Where I is current in amps, V is the applied voltage in volts, and R is resistance in ohm
Key terms: Voltage The amount of energy per unit charge. Measured using a voltmeter. Recorded in volts (V)
Current The rate of flow of charge. Measured using an ammeter. Recorded in amps (A)
Ohms The current in a circuit is directly proportional to the applied voltage and inversely proportional to the resistance of the circuit. http://www.the12volt.com/ohm/ohmslaw.asp
Key Variables: http://www.regentsprep.org/Regents/physics/phys03/bresist/default.htm The resistance of a wire depends on certain factors. Some of these variables are listed below:
· Length of wire - discussed in ‘Justification of hypotheses’
· Diameter or thickness of wire - If the wires 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 fewer collisions. The electrons move at the same speed no matter what the current, however there are more electrons if the diameter is wider, thus resulting in the resistance to be lower.
· Temperature at which wire is kept - The hotter the wire, the more resistance is produced, thus affecting the resistance. This is because the electrons in a hotter wire have more energy, thus moving faster across the wire. This high amount of energy means that the resistance is higher.
· The material of which wire is made out of - Electrons find it easier to pass through some materials than others, consequently affecting the resistance. Some materials are better conductors than others and offer less resistance to the flow of charge.
All these factors will have to be kept constant except the length of the wire whilst doing the experiment to ensure that the investigation is a fair test.
Fair Test: In order to keep this a fair test, I will take repeat readings. Not only will this make it a fair test, I will get more accurate results. I will also record my final results based on averages, as this gives a clearer and fairer set of results. I will also keep the conditions of the experiment to a certain extent the same, as differences in temperature may affect the resistance.
Apparatus: I will need the following equipment:
· 1 Metal wire · 1 Power Pack
· 1 Meter Rule · Wires
· 5 Crocodile Clips · 1 Voltmeter Shunt
· 1 Ammeter · 1 Ammeter Shunt
· 1 Voltmeter
Diagram:
Method: In order to complete this experiment, the length of a wire will be changed then its resistance recorded. This will be done a number of times, in order to make the investigation a fair test. The results of a minimum of four different readings will be collected, as repeating the experiment makes it more accurate and reliable. The following steps will be completed: · Firstly, the circuit will be set in series, with the voltmeter in parallel.
· Secondly, the current and voltage will be recorded with the wire at 5cm. With the wire at this length, the results will be recorded four different times, so that the experiment is fair.
· Next, the crocodile clip will be moved up in intervals of 5cm, and each time the result recorded four times.
· The results will be recorded from 5cm to 35cm, each one four different times. Once a result is recorded, the power pack must be switched off before recording the next result. This is to reduce inaccuracies and to make the test a fair one.
I have decided to investigate how the length of a wire affects its resistance because other factors such as temperature are hard to control or vary. There are not a large enough range of materials to investigate how materials affect the resistance of a wire. The way in which the length of a wire affects the resistance is an efficient experiment to do. A graph can be plotted easily and there is a large range of results.
Preliminary Results: An experiment was carried out and the following results were recorded into a graph.
Graph of Results:
Unfair Result:
The results in this experiment show some anomalous results. This could be the result of too fast or too slow reactions in switching the power pack off and on. This could lead to an unfair outcome in results, and thus making the results unreliable. Also, I may not have let the wire cool down before taking the next reading, and this may have altered the results.
In order to overcome faults like this in my experiment I will make sure that the power pack in every reading is turned on and off during the same time period. I will also try and keep the temperature the same throughout.
Results Table:
The following is a blank table in which my results will be recorded.
The results will be recorded in a table identical to the one above. It is easy to comprehend the results, as they are laid out in different columns, and each different result is written in rows. The average results have also been worked out, as this makes drawing the graph a whole lot easier. It saves us from drawing four different graphs and them comparing them, therefore it is easy to just draw one graph.
Table of Results:
This table shows my results for the experiment. I have drawn a graph to illustrate these results:
Graph of results:
The following graph shows the resistance of the different lengths of a wire. Because of the fact that there are four different sets of results each time, the average result will have to be worked out. This is a more reliable and efficient way of drawing graphs if there are a number of different results.
Observations:
Having studied the graph, I am able to conclude that my hypothesis is correct:
‘The longer the wire in the circuit, the higher the resistance will be.’
Conclusion
With all my results, graphs and research I have concluded that my hypothesis has been proven to be correct. I have found out that the longer the wire, the larger its resistance. Also, I can safely say that, in this case, Ohms Law is correct, as the resistance increased by 0.1 every time, therefore being directly proportional to the length of the wire.
Evaluation:
Looking back at this experiment, I can say that enough data was collected to reach definite conclusions. As the graph shows, the resistance increased as the length of the wire increased.
To make this test a fair one, I took many things into account:
· I kept the current at 2V DC to ensure that the wire did not overheat, in which the reading that I would take would be inaccurate. To ensure that I had my results to perfection I took all my readings to two decimal places. I never rounded up.
· I also made sure I used the same wire and not a different one, incase this may change the results slightly.
· Another thing I did to make sure this was a fair test was to switch the power pack on and off very quickly, so that the wire didn’t get too hot and affect the results.
Therefore, none of my results appeared to be anomalous.
To improve my experiment, I could have taken more care over the temperature at which the wire was kept. To do this I would have to switch the power pack on and off at exactly the same time and also to wait for the wire to cool for the same period of time.
If I were to do this experiment again, I would make sure that the preliminary results included no anomalous results, and this would enable to compare the two experiments together. . From this I could be able to compare the similarities of the two experiments rather than differences. It would also be easier for me to draw quick conclusions.
Overall, I feel that I have completed this experiment quite well. My results are reliable and accurate and so I can conclude that the longer the wire, the larger its resistance.
Bibliography:
http://www.the12volt.com/ohm/ohmslaw.asp
http://www.regentsprep.org/Regents/physics/phys03/bresist/default.htm
Class work book & Text book.