By increasing the thickness of the wire, I predict that the resistance will decrease. I believe this because as the thickness is doubled the electrons will have more space to move freely and therefore having fewer collisions with the metal atoms.
Research and scientific knowledge
Resistance
It is a property of a substance that restricts the flow of electricity through it; it is 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 like; it's temperature, dimensions and thermal properties, degree of impurity, the nature and state of the illumination of a surface, and the frequency and the size of the current. The SI unit of a resistance is the ohm.
Ohm
SI unit (Ω) of electrical resistant that restricts the flow of electrons through it and is worked out by the V=IR rule meaning Resistance= Voltage
Information from Hutchison Encyclopaedia, Physics for You and GCSE Bitesize-Physics.
Method:
- Set the circuit as shown above, the ammeter in series and the voltmeter in parallel.
- Set the voltage quite low, like four because you don’t want the wire to get too hot, as it would effect the resistance. This also happened in my preliminary experiment, at high voltages the wire became hot and the resistance increased, decreasing the reliability of my results
- First, using Nicrome wire cut it six times at different lengths. These lengths are 0.2m, 0.25m, 0.3m, 0.35m, 0.40m, 0.45m, 0.50m.
- I will repeat this twice for each length to make sure that there are no experimental mistakes.
- Then at each length measure and record the resistance by using ohms law.
- Next with Nicrome change the thickness. First connect 0.2m of Nicrome between the crocodile clips, and record (v) voltage (I) current to calculate (R) resistance.
- Then join another 0.2m Nicrome wire in parallel with it and repeat the above until you have five wires in parallel.
- Then repeat all the points above for a Constanton piece of wire.
- Finally then repeat the experiment to gain a more accurate average.
Experiment 1:
Results for different lengths For Nicrome and Constanton
Nicrome
Constanon
Experiment 2:
Results for different thickness for Nicrome and Constanton
Constanton
Nicrome
Analysis
After analysing my results I have come to the conclusion that for both Nicrome and Constantion the resistance got larger as the length increased. I believe this was because as we doubled the length, we doubled the collisions between the electrons and the metal atoms, making it twice as hard for the electrons to go through and therefore making the resistance larger. Using my scientific knowledge I found out metals conduct electricity because the atoms in them do not hold on to their electrons very well, and so creating free electrons, carrying a negative charge to jump along the line of atoms in a wire. Resistance is caused when these electrons flowing towards the positive terminal have to 'jumps' atoms. So if we double the length of a wire, the number of atoms in the wire doubles, thus the number of jumps double. So twice the amount of energy is required: There are twice as many jumps if the wire is twice as long and that’s why with my results as I doubled the length so did the resistance. Also as the wire width increased the voltage tended to go down and the current went up but some of these vary due to some inaccuracies.
Analysing my graph for experiment 1, a straight line through the origin can be seen. This means R, is directly proportional to L. Thus for example, if the length is 40cm, and the resistance is 2, then if the length is doubled to 80cm, the resistance also doubles to 4.
After analysing my results from experiment 2 one can see that for both Nicrome and Constantion the resistance got smaller as we doubled the thickness. The thinner the wire is, the fewer 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. I predicted that by doubling the thickness it would equal half the resistance and predicted that they were inversely proportional to each other.
Resistance = 1/Area.
This can be explained using the formula
R = V/I
Where there is 2X the current, and the voltage is the same, therefore R will halve. I did some research and in a book called 'Ordinary Level Physics' By A. F. Abbott, it says 'That doubling the area will therefore halve the resistance'- in other words the resistance of a wire is inversely proportional to its area, proving my prediction correct.
However my graph results showed that this is not true because they produced a curve pattern. One theory I have to explain this is to do with the flow of free electrons. As the wire gets thicker there is more metal and therefore more free electrons, so resistance decreases. However the voltage is constant so therefore it is the amount of energy given to each electron, so once the optimum energy per electron is reached it increases. Then the thickness does not have much affect. In conclusion it can be said that as you double the thickness of the wire there will be more space for the electrons and metal atoms and therefore fewer collisions happening between the two, making it easier for the electrons to pass through decreasing resistance. However there is an optimum amount where the resistance will decrease the most.
My results for experiment one are quite accurate and have proven my predictions correct. My results for experiment 2 were partly correct and did prove some of my predictions correct.
Evaluation
I believe both my experiments were accurate because the points on my graph were very close to my line of best fit and also because I took two readings of my results for resistance, current and voltage and then worked out an average. In both my experiments there were no real anomalies or strange results and backed up my prediction well.
I believe the method was a good and accurate one and supported both my experiments well. I have managed to achieve good, reliable results as I worked out an average for both experiments and drew a line of best fit for both graphs. I also believe my results were good enough to support a firm conclusion as they also agreed with my prediction and scientific knowledge.
For further work relevant to this experiment we could investigate the effect of other variables such as the voltage and temperature of the wire and its effect on resistance. This would help us have a better understanding of how resistance varies under different conditions.
To further improve this investigation I would use digital ammeters and voltmeters, to achieve a much more accurate method of measurement. It would also be a good idea to take a wider range of readings so that one can have a much more accurate average to work with.
I have enjoyed doing this investigation and has taught me a lot more knowledge on resistance and its factors.
By Zahid Siddique 10E
