Prediction:
I believe that:
The greater the length of the wire the greater the resistance as there are more atoms and therefore there is a greater opportunity for electrons to collide and hence the greater resistance. If a wires length is longer then the electrons will have to gather together for a greater period of time to pass through a wire then they do in order to pass through a short wire that’s why there is greater resistance in a longer wire. So if the length is doubled the resistance should also double. This is because if the length is doubled the number of atoms will also double resulting in twice the number of collisions slowing the electrons down and increasing the resistance. My graph should show that the length is proportional to the resistance when I draw up my results in a line graph.
The thicker the wire the less resistance there will be as there will be an increase of area for the electrons to travel through, so the atoms will collide less which will lead to a low resistance because there wont be as many collisions.
The type of material will affect the amount of free electrons able to pass through a wire. The number of electrons depends on the number of electrons in the outer shell of the atoms, so if there are more or larger atoms then there must be more electrons available. If the material has a high number of atoms there will be high numbers of electrons causing lower resistance because of the increase in the number of electrons. Also if the atoms in the material are closely packed then the electrons will have more frequent collisions
I think all these factors will play a role in how the resistance varies. If two factors are to remain constant such as the thickness of the wire and the materials they are going to be in this investigation, then the varying length will still have a major affect on the resistance of the wire. I feel that the greater resistance will be if the length of wire is greater and I feel this will be in proportion to the resistance as Ohms law states this.
Scientific Background:
All materials, solid, liquid or gases are made up of atoms. The atoms themselves consist of a central area, which is called the nucleus, this is made up of particles named protons (which have a positive electrical charge) and neutrons (which have no charge). Circling around the nucleus are electrons that are small and have a negative electrical charge.
In metals, the outer shell of electrons are held weakly to the atom and an move away from the atom and go to another nearby atom or approach another one a bit further away. These moving electrons are named conduction electrons and the more of these there are, for a given volume of metal, the better the metal will be as a conductor of electricity. When a battery is connected across a wire, one end becomes positive and attracts the conduction electrons, which drift towards this positive end of the wire. The electrons have obstacles to face because the metal atoms are wobbling about because of their thermal energy and so the electrons collide with them and are knocked into different directions. This difficulty that the electrons face in moving through the wire we call resistance.
Resistance is made up of collisions of current-carrying charged particles with fixed particles that make up the structure of the conductors. A resistor is a material that makes it hard for electrons to go through a circuit so slows the process down. Without resistance, the amount from even a single volt would be infinite. Resistance occurs when electrons travelling along the wire collide with the atoms of the wire. The unit of resistance is Ohms
The greater the resistance, the lower the current. If there is high resistance, to get the same current a higher voltage will be needed to provide an extra push for the electricity. Some metals have less resistance than others this depends upon material, diameter and cross-sectional area. Wires are mostly made out of copper because copper has a low resistance and therefore it is a good conductor of electricity. The length and width of a wire also has an effect. In this investigation I will investigate how the diameter of a wire will affect the resistance in the circuit as well as the length.
Apparatus:
- Ammeter
- Voltmeter
- 0.23 mm Constantin Wire
- Meter Rule
- 2 Crocodile Clips
- 6 Connecting wires
- Power Supply.
Circuit Diagram for the investigation:
Main Method:
- Firstly I will set up the apparatus as shown in the circuit diagram above I will make sure the ammeter will be connected in series and the voltmeter will be connected in parallel across the circuit.
- The battery pack will then be placed on two volts.
- The wire will be attached onto the circuit with crocodile clips. With the first length at 55cm. The power supply will then be switched on and measurements for the volts and amps will be noted in a table.
- The length will be increased by 5cm and more measurements are going to be taken, this process will continue until the length of 90cm has been obtained. At each length the amount of volts and amps will be noted so later the resistance could be worked out by doing:
Volts/amps = resistance
- The results are going to be processed into a result table with the resistance for each length having been worked out. These results will be plotted into a line graph with a line of best fit and later the investigation is going to be analysed and evaluated.
Fair test:
In this experiment we are only changing one factor – the length of the wire, the factors that we are going to keep the same are as follows:
We must keep the surrounding room temperature the same or the particles in the wire will move faster (if the temperature is increased) and this will therefore have an effect on the resistance.
The cross sectional area of the wire must be kept constant throughout as well. The material of the wire must also be kept the same as different materials have different conductivity. The last two factors will be kept the same by using the same wire all of the way through the experiment.
The current that we pass through the wire is to be kept the same, also. If this is changed the temperature of the wire might change in a way that is not constant this may cause anomalous results to occur.
