The reason I am not using variable resistor is because if you put the crocodile clips on 19cm instead of 20cm, you will get 5 wrong readings (all for 19cm).
Prediction:
I predict that the longer the length of wire, the higher the resistance is. I think this because there are more metallic atoms in the wire, these will obstruct he electrons trying to get through more.
As the electrons in an electric current move around a circuit, they bump into the atoms in the wires through which they pass. Atoms of different elements block the electrons to different extents. For example, electrons pass easily through copper wire, but much less easily through Constantan wires. We say that copper is lower resistively than Constantan. This is why copper is used for the connecting wires and cables in electrical circuits.
When an electric current passes through thin Constantan wire, the electrons cannot flow easily. They collide with the metallic atoms in the wire. This causes the atoms to vibrate more quickly. This causes the wire to warm up and release heat energy. If the resistance of the wire is low and the current is large, the wire may get red hot. Conductors like this that provide a high resistance are called resistors.
This statement can help to predict the fact that as the length of wire increases the resistance increases. If you double the length of wire, the amount of atoms double which means it will take double the time for the electrons to flow through the wire. The diagram below helps explain this.
The electrons in the longer wire will obviously take longer to get past the atoms than in the shorter wire.
Set up:
We set up the experiment just as shown below.
XC
Constantan wire
Preliminary results.
Before doing the proper results, we did a preliminary test to see how much we should change the wire after each result. We decided on 5cm because we found that there was a substantial change but not too much so this meant that we could get a good graph and a good set of results.
The test showed that the results are consistent and that the gap is enough to see a substantial difference.
Skill area O: Obtaining evidenceThis is the method that will be carried out to connect the circuit and achieve the specified results:
- Connect the apparatus to form the circuit, as shown on page 2.
- The wire (Constantan) should be sellotaped to a meter rule to keep it straight; this allows the flow of electrons to pass easily and without blockage.
- Connect the crocodile clips at either end of the 50cm length of wire.
- Take the reading of the ohmmeter.
It is important to take the 3 repeated readings to eliminate any anomalous values and so that a final defined and reliable average can be produced.
We reduce the wire length by 5cm to prove that as the length decreases the resistance decreases, or vice versa. Now with 45cm we used the same method to record resistance of the wire. The whole procedure should be followed through each time, while changing the length of wire by 5cm.
When all of the results have been collected we must work out the average set of results for the graph.
We didn’t need to take any safety precautions, as there was no harm of getting hurt. We just had to be careful when connecting wires together to avoid getting an electric shock.
Skill Area A: Analysing evidence and drawing conclusions
My graph shows that as the length increases the resistance increases. The line on the graph is a straight line, which shows they are proportional, or they correlate. This means that if you double one, you double the other.
My results prove my prediction was correct. My results show that as the length increases the resistance increases, (my diagram on page2 helps explain why). This is what I expected therefore my prediction was correct. I said that the longer the wire, the more atoms there are for the electrons to bump into therefore the larger the resistance. These results are exactly what I expected them to be. My graph on the next page helps to show this.
When the wire wasn’t connected, I found that there was still a slight reading on the Ohmmeter it always read 0.2. This is because the crocodile clips had a slight resistance.
Skill Area E: Evaluating evidence
I believe the method used was a very good way of investigating this topic. It was done with precision, accuracy and the results produced were reliable. The investigation was not rushed to make any of the results outstandingly uneven.
As I was very careful, there were no anomalous results. This was good because it gives more precise
The results are good enough to draw a firm conclusion, as an accurate graph was produced from them.
To extend this investigation I could observe the effect of resistance on different types of wires, such as their shapes and materials, and also to observe any other behavior such as energy loss through heat.
If given further time I would investigate whether the pattern in my results is true beyond the range of values already used in this investigation. To test the theory I would perform the test on an increased range of lengths to see what further affect it would have on the resistance. Other aspects that could be investigated are the various variables mentioned in the planning.
