Method,
- Setup all equipment accurately; making sure that there is a complete circuit.
- Draw up a table with appropriate headings, for the ability to record results quickly and efficiently.
- Attach one crocodile clip to the wire on the metre stick at the point marked 0cm.
- Attach the second crocodile clip on the 10cm mark on the wire.
- Point 4 will increase by 10cm after each recorded result until the experiment has reached 100cm.
- Turn on the power pack.
- The power pack should be set to 4 volts.
- The readings on the ammeter may be fluttering, if this is so record the modal result that you can see on the ammeter.
- Place these results into your drawn out graph
- Carry on the experiment with the next 10cm.
- When this has been completed, repeat steps 3- 10, twice more in order to get very accurate results and be able to find a respectable average to draw the graph by.
Keeping The Experiment Safe,
This is not a dangerous experiment however you must always use electricity with care. The following is the two main factors to ensure safety in this experiment:
The Current – I will make sure that I have complete control over the current and keep the current reasonably low. I will ensure this by concentrating solely on the work in hand.
Keeping water away from electricity– It is vital when using electricity I stick to the correct precautions, and keeping my hands and immediate surroundings dry is common sense when dealing with electricity.
Results,
The tables show my results for my three experiments carried out. I worked with Amandeep Gill to record these:
Experiment (a),
Experiment (b),
Experiment (c),
Averages of all 3 Experiments = (a)+(b)+(c)
3
Analysis,
From the graph we can see that the line of best fit fits very accurately but above all else it is clear that as the length of the wire increases so does the resistance of it. Another perhaps more significant observation is that the increase is constant.
We can see now that as the length of the wire increases so will the resistance of the wire also. I also think that the rate at which the resistance increases will be determined by the length of the wire. Resistance is the property that changes electrical energy into heat energy. We must note here that in every conductor there are free electrons in the outer shell of the atom and as we know, metals are conductors and each have forms with similar arrangements.
As a result of this certain structure in all atoms which are conductive, the outer electrons can move about freely even in a solid. When there is a difference across a metal, the free electrons place themselves in lines moving in the same direction which makes up an electrical current. Resistance is found once the electrons collide with other particles in the metal. As the resistance of the material increases, so must the force required to drive an equal amount of current. Resistance in ohms(R) is equal to the electromotive force in volts (V), divided by the current in amperes (I). This is Ohm’s law. As the length of the wire is increased the numbers of collisions the current carrying electrons make with other fixed particles also increases and so the value for the resistance of the wire becomes higher. Resistance in ohms (R) equals the resistively of the wire in ohm-meters (ñ) multiplied by the length in meters (l), divided by the cross sectional area, in square meters (A).
Overall, the resistance can be worked out using these particular formulae:
Resistance = resistively of the wire x length
Cross sectional area
Resistance= electromotive force
Current
Symbolized Formulae:
R= ñ x l
A
R= V
I
Evaluation,
I feel that overall our results were particularly accurate. This is can be seen when observing the graph, which shows a straight line of best fit with all of the points apart from one being very close to or on that line. The only point that was not that close to the line was a slight abnormality, but it was very small and did not affect the overall gradient of the line.
The accuracy for this experiment is, as I’ve been informed in theory, ± 15.7%, but as you can see this is not true from looking at the graph. One reason for this could be the temperature of the wire; it was not necessarily room temperature when we conducted the experiment. It may have been in sunlight and be previously heated naturally. The material of wire may not be as pure as it should have been also. Perhaps the main reason for the inaccuracy was probably due to the equipment that we used being inaccurate. However this did not stop us from being able to see a trend, because the equipment would have been out by the same amount each time and so there would have been a constant error. So the trends that I predicted were still shown.
Most errors in our experiment were most likely encountered in the measuring of the wire. This is because it becomes difficult to place the crocodile clips exactly on the point on the metre stick. The wire was also raised off of the surface of the stick so this could have meant that the measurements may have been read incorrectly. Also I do not feel that the crocodile clips were always fixed tightly to the wire with a solid connection. This also meant that they could easily move about on the wire and so changing the length of it. Little to no mistakes/errors occurred whilst doing the setting of the current and the reading of the voltage. It was just in the preparation that the errors occurred. Another example of this is the wire was never completely straight when I started the experiment, which can also, affect the resistance of it.
I do not think that doing any more results in our experiment would have made it any more accurate. I do, however, think that another method is the only way to improve the practicality and accuracy of the experiment, perhaps if I had used a solid bar that was unable to bend instead of the wire.
