Electric current is the movement of electrons through a conductor. In this experiment a metal wire (Nichrome will be the conductor). So when resistance is high, conductivity is low. Metals such as Nichrome conduct electricity well because the atoms in them do not hold on to their electrons very well. Free electrons are created, which carry a negative charge, to ¡¥jump¡¦ along the lines of atoms in a wire which are in a lattice structure. Resistance is when these electrons which flow towards the positive collide with other atoms, they transfer some of their kinetic energy. This transfer on collision is what causes resistance. So, if we double the length of a wire, the number of atoms in the wire doubles. This increases the number of collisions and energy transferred twice, so twice the amount of energy is required. This means the resistance is doubled.
My graph should show that the length is directly proportional to the resistance.
Predicted graph :
When measuring resistance in the length of a wire the independent variable is the length of the wire and the dependant variable is the resistance. The factors that I will keep the same during this experiment are :
"h The temperature
"h The thickness of the wire
"h The type of wire
Safety Precautions :
There are not many safety precautions that need to be taken into consideration, in this experiment. The main two I can think of are stated below :
"h Do not carry out the experiment in wet areas, as water is a very good conductor, and thus could be very dangerous.
"h Do not touch the wire when the multimeter is switched on, because the current would heat up the wire.
Apparatus :
"h Multi-meter
"h Nichrome wire
"h Meter Ruler
"h Crocodile Clips
"h Sellotape
"h Connection Lead
I set up my experiment as shown above.
I started the experiment by sellotaping the Nichrome Wire (over 1 meter long) to the meter ruler. Then the multimeter was switched on which was connected to the Nichrome wire via the crocodile clips. The resistance was then recorded down for various lengths ranging from 0 ¡V 100cm. I then plotted these results on a graph.
To collect the data for my graph I had chosen to take a range of 10 lengths. I had chosen a range of 10 as to plot an accurate graph I will need at least 10 points to mark on the graph. The lengths that I had chosen were as follows: 10cm, 20cm , 30cm ,40 cm, 50cm, 60cm, 70cm, 80cm, 90cm, 100cm. I have chosen these lengths because they are easily measured by the meter ruler and give a good range of results. Voltage is not used in this experiment as it will heat up the wire and thus affect the results.
I will repeat my results twice
Results :
Length (cm) Resistance (ohms )
10 001
20 002
30 003
40 004
50 005
60 006
70 007
80 008
90 009
100 010
Analysis and Conclusion :
The graph is a straight line through the origin, which means R is directly proportional to L. This means that if the length is 40cm, and resistance is 4ohms, then if length is doubled to 80cm, resistance also doubles to 8ohms.
This is because of the scientific idea, stated in the planning that if you double length, you double the number of atoms in it, so doubling the number of electron 'jumps', which causes resistance: The results support my predictions well, the results turned out the way I had expected, they match the predicted line well. I had predicted a straight line through the origin, which means R is directly proportional to L.
So, this effectively means that if the wire was trebled or quadrupled then the resistance would also treble or quadruple.
Evaluation :
From my graph I can see that my results that I collected are very reliable. I know this because my graph does not show any individual anomalous results. I can see on the graph that none of the results plotted are anomalous because all the points lie along the same straight line.
When I was measuring the lengths of the Nichrome wire, my measurements might have been slightly inaccurate as the rulers used might not have been exact, and it was difficult to get an accurate reading of length by eye, as the wire was not completely straight, so it may have been of different thicknesses throughout the length. This would have contributed as a slight error in my results. As this factor probably only made a slight difference, it did not affect my results.
The crocodile clips and the connecting leads could have affected the fairness of the experiment. They are a different type of metal from the Nichrome wire and may have different properties and therefore different resistance. Therefore the resistance of the Nichrome wire showed up on the multimeter was slightly more than it actually was. To solve this problem, I would have finded out the resistance of the connecting leads and crocodile clips before each experiment and minus it from the overall resistance of the Nichrome wire plus the connecting leads plus the crocodile clips.
c = a - b
a = overall resistance of Nichrome wire, crocodile clips and connecting leads
b = overall resistance of crocodile clips and connecting leads
c = resistance of Nichrome wire
To make my experiment possibly more accurate I could have got 3 sets of results and found an average but this would be too time consuming.
I don¡¦t think I could really improve on the way the experiment was done because my results were very accurate, as I had no anomalous results.
I also found that the experiment was quite easy to set up, as it was simple and uncomplicated.
Further experiments I could do related to ¡¥the resistance in a wire¡¦, would be to see whether the following factors would make a difference in the resistance of a wire : ( I have made a prediction for each factor from my own scientific knowledge on how I think the resistance would change in a wire for that particular factor )
"h Wire width :
I think that if the wire width is increased the resistance will decrease. This is because of the increase in the space for the electrons to travel through. Due to this increased space between the atoms there should be less collisions.
"h Temperature :
I think that if the wire is heated up the atoms in the wire will start to vibrate because of their increase in energy. This causes more collisions between the electrons and the atoms as the atoms are moving into the path of the electrons. This increase in collisions means that there will be an increase in resistance.
"h Material :
I think that the type of material of the wire will affect the amount of free electrons, which are able to flow through that wire. This is because the number of electrons depends on the amount of electrons in the outer energy 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 a 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 and the resistance will increase.
