Hypothesis
I think that as I increase the length of the wire I will also increase its resistance. This is because if I increase the length of the wire I will be injecting more electrons into the circuit- making it harder to balance out the electrons, which means I will be slowing down the flow of electrons around a circuit. Because of this I will be decreasing the current as I increases the resistance.
The resistance of a circuit may be increased because of collisions between the electrons and the positive ions of the metal wire. The heat energy increases the collisions between the electrons, and the positive ions will increase the energy needed for the electrons to push through, therefore again, slowing down the flow of electrons around a circuit.
Because an atom consists of a nucleus and orbiting electrons it allows electricity to flow through it. These electrons can create a flow of current, so the more free electrons there are, the more conducting capability the material has. Therefore longer wires will cause an increase in resistance because the free electrons have to travel longer to get to the other end. Electrons will also collide with atoms, this is more likely to happen in longer wires than shorter ones.
The shorter wires will have less resistance because the electrons do not have to move as much as the ones in the longer wires. This means that resistance should also be proportional to the length of the wires, the longer the wire the more resistance and the shorter the wire the less resistance there is between the wire.
R ∞ Length of wire
Resistance will only be proportional to the length of the wire only if other factors remain constant like the temperature and material of the wire. For my experiment I will be using nichrome wire only, because I will be only changing one variable for the experiment. I will be using nichrome because it is an average conductor for my component under test.
Prediction
I predict that the longer the nichrome wire is the more resistance it will have. This is because the electrons have to move a further distance to get to the other end. I also predict that the resistance graph will be a straight-line graph with the gradient equal on both sides. This will happen because the current and the potential difference will be proportional to each other.
An electrical field in a conductor causes the free electrons to accelerate; as they accelerate they gain kinetic energy and pass this onto any atoms they collide with. This gives the rise in temperature.
I will have to work out the resistance using the formula V=IxR, this is because I will only get readings for the volts and amps because I will have a voltmeter and ammeter on the circuit. To find the resistance I will use R=V/I, so for example if I had 4V and 2A the resistance would be 2Ω, 4/2=2Ω. I can draw a graph of V against I and an average resistance can be produced.
The strength or size of an electric current is a measure of the rate of flow of electric charge past a point in an electric current or through a conductor. The relation between the current and charge is: Current = Charge/Time
Apparatus
Power pack, Voltmeter, Ammeter, Nichrome wire, 2 Crocodile clips, Normal circuit wires and a Variable Resistor.
Method
Through my preliminary investigation I have found out how to do my investigation.
- Gather all the apparatus and set up as shown in the diagram
- Check that the fuse is in
- Turn the voltage dial to 6V while the power pack is switched off
- Put the crocodile clips at 10cm apart and adjust the variable resistor so you get your amp reading at one amp.
- Make sure the power is on D.C rather than A.C
- Put the crocodile clips 10cm apart and turn the power on
- Record the readings from the voltmeter and ammeter and put it in your table of results
- Turn the power off
- Increase the length of the crocodile clips by 10cm
- Turn the power on
- Record the readings from the voltmeter and the ammeter and put it in your table of results
- Turn the power off
- Increase the length by 10cm each time and repeat steps 8 to 10, do this until you reach 100cm
- Repeat the experiment another two times to get an average reading so that your results are accurate.
* The ammeter must be placed in a series but can be put anywhere in the main circuit but the voltmeter must be placed in parallel with the component under test (nichrome wire).
Fair Test
To make this experiment a fair test I will only change the length of the wire, while the type of wire- nichrome wire, the same thickness, the temperature- room temperature and the voltage- 6V will be kept constant throughout the experiment.
Safety
I will have to be very careful handling the wires as they will become very hot during the experiment. As I do not touch the wire I could wait for the wires to cool down or keep the power on for a very short while. The changing of the length should only occur when the power supply is switched off.
Table of Results
Preliminary investigation at 6V & 8.84A
10cm- 1A & 043V
100cm- 0.58A & 2.49V
Preliminary investigation at 4.5V & 5.95A
10cm- 3A & 1.40V
100cm- 0.75A & 3.24V
Analysis
Looking back at the experiment, it is showing evidence that the longer the nichrome wire was the more resistance there was along the wire. The table of results shows this clearly as it goes from 10cm to 100cm increasing resistance.
