10 0.270.190.130.100.07 0.100.060.050.030.02 0.370.320.380.310.29 0.33
Main Experiment
Prediction
I predict that if the length increases then the resistance will also increase in proportional to the length. I think this because the longer the wire the more atoms and so the more likely the electrons are going to collide with the atoms. Therefore, 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 directly proportional to the resistance If the length of the wire is only half the length of the wire on the same type of wire, there should be half the number of collisions between the electrons and the atoms.
If the wire is twice as long, there should be twice the number of atoms, resulting in twice as many collisions and a predicted doubling of the resistance.
Safety
Handle the power supply carefully.
I am going to only use a voltage of four volts so the wire will not burn.
Be careful when touching the wire, as it may be hot.
Start on the lowest current, so the wire then will not melt or burn instantly.
Be careful when the wire is connected, as it will get hot.
Be careful when cutting the wire.
Make sure the mains to the power supply is switched off when removing the wire from the circuit to be measured.
Apparatus
Power Supply, Ammeter, Voltmeter, Just over 100cm of E26 Wire, Meter Rule, Two Crocodile Clips, Connecting Wires.
Factors which must stay constant to keep the experiment a fair test
The power supply must stay on 4V, The wire must be the same thickness, The surrounding temperature must be constant, The equipment should be kept the same, The edge of the crocodile clips should be at the edges measured length.
The Variable factor
The factor that I am going to vary is the length of the E26 wire.
Circuit diagram
Method
The circuit was set up as shown above. A table was drawn out and the results were recorded. To improve the accuracy, compared to my preliminary results for my main
Experiment, I have decided to set up the circuit with the metre rule selotaped to the bench. This will make it easier and more precise as I will not have to keep on holding the wire then putting the crocodile clips on. I have chosen to use a meter ruler because the lengths that I will be measuring are to big for a smaller ruler and the meter ruler can be accurate to +1mm. Make sure that the metre rule is actually one metre long and not one or two centimetres shorter. Next, move the crocodile clips down five centimetres rather than ten (as done in preliminary) each time to record the results. Use the E26 wire as it will also be easier to measure any change in resistance. To collect the data for my graph I have chosen to take a range 20 of lengths. I have chosen a range of 20 as to plot an accurate graph, I will need at 20 points to mark on the graph if I want to make precise and reliable results, to see if there are any patterns and trends. I have also chosen to take five repeats at each length and then take an average, to get reliable results. The lengths that I have chosen are as follows: 100cm, 95cm, 90cm, 85cm and going down in fives to 10cm length of wire. I have chosen these lengths because they are easily measured by the meter ruler and give a good range of results.
As my preliminary results start to show a pattern in the readings (Resistance is directly proportional to length) to expand on my experiment and to see if this pattern continues, I am going to try the above lengths.
Results
To calculate the resistance of the wire, I shall use the equation below.
RESISTANCE = VOLTS/AMPS
Below is a results table with the results that I collected from my main experiment.
1 2 3 4 5
Length (cm) Volts (V) Amps (A) Resistance (Ohms)R=V/I Average Resistance (Ohms)
100 0.330.200.220.180.17 0.100.060.070.060.05 3.333.333.143.003.40 3.24
95 0.710.520.350.320.23 0.230.180.110.100.07 3.092.893.183.203.28 3.12
90 0.700.460.340.270.22 0.260.150.110.100.07 2.793.063.092.703.14 2.94
85 0.650.420.330.270. 26 0.270.140.130.110.08 2.403.002.542.453.25 2.78
80 0.700.540.390.280. 21 0.290.230.160.120.09 2.413.352.432.332.33 2.56
75 0.550.340.260.210.19 0.250.160.120.090.08 2.222.132.172.223.37 2.
