So therefore the smaller the length of the wire, the less voltage there is and a bigger current can be induced with lower resistance. The longer that the wire is, the further the electrons have to travel.
If the arrangement of the atoms is irregular the atoms find it harder to move therefore increasing resistance.
The longer that the wire is, the further the electrons have to travel.
The amount of routes that the atoms can take varies on the width of the wire. More routes are possible when the width of the wire is larger. Here are a few simple diagrams to illustrate how the width affects the resistance:
1 width = 1 route for the atoms = 1 resistance
2 widths = 2 routes for the atoms = ½ resistance (0.5)
3 widths = 3 routes for the atoms = 1/3 resistance (0.33)
4 widths = 4 routes for the atoms = ¼ resistance (0.25)
When the wire is twice as thick as previously, then there are twice as many routes for the electrons to take so the resistance will be half the previous amount. From this we can predict a graph that we would expect to see.
This graph shows that the bigger the width, the lower the resistance.
The type of material will affect the amount of free electrons which are able to flow through the wire. The number of electrons depends on the amount of electrons in the outer energy shell of the atoms, so if there are more or larger atoms then there must be more electrons available. If the material has a high number of atoms then there will be a high number of electrons causing a lower resistance because of the increase in the number of electrons. Also if the atoms in the material are closely packed then the electrons will have more frequent collisions and the resistance will increase.
When the temperature of a metal increases the resistance of that metal increases. This is because when the temperature increases the atoms of the metal vibrate more vigorously because of the increase in energy. This means that the electrons have more difficulty getting through the wire as they collide with the atoms which are in their pathway. This increases the amount of collisions, therefore there is more resistance. However it is hard to keep the temperature exactly the same as the room temperature might change from day to day. A low voltage will have to be used because a low current that will not heat up the wire. If a high voltage is used the energy would be in form of heat which would make the experiment unfair.
All the information that I have used has been from my exercise book and from the ‘Physics 4 U’ text book.
The variable that I am going to be investigating is the length of the wire. I am investigating this variable because I think that this variable will be the fairest to investigate. The temperature would be very difficult to keep constant. It is hard to obtain a variety of materials, so therefore I will not be using this variable and it will be difficult to make sure that all of the different materials are of the same width. The width would be difficult to use as a variable because of having to obtain a large enough variety to allow us to make many readings, and to make our graph accurate. So therefore I have come to the conclusion that by changing the length of the wire, I will be able to obtain enough results to produce an accurate graph.
I predict that the longer the wire is, the more resistance there will be.
I think this because looking at the diagrams I did earlier, I can see that the longer the wire is, the more atoms that the electrons will have to negotiate. The electrons will have to use more energy to get past the atoms because each of the atoms would be trying to keep the electrons instead of letting them flow freely past.
Preliminary testing
This is my table of results that I got when I did my preliminary testing. I was testing to see whether I was doing my experiment fairly and to see whether I would encounter any problems. When I was setting the experiment up, I found that the voltmeter was faulty and that a few of the crocodile clips were also faulty. After finally setting up the experiment with everything working correctly I was able to collect the above results.
The experiment worked well and we found that a stronger ammeter is needed to measure below 40cm because otherwise the needle went off of the scale.
Method
Equipment:
- A metre ruler
- Crocodile Clips
- Power Pack
- An ammeter
- A voltmeter
- A length of wire (roughly 150cm)
A length of wire is taped at both ends to a metre rule. It is then attached to a circuit consisting of an ammeter in series and a voltmeter in parallel. One crocodile clip will be permanently placed at one end of the wire and another crocodile clip will be moved along the wire to produce different lengths for us to take readings from. I will take readings from the voltmeter and from the ammeter and put these into a table. This will give a range of readings to determine resistance using the formula R=V/I. Then I will plot the results on a graph, so that I can analyse my results and find out whether Ohm’s law works.
This diagram shows how the equipment will be set out.
Table of results:
From my graph I have found out that the resistance increases as the length increases. From my graph I have found that Ohm’s law works and that the resistance is proportional to the length of the wire.
Examples of this are:
30cm: 1.4 Ω
60cm: 2.79Ω
40cm: 1.88Ω
80cm: 3.83Ω
On my graph I have drawn a line of best fit so that I would be able to accurately predict the resistance of a length of wire that I have not yet measured.
