Prediction: I think that the length of the copper increases the current decreases. As the length increases so does the resistance. This is because the further the current has to travel the more fixed copper particles the current has to go through which increases the resistance. I can back this up with evidence from my preliminary work. I conducted an experiment using a rheostat which is like a variable resisitor that showed similar results.
My results follow what ohm said and current and resistance are directly proportional.
From these results, I have decided to leave gaps of ten CM in the wire when I do my main experiment this is to get results that are more accurate so I can draw a more accurate conclusion. In my main experiment I will sand down the paper for longer and more methodically to stop the possibility of the rubber insulating the electricity, I will also keep the temperature constant because if the wire get to hot the particles will vibrate more and cause more collisions and therefore more this would reduce current and increase resistance. I had problems with the length of wire moving during my experiment due to it not being very secure. In my real experiment, I will ensure the wire is succoured tightly to the one-meter ruler.
Equipment list
- Voltmeter
- Ammeter
- Power pack
- Copper wire
- Connecting wire
- 1 meter rule
- Crocodile clips
- Sand paper
- Masking tape
Step by step guide
- Sand down wire to remove the build up of any copper oxide of coating or to remove membrane that is there to prevent build up of copper oxide.
- Set up equipment as shown in diagram.
- Place crocodile clips on wire 100 cm apart from each other.
- Turn on power pack
- Change the voltage to 0.2v
- Repeat all of the above reducing the distance between wire the crocodile clips each time by 10 cm
- Do this three times to get accurate results and find anomalies
How to conduct a fair test
The input variable the item that I am changing is the wire length.
Output variable what I am measuring is the current.
The things I will keep the same are:
Equipment – this is because different equipment will give different results for example a power pack maybe stronger or weaker than another power pack.
Temperature – the hotter the temperature the more energised the particles will be causing more collisions and therefore more resistance.
Voltage – voltage and current are directly proportional, and as I am measuring current against length not current and voltage, so the current should not be changed.
Thickness – If the thickness of the wire was changed it would effect the equipment because the thicker the wire the lower the resistance
Safety
I will need to carry out these actions to ensure my experiment is safe:
· Keep all the equipment away from any water.
· Keep voltage at 0.2 so it is
1.) Low enough that if someone were to get a shock it would not cause serious injury.
2.) Will not burn through the masking tape and become a fire hazard.
Both these things can be easily avoided if the experiment is done sensibly and set up in an appropriate location.
Analysis
By looking at my graph I can see that as the length of the wire increases the current decreases and the resistance increases.
My current verses length graph is indirectly proportional, when you double length you half the current. Because the longer the wire the more particle collisions there is causing the current to flow slower.
My resistance verses length graph is directly proportional; when you double length, you double resistance. This is because if the length of the wire is doubled then the resistance will double as well, this is due to the increase in particle collisions with each other in the wire, which in turn is because there twice as many particles as the length of the wire has been doubled.
I can now conclude the longer the wire the larger the frequency of collisions due to more particles this then slows the flow of electrons down, causing the current (flow of electrons) to flow slower this can proven by my graphs In my current verses length graph the results are indirectly proportional, when you double the length the current halves.
From looking at my length and resistance graph I can see that they are directly proportional. So I can see that ohms law works and the proof is in these graphs.
My graphs show me that as the length increases the current decreases this is because the further the current has to go the more particles it will bump into, Thus slowing the current and causing more resistance.
I have also proven my prediction correct and I can not only say that as I increase the length of the copper wire the resistance increases I can say that they are directly proportional. The conclusion of my results shows that the prediction I made at the begging of my experiment based on Ohms law and my preliminary work was correct.
It also proves that Ohms law is correct. Ohms law states, that voltage and current are directly proportional as long as the temperature remains constant. This means that if you double the voltage you double the current. Ohm came up with a number that linked voltage and current for a certain material he called this resistance. Not all my results are exactly doubled or halved as my temperature was not exactly the same for each test only roughly.
If the temperature had not been kept constant then the higher the temperature the more energy the particles have and therefore there is more collisions subsequently giving a higher resistance and making the experiment an unfair test.