Safety Precautions:
- Handle the power supply carefully only use with dry hands.
- Only use a voltage of 2 volts otherwise the wire may burn.
- Make sure you are careful when handling live wires.
- Start on the lowest current (therefore the lowest length in this case), so the wire then will not melt or burn instantly.
- Be careful when the wire is connected, as it may get hot.
Results:
These results are all to three decimal places. The resistance was calculated by using the formula:
Volts/amps = resistance.
Precision/accuracy:
To keep this experiment as accurate as possible I made sure, firstly, that the length of the wire was measured precisely from the inside edge of the crocodile clips also made certain the wire was straight when I did this. If the wire was not straight when I conducted the experiment, short circuits were possible to occur and bends and kinks in the wire would have effected the resistance. The reading I took of the voltage was done fairly promptly after the circuit was connected this is because when the current was put through the wire it could have got hot if the wire was left with current passing through it. I did not want the temperature to affect the resistance of the wire as this could have altered the precision of my results so therefore I tok the reading of the voltage as soon as I could.
Line graph for results with a line of best fit:
Analysis of results:
From my line graph I can see there are three anomalies and I have circled them. They are at the top of my line graph; their resistance is much more than the general trend shown from my line of best fit. There resistance may have increased as the temperature of the wire may have increased due to a warmer room and, or more heat actually building up on the wire.
My results show after every 10cm of wire the resistance increases approximately around one Ohm this occurs right up to the last reading that I took which was 90cm. I have also noted that there is a positive correlation in my results as the values all increase (y-values) as the length increases (x-axis).
From the line graph I have drawn it is obvious to note that the resistance line increases in proportion to the length of the wire. The significance of this is that the rates of increase remains constant this shows my results were fairly reliable as the resistance is in proportion to the voltage and this is what we know from Ohms law.
I think that from my results I can safely say that my prediction was correct. The resistance did change in proportion to the length as it increased by approximately one ohm every 10cm’s. 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. (Refer to scientific background)
Lamp Problem:
Th resistance needed to solve the lamp problem was 8 ohms and this can be calculated by doing the following equation:
Volts/amps = resistance
12/1= 12 Ohms
12- 4(The lamps resistance) = 8 Ohms
To find this resistance I have taken readings for current and volts for differing lengths of a 0.23mm-constantin wire and this can be seen on my line graph. From this graph I have calculated that the resistor needed to complete the circuit could possibly be of the material of constantin. With a diameter of 0.23mm and a length of 71cm as from my graph you can see that a resistance of 8 Ohms can only occur with this material and thickness on 71cm this is marked in red on my line graph.
Evaluation:
I believe that the investigation was fairly successful as I believe I achieved fairly precise and reliable results, which I was able to solve the lamp problem for. I can tell the results were fairly accurate as the most points were fairly close to the line of best fit. There was only really one slight anomaly, which I didn’t believe I needed to rectify as it was only mildly away from the line of best fit. I think this anomalous result was probably down to an increase of heat while doing the previous testing on other lengths. As this measurement was the last results to be tested it could have possibly gained in temperature and therefore its resistance was affected as temperature does affect the resistance because it gives electrons more energy to collide and hence the greater resistance because of the increase of collisions.
I think I could have made the investigation slightly more reliable by doing greater testing on results, as I believe I possibly did not take enough measurements. I could have gone from 5 cm of wire until 100cm not from 55cm-90cm however some of the shorter values maybe less than 25cm would get short-circuited. If I had increased the range I believe I would have got a more accurate line of best fit which I would have been able to pass more reliable comments on. Using different materials of wire and varying diameters could have also been an area which I could have possibly looked into if given more time on this investigation as if I had done this I could have looked at the different effects items have on resistance.
If I could have had a more precise measuring tool for measuring the wire this could have possibly given me more reliable results as I do not believe that the measurements of length I took were exact and this could have effected the resistance that I obtained for certain results. A way in which I could have tackled the problem was to place two points on the wire and then cut these points at either end using an electronic saw this would have given me more precise measurements. I also think the investigation could have been made more accurate if the wire was perfectly straight as the wires which I clipped onto the crocodile clips were often bent and had kinks in them, I feel this could have slightly altered the resistance. If I had a machine to straighten the wire then I think I would have possibly got more reliable results.
I believe that my investigation was successful as I did manage to complete all tasks set. I also feel that the results I took were sufficient to provide proof for my conclusions as I had enough results to draw a descent line graph from and then later analyse. I also was able to make relevant comments on my results and I was able to see patterns and trends, which lied in them.
By,
Mohammud Malik