70 0.510.330.230.180. 17 0.240.160.100.080.06 2.132.122.132.242.80 2.25
65 0.440.270.210.200. 18 0.220.140.100.110.09 2.001.942.101.812.00 2.11
60 0.220.130.230.200.07 0.110.200.120.090.10 2.001.531.922.011.28 1.75
55 0.330.280.250.240.19 0.200.170.140.120.11 1.651.651.792.001.72 1.76
Length (cm) Volts (V) Amps (A) Resistance (Ohms, ) Average Resistance (Ohms, )
50 0.290.150.240.120.11 0.190.090.130.080.07 1.531.671.841.501.57 1.61
45 0.610.370.280.180.17 0.360.200.180.150.14 1.691.851.561.201.23 1.43
40 0.440.270.180.140.110.19 0.330.340.230.180.140.15 1.241.261.271.281.271.27 1.26
35 0.370.210.160.110.19 0.340.200.150.100.08 1.091.051.061.102.36 1.13
30 0.260.180.150.120.10 0.270.190.150.120.10 0.960.941.001.001.00 1.00
25 0.250.140.110.090.07 0.310.170.140.110.08 0.800.820.780.810.87 0.85
20 0.230.110.050.160.05 0.350.160.120.120.07 0.650.680.141.300.72 0.65
15 0.170.100.070.050.04 0.330.190.130.100.08 0.510.530.530.500.50 0.52
10 0.100.060.060.030.02 0.270.190.130.100.07 0.370.320.460.300.29 0.34
I have also drawn a graph to show how the average resistance changes with length
Analysis
In my prediction, I stated that:
If the length increases than the resistance will also increase in direct proportion to the length.
From my graph on the previous page, I can see that the resistance of the wire is directly proportional to the length of the wire. I know this because the Line of Best Fit is a straight line through the origin showing that if the length of the wire is increased then the resistance of the wire will also increase in proportion to each other. The line of best fit is a straight and it goes though (0,0) if there is no length, there is no resistance proving that the resistance of the wire is directly proportional to the length of the wire. This proves my prediction right. I can work out the gradient of this line by dividing the Resistance by the length. So, 1.75/55=0.0318
The length of the wire affects the resistance of the wire because the number of atoms in the wire increases or decreases as the length of the wire increases or decreases in proportion.
The resistance of a wire depends on the number of collisions the electrons have with the atoms of the material, so if there is a larger number of atoms there winl be a larger number of collisions that will increase the resistance of the wire. If a length of a wire contains a certain number of atoms when that length is increased, the number of atoms will also increase
If the wire is half the length of a certain wire, it would have has half the number of atoms, this means that the electrons will collide with the atoms half the amount of times. In addition, if the length of the wire was trebled or quadrupled, then the resistance would also treble or quadruple. This is indicated on my graph, with the length being 100cm and the resistance being 3.25 Ohms. This in theory would mean that at 50cm there would be a resistance of 1.63 Ohms. From the graph it is easy to tell that the theory is correct and therefore my results reliable. From my results table and graph, I can see that my results that I collected are quite reliable and accurate. I know this because my results table shows a few, individual anomalous results; the anomalous results are at lengths 95cm and 100cm. All the other points are extremely close to the line indicating that my results are accurate
I think that my results are suitable to confirm my prediction and support a conclusion. I know this because outside resources (Textbooks and Britannica) say that ‘the length increases in direct proportion to the resistance.´
Evaluation
In the Analysis and the graph I have shown two main anomalous points, this means that there must have been a slight error in my experiment. As the wire, length is bigger at these points I found it harder to stretch it out and consequently, measure it accurately. Although the graph is overall accurate and the results precise it is easy to see, the anomalous averages plotted because they do not all lie along the same best-fit line. The graph shows that my results are reliable as there are only two main anomalous points, (which are easily accounted for) to improve the reliability of my results, I could do more repeats in doing this my average would be more reliable. As I increased the wire length, the wire became hotter and gave off heat. This could explain why the anomalous results are at the top of my graph, 100cm and 95cm. I think one of the reasons why my experiment is quite accurate is because I tried to measure the wire as accurately as possible. The metre rule was selotaped onto the workbench. The wire was stretched until it was nearly in a straight line so a bit was overlapping at each end. As the metre rule was curved and worn down at the corners it was slightly hard to see where 0cm was. Finally, the inside edge of the crocodile clips were placed at the appropriate point. I still however would like to make the measuring more accurate
During my experiment, I have noticed several modifications I could make to improve on the Investigation if I was to repeat it.
The first of these modifications would be the circuit that I would use. To be more accurate with my results I would place the Metre rule directly under the wire, so therefore it would be measured easier and therefore making the lengths more precise.
Instead of connecting the voltmeter to the main circuit, I would connect it to the wire that is being tested. I would do this so that the voltmeter is measuring the voltage of just the wire being tested and not the wires of the main circuit as well.
