Prediction
I think that the smaller the wire the smaller the resistance because i know 4 factors that affect resistance: temp, thickness, length and material of wire these effect the resistance because
Temp: as the temperature increases the atoms in the wire vibrate more, each one moving around a fixed point so it can only move a certain distance from this. There is more chance of the electrons colliding with the vibrating atoms, so less current can flow. An increase in temperature increases the resistance of a wire.
Thickness: If a wire is thicker, the moving electrons in a current are spread out over a greater area. There is less chance of an electron colliding with an atom, so more current can flow so, increasing the thickness of a wire decreases its resistance.
If a wire is longer, the moving electrons have further to go, so there is more chance of an electron colliding with an atom. Increasing the length of a wire increases its resistance.
If a wire is longer, the moving electrons have further to go, so there is more chance of an electron colliding with an atom. Increasing the length of a wire increases its resistance.
Due to all these factors this is why I have thought that the smaller the wire the smaller the resistance
Testable hypothesis
along with my prediction I will also have a testable hypothesis to see if I can make a prediction that I can test it, for my hypothesis I think that if I double the length of wire the resistance will also double I think this because of ohms law, ohm’s law states that the voltage across a component is directly proportional to the current through it provided its temperature does not change. This les to an equation know as ohm’s law equation : so if V is set fixed at 3 Volts then if the current increases due to the length shorting then it follows that resistance must be less, also if the current doubles as the result of halving the length then the resistance must be half its original value.
Further Science to explain this
Electrons have to flow through the wire. As they flow they find wire particles vibrating and opposing their movement along the wire. (this is resistance). If the wire it long there are ,ore opposing their movement so only a few will get through every second so the current is small and resistance is high, if the wire’s length is halved there will be half the number of particles opposing them so the resistance will be half but the current will have doubled. I predict from this that the length of wire is proportional to the resistance to the wire
Apparitions
Power pack - use to make the current flow around the circuit
Wires
Length of constantan wire (30SWG)
Meter rule – used to measure the length of the wire
Range: 0.00cm – 100.00cm
Accuracy: 1mm
Micrometer – to measure the cross section area of the wire (this should stay constant)
Range: 0.00mm – 25.00mm
Accuracy: 0.01mm
Ammeter – to measure the current within the circuit
- Range: 0.0A – 1.00A
Accuracy: 0.02A
- Range: 0.0A – 5.0A
Accuracy: 0.2A
Volt Meter - to measure the p.d across the wire
Range: 0.0v – 6.0v
Accuracy: 0.2v
Diagram
Method
First a length of wire over a meter long is sellotaped to a meter rule. The positive crocodile clip is attached at 0cm. And the negative is moved up and down the wire, stopping at 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100cm. Each time reading the ammeter and voltmeter to work out resistance R = V/I. This is using 30 SWG wire. Once this is done for each length repeat 2 more times other variables, voltage, thickness, and temperature will be kept constant, although the temperature will rise once current is passing through it.
A Report of the Investigation
Micrometer Results
Results
* 0.00 was just the complete circuit with no 30 SWG Wire attached
Graph of results
The graph of results is attached on the next page
Conclusion
The results show that as the wire gets shorter the resistance gets lower and the average current gets higher, this is because the when the wire is short there is less wire to get through less wire than the longer lengths and also less constantan particles opposing the flow of electrons, as a result more can get through every second so the current reading is bigger. The graph is a straight line thought origin. In science this means the two variables are directly proportional to each other. In this case length of wire is directly proportional to the resistance. Doubling the length will double the size of the wires resistance. This makes sense as a piece of wire twice as long providing the cross sectional area is constant, which it was in this experiment, will have twice as many particles opposing the flow of electrons so the resistance will be twice as big. From this it is also possible to deduct that the current will be twice as big. Looking at the results within the experiment, within experimental area this is true
E.g. When the wire was double in length from 30.00cm to 60.00cm the average current fell from 1.43A to 0.73A (approximately half) and the resistance increases from 2.09Ω to 4,13Ω (again approximately, doubles)
Evaluation
In this experiment we made it as reliable as possible because every time we retested the results and we did this 3 times we used a different piece of wire the same SWG and length we changed this because as the current gets bigger the wires temperature increases which make the particles vibrate more which means that this opposes the flow of the electrons.
To try and make the accurate and reliable we read the results straight on so that they where as accurate as possible, by repeating the experiment 3 times to get 3 sets of results and from that I worked out a average which is more reliable and accurate than one set of results. Also 8 different lengths were tested and small currents could be read to an accuracy of 0.02A
My graph shows some anomalies which are ringed on the graph, these could have been caused by the wire heating up opposing the flow of electrons also the wire could have had a kink in it which would also oppose the flow of the electrons as there is then a narrowing in the wire so less electrons can get through per second. I could also have used a length not exactly 200mm, 300mm etc. it is difficult to get this length accurate as some of the are is gripped in crocodile clips
To make this experiment more reliable we could use a different piece of wire for each length then if the temperature increases which opposes the flow of the electrons it would not effect the next reading at a different length. To make the results more accurate I could use a digital ammeter and digital volt meter which are accurate to 0.01A and 0.01V, if I was using theses also they cannot be misread like the normal ammeter and voltmeter as it is a digital display.
To extent this investigation we could take more readings for example every 5cm in stead of 10cm and increase the maximum wire length to 200cm, also do more repeats, 5 times and not 3. Other experiments that could be done is to change the voltage and see how this affects the current and resistance. Also we could include temperature readings to see how the temperature is affected by the current voltage, and resistance. This would involve using temperature sensor touching the wire; the temperature sensor could be plugged into a data logger that will collect the readings
The original method is reliable and gave me some useful results. It is reliable because I have tried it 3 times before to find out about the current through a resistor, a bulb and a diode and each time my results agreed with the notes in the revision guide (Lonsdale Science Revision Guides, The Essentials of AQA Science: The Tested Modules, The Terminal Examination and The Additional Modules
