The electrical resistance is increased because as more current is pushed though the filament it becomes hot and the atoms in the filament ‘jiggle’ about more because they have more energy. While the atoms are ‘jiggling’ more, there is less space for the current to pass through causing the electrical resistance to increase.
All materials are slightly resistant to electricity. Factors affecting the resistance are: Length, Voltage & Temperature and Surface Area.
Length: the longer the wire the more atoms.
Voltage: the more voltage the faster the current flows.
Voltage and temperature: temperature has and affect on the experiment. As the higher the voltage the hotter the wire gets. The higher the temperature the the more the atoms collide. This leads to a reduction in the output voltage, but this does not have much of an effect on the experiment.
Density/ surface area: this has a large effect on the resistance. A larger suface area, less resistance, this is because the atoms are not as tighly packed. But a small surface area has tightly packed atoms. This causes the electrons to rebound more.
Material: different materials have different amount of free electrons. The more electrons in the outer shell the lower the resistance. This is because there are more electrons for the current flow thorough. Also if the electrons are closer together the more collisions and the higher the resistance.
Equipment- For this experiment I am going to use:
-
Nickel Crome (∅ 0.71mm)
- Power pack
- Ammeter
- Voltmeter
- Ruler/ meter stick
- extra wire to make up the circuit
Safety-So as to be safe during the experiment we will all stand at all times and not be silly whilst carrying out the experiment. Also we should not be silly so as not to make the wrong observations or measurements.
Method-
- I will carefully collect all the required equipment needed for the experiment.
- Then I will sensibly set out the equipment.
- Sketch out an appropriate results table.
- I will then carry out the experiment, by passing the current through varying lengths of wire.
- And recording any findings.
- I have found out that the best way to record my results is to take them three times and take an average of the three.
Diagram-
This is the circuit I am going to use:
Results-
The results above are averages from three different sets of results.
Graphs-
Conclusion of graph- from the graph you can see that as the length of the wire increases the resistance increases. There is a very strong positive correlation. Why this happens is explained in my prediction. In the wire there are an amount of atoms and free moving electrons. Resistance happens when the moving electrons collide with the atoms of the wire. So when there is a longer piece of wire there are more atoms to collide with. There is a certain amount of atoms in a piece of wire and when this is doubled the number is doubled, this means that the results should be proportional.
Evaluation-I think that I carried out the method accurately so I got accurate results. I think that taking three readings and an average was a good idea and gave a more accurate result. There weren’t any anomalous results, but a few were a little inaccurate. Also the wires used to link the ammeter, voltmeter and power pack were all different lengths. But as I left the same wires in the same places in the circuit this didn’t lead to any problems in the results. All the wires used in the circuit should have been the same length and thickness. Some of the wires may have been different resistances, and this may have affected the results.
The method I used was suitable and gave me the results I expected. The results were proportional this is because if u take:
30cm=0.83W
60cm=1.6W
1.6 is roughly double 0.83 (0.83+0.83=1.66) This shows that the resistance has roughly doubled over twice the length of wire. Maybe if I had used better equipment I would have had more accurate results.
To improve the experiment I could:
- I could have used a more accurate ammeter
- A more accurate voltmeter
- Attached the crocodile clips more accurately
- Also the wire got bent throughout the experiment making it hard to measure the wire accurately
Following this would have given more accurate results.
Bibliography-
http://newton.dep.nl.gov/askasci/phy99/phy99x70.htm