To also improve on my results I could use a new or higher quality digital voltmeter. The next modification I would make would be to use pointers instead of crocodile clips to attach to the wire; I would do this because pointers would be more accurate. The pointers would be more accurate because the tips have a much smaller area than the crocodile clips giving a more accurate measurement of the length of wire. I would also use a newer metre rule. The graph shows that my results are reliable as there are only two anomalous points, to improve the reliability of my results, I could also have repeated the same lengths of wire more times. Although the wire is an E26 wire, the thickness of it may vary by a small amount and maybe helping to cause the anomalous results. Sometimes the ammeters flicked between a decimal point, I maybe could have thought it was the wrong number and therefore would have ended up with the wrong average resistance. In the experiment, I did not control the room temperature but instead just assumed it was keep constant throughout my experiment; this could have made the wire get hotter and therefore making my experiment not as accurate. In future experiments I would control this variable factor and make it a constant factor. I would do this, as it would be an unfair test if there were two known variables.
As well as making these modifications, I could also expand on my investigation by testing the same wire but different widths of that wire. I would do this if I had more time to complete it. I think the circuit and method used was quite suitable although I would make the modifications above to improve my results. If I did this experiment again I would defiantly use top quality equipment, I would probably control the temperature and use pointers instead of crocodile clips. After changing those few things, there is not really much difference to how I would do the experiment again.
Plan
From www.essaybank.co.uk
Investigating the Resistance Of A Wire When The Diameter Of
The wire is altered.
Plan
Introduction
The resistance of a wire depends on certain factors. Some of these variables are listed below:
· Length of wire
· Diameter or thickness of wire
· Temperature at which wire is kept
· The material of which wire is made out of.
· The potential difference or voltage.
· Humidity
· Cross sectional area.
· Voltage across circuit
All these factors will have to be kept constant except the diameter of the wire whilst doing the experiment to ensure that the investigation is a fair test.
I have decided to investigate how the diameter of a wire affects its resistance because other factors such as temperature are hard to control or vary. There is not a large enough range of materials to investigate how materials affect the resistance of a wire. The way in which the diameter of a wire affects the resistance is an efficient experiment to do. A graph can be plotted easily, there is a large range of results and the results can be recorded easily.
Variables
The investigation is to investigate the resistance when the diameter has changed. In order for the investigation to be a fair test, all other factors or variables should be kept constant. The investigation has to be done in a fair manor otherwise the results would be inaccurate and the conclusion would be incorrect. The variables, which must be kept constant, are:
1) Temperature When the temperature of a metal increases the resistance of that metal increases. This is because when the temperature increases the atoms of the metal vibrate more vigoursly because of the increase in energy. This means that the electrons have more difficulty getting through the wire as they collide with the atoms which are in their pathway. This increases the amount of collisions therefore there is more resistance. However it is hard to keep the temperature exactly the same as the room temperature might change from day to day. It is essential to use a low voltage because it means a low current that will not heat up the wires. If a high voltage is used the energy would be in form of heat which would make the experiment unfair. The investigation will be done at room temperature. The temperature cannot be investigated because it is hard to control the range of temperature needed without the correct apparatus.
Research
All materials, solid, liquid or gases are made up of atoms. The atoms themselves consist of a central bit, called the nucleus, made up of particles called protons (which have a +ve electrical charge) and neutrons (which have no charge) Orbiting around the nucleus are electrons which are very tiny and have a -ve electrical charge. One can think of the electrons orbiting in layers like the rings of an onion, and it's the ones in the very outside layer, the outer shell, that are the most important when thinking about conduction.
In metals, the outermost electrons are held only very weakly to the atom and often wander away from it and go to the nearby atom or one a bit further away. These wandering electrons are called conduction electronsand the more of these there are, for a given volume of metal, the better the metal will be as a conductor of electricity. When you connect a battery across a wire, one end becomes +ve and attracts the conduction electrons, which drift towards that end of the wire. But the electrons have obstacles to face because the metal atoms are jiggling about because of their thermal energy and so the electrons collide with them and are knocked all over. It’s this difficulty that the electrons have in moving along the wire that we call resistance.
Resistance involves collisions of the 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. Without resistance, the amount from even one 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 and the symbol is: The higher 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. Wires are always made out of copper because copper has a low resistance and therefore it is a good conductor. 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. To make the experiment reliable, all apparatus must be checked to see if it is functioning properly and is giving a true reading. This will partly avoid systematic error. Another way to make the experiment reliable is to use two methods: to do the investigation in two different ways to measure the resistance when the diameters are changed. If one method contains systematic error or is very inaccurate, the other method will be used to recognise that.
