOverall in my opinion the investigation went well. The experiment was conducted efficiently with the results collected well.There were some anomalies and at first I found them inexplicable, until I furthered my research. There I discovered that there was a basic fact that I had overlooked in the first place.
Ohm’s Law states that: “Provided that the temperature remains constant, the ratio of potential difference (p.d.) across the ends of a conductor (R) to the current (I) flowing in that conductor will also be constant”.I could not guarantee that the temperature remained constant. From my research I know that temperature is another factor of resistance and therefore will have a direct effect on it.
The temperature fluctuations in the classroom could explain some of the abnormal experiment results however there are more explanations.Most errors in our experiment were encountered in the measuring of the wire. This is because it simply was not very practical to hold a piece of wire straight, whilst holding it next to a ruler and then trying to accurately fix crocodile clips to the right part on the wire. Also I do not feel that the crocodile clips were always fixed securely to the wire with a good connection. This also meant that they were easy to move about on the wire changing the length of it. Errors rarely occurred in the reading of the voltage and current. It was just in the preparation area that they did occur. Another example of this is the wire was never totally straight when we started the experiment, which may also affect the resistance of it.
To improve the investigations I could have studied the effect of applying more constant factors.For example, I could have kept the current at 0.10 amps. I would have chosen this value so that I would be sure that this was the exact number, as opposed to using something like 0.01, which could also have more numbers after the second decimal place (e.g, 0.017).I could use a different material instead of the metal alloy Constantan that was used, for example copper or iron, or even some none metallic conductor.I could investigate how any of the other factors affect resistance.The evidence collected, although there were some anomalies, was enough to support my prediction and the experiment did prove that the length is directly proportional to the resistance.I know this because as the length increased the resistance increased also, proving my prediction correct.