The nichrome wire had more resistance when the crocodile clips were 100cm apart because the electrons being pumped around the circuit had a longer distance to reach the other end of the power supply. The atoms in the wire obstruct the path of the electrons, which slows them down, and as the atoms and electrons collide they produce heat.
Looking at my graph (1) I can see that this is true, my graph shows that the resistance is proportional to the length of wire. This is because by increasing the length of wire there will be a further distance for the electrons to travel, therefore increasing the resistance, as it takes longer for the electrons to travel back to the power supply.
Looking at the table of results I have identified trends and patterns, in my main experiment I found that the voltage increased by 0.2 to 0.4 volts until 50cm where it increased by 0.16V constantly until it reached 100cm. The amps stayed at a constant rate of an increase by 0.06A until 60cm where it slowed down and increased by only 0.03A. This showed that there was more current being pushed around from 10cm to 50cm but there was less being pushed, as the wire got longer. For the voltage it was different because the shorter the wire was the less voltage around the circuit. At 10cm there was 0.44V being pushed and at 100cm there was 2.49V, a difference of 2.05V.
My graph shows that the resistance went up steadily. Most of the dots are on the line of best fit, which shows that my graph is showing the right evidence and there is a positive correlation.
Conclusion
In my hypothesis I predicted that as the length of wire was increased the resistance would increase too. Looking at my graph (1) I can see this to be true. My graph shows that the resistance and the length of wire are proportional to each other. This is because by increasing the length of wire there will be a further distance for the electrons to travel, therefore increasing the resistance, as it takes longer for the electrons to travel back to the power supply.
In my hypothesis I predicted that as the resistance was increased the current decreased. As resistance is proportional to the length of wire I can say that my graph proves my prediction correct. This is because the resistance slows down the flow of electrons in the wire. By increasing the resistance there are more obstacles in the path of the electrons and so they don’t flow as freely.
Increasing the length of the wire means increasing the resistance. This is so because as the length of the wire is increased more electrons are inserted into the circuit making it harder to balance the positive and negative electrons, which means the slowing down the flow of electrons round a circuit. This can be used to explain why I got the result that as the resistance was increased the current decreased.
The results have shown me that the voltage does have an effect on both the resistance and the current in a circuit. Looking at my results I have found that the voltage also decreased as the length of wire increased which means that the electrons wont need that extra ‘push’ to flow through the circuit. My graph shows current against voltage; it shows as the current increased the voltage decreased, which means my graph should look like this:
Evaluation
The aim of the experiment was to find out how the voltage is affected when the current flows through wires of varying lengths. My results show me that I have done the experiment correct with minor glitches.
The quality of the evidence has been very good, I have identified one anomaly, which has shown the opposite of what I have expected, this was the V/I graph the correlations came out negatively. My resistance graph came out as I expected because all but one dot was on the line of best fit, which backs my hypothesis which states that the longer the wire the more resistance. One thing that could have affected my results was the temperature, because of temperature the resistance increases. I solved this problem by doing the longest wire first so that the wire does not heat up; I also kept the power turned off when I wasn’t recording the volt readings and amp readings. Because electrons carry heat and when they collide with positive ions of the metal wire, it transfers the heat by conduction, which increases resistance.
The procedure of the experiment was very good as it was very safe for my partners and myself. The wire was placed on a metre ruler so that you could measure the length of the wire easily. The experiment could have been improved by using digital ammeters so that you can get an accurate reading, the analogue ammeter could only read up to 1A, which meant that the ammeter couldn’t be used on an experiment checking the amp reading over 1A. Other than this I think that the experiment procedure was very good.
During the experiment I took down three readings for the voltage and amps from 10cm to 100cm. This made the evidence reliable because an average could be worked out from the readings. A problem with this was that the ammeter and the voltmeter was never still, it always changed from the first reading on the screen. The evidence was sufficient enough to support the conclusion, which proved my prediction right.
To make my work I could have added two ammeters on the circuit so that I could have got a more accurate reading, I could have also done the experiment on a longer wire I could have gone up to 300cm to see how the resistance is compared to the 100cm. This would have been a good experiment as light switches are sometimes a metre away from the light. Other then that the experiment was a good way to find out about resistance along a wire.
Bibliography
Physics a course for GCSE: Gilbert Rowell and Sidney Herbert
Modular Science for AQA: Keith Hirst, Mike Hiscook, David Sang and Martin Stirrup
NEAB Modular science: Richard Parsons