Fair Test
To make my experiment fair, I need to make sure the voltage across the wires is the same the wires are of the same type and that the temperature remains constant and the wires don’t become too hot.
The great scientist George Ohm was the man who discovered the current through a metal wire is proportional to the p.d. (voltage) across it as long as the temperature remains constant at all times. The equation for this is
Variable change -independent variable (length)
Variables to keep the same- dependent (resistance)
There is a relationship between the voltage and the current because if you increase the voltage, you also increase the current another relationship is between the current and the resistance if you increase the resistance the current decreases.
Ohm’s law is only true if the temperature remains constant, because the atoms in the wire start to vibrate as they become warmer, which causes more movement and even more resistance.
Equipment
The equipment that I am going to use is,
- Power-pack
- Wires
- Ruler
- Copper wire
- Volt meter
- Ammeter
Prediction
I predict that the resistance of the wire increases as you lengthen the wire. I predict this because the wire contains atoms, but if you change its length the amount of atoms increase. So the wire could now be described as an “obstacle course.” So the electrons have to travel through the “obstacle course” before they can reach their destination, the end of the wire. So the more atoms give the electrons an harder task of travelling through the wire quickly without losing any voltage, so the resistance will become lower as you change the length. Also if you double the length the resistance should also double because the numbers of atoms have also been doubled.
OBTAINING EVIDENCE
Record Results
Method
I will get a power- pack, 5 wires, a voltmeter and an ammeter, and a piece of copper wire. I chose 5 wires because of my preliminary work, and also the lengths of copper wire were based on previous work. I believe that the measurements in cm, 10,20,30,40 and 50 will show a recognisable increase in resistance. I will put the wires in my power- pack and connect them to the ammeter. I will place the voltmeter in parallel to the piece of copper wire. I will put the required measurement of copper wire into my circuit to make them accurate I will measure the measurements with a cm ruler. I will then switch on the power, and take the readings of current and voltage. To make it reliable and accurate I will test each measurement three times then take an average of the readings to make the readings more accurate, I will also record my averages to at least 2 decimal place. I will have to watch the temperature of my wire constantly, so I will switch it off quickly to ensure the temperature remains constant.
Safety
To make the experiment safe I have to keep my eye on the voltage to make sure it doesn’t become to hot, because hot wires can cause fires.
Choice
I have decided to use graph two from the preliminary work I did for my investigation because the line of best fit goes through two points and there is only one below it. The measurements, are 10,20,30,40,50 cm. In graph one with measurements of 5,10,15,25,30 cm the line of best fit goes through two points but the rest are below the line of best fit.
(In bold means not included)
Results Table
The total resistance is
- 10cms; 17.5
- 20cms; 21
- 30cms; 21
- 40cms; 20
- 50cms; 21.5
ANALYSIS
Analysis
The graphs are evidence that the flow of electrons through a wire face resistance from the atoms that make up the wire, you can instantly see a rise in resistance as you increase the length of wire. If you study the graph above the relationship between the length and resistance is evident. I chose to use this data because it gives you a bigger range instead of 5, 10… of results. The results are close together which can only suggest that George Ohm who discovered resistance and his theory are in fact true, as long as you keep the variables the same. These results are also reliable and accurate as they are an average result of the table above. My prediction is that as you lengthen the wire the resistance of the wire increases because the amount of atoms increases. So the wire could now be described as an “obstacle course.”. The results of the experiment agree with my part of my prediction that as you lengthen the wire you increase the resistance, but my prediction about doubling the lengths of wire doubles the resistance wasn’t correct, as you can see the results are very close. I believe I have sufficient evidence as you can see a slight, steady rise in the resistance. The pattern would become clearer if you used longer lengths of copper wire.
EVALUATION
Evaluation
The way that I carried out my experiment was carefully and accurately. Measuring the length of the wires exactly wasn’t easy I should have used a ruler. My method didn’t include measuring accurately with a ruler I should have really included it to make my lengths easy to use. It was easy to keep the temperature constant throughout, as I just took the readings quickly in order to keep the temperature low and under my control. I kept the voltage the same so each wire received the same voltage. The 10cm and 50 cms don’t fit my pattern, but because I did the experiment to the best of my ability the only suggestions are there was something wrong with the equipment, or the wires were faulty.
Another way that I could’ve made my evidence was more reliable, by testing each measurement 5 times and work out an average resistance. I believe that I have enough evidence to reach a conclusion, because it is reliable and is similar to other people’s results. I can also test different types of wire, as I only used copper that has a low resistance, to back up and solidify my theory, because many people can argue against using one type as many different wires have different resistances, so as long as I can clearly show a rise in resistance in my results I believe that my results are conclusive.
Even though I suggested testing the wires more times or over a bigger range this would not be good enough.
I could extend my experiment by testing the wire in different conditions, ideally in water or a liquid to see if the added presence will affect the resistance. Preferably I am sure that my graph indicates if you double the length you double the resistance, this is because the atoms are arranged in a different ways in different types of wire, but if you double the same type of wire it should automatically double the resistance.
Copper is an excellent conductor of electricity and therefore has a low resistance and is often used for electrical wiring. Over a short length of wire like 50cm you won’t see big changes in resistance and therefore you can’t expect the resistance to double. I could test to see if the theory ‘double the length of wire you double the resistance’ is true by using bigger lengths of wire e.g. 100cm and 200cm.I can test my original prediction about doubling the length of wire and resistance using the wires I have chosen in this investigation by using different types of wire because some wires do double resistance even though they are small lengths and don’t require large lengths to prove that doubling the length doubles the resistance.
