The objective of this investigation is to find the resistance of a piece of wire. I will be testing three pieces of wire for their resistance. Resistance occurs as electrons move through matter when voltage is present.

Prediction:

                   

                   I am going to choose the length of the wire as my input variable. I predict that the bigger the length of wire I measure across, the higher the resistance will be. I think that the longer the wire, the more resistance. My output variable is the resistance. I will be passing one constant voltage through different lengths of wire.                  

                                      SWG

        Copper                  26,32

        Constantan           26,32

        Nickel/chrome       26,32

I am going to use nickel as my wire choice. This will give me a varied set of results for my conclusion. This would be as electrons lose some of their energy when they collide. I will have to keep the voltage low to minimise resistance. This is due to kinetic theory, the more voltage, and the hotter the wire, the faster moving particles therefore the more energy lost through collisions. The classes are Length, thickness, temperature and material. I think the easiest to vary will be the material and the length. The hardest to vary will be the temperature and thickness. I will make sure that I produce reliable evidence by making sure I do everything precisely. This is the equation for resistance:

                            V (Voltage)

                                                    = R (Resistance)

                             I (Current)

Apparatus:

                   

                    I will be using:

Multi-Meter-

Set to 200Ω (ohms) and plug in the connecting wires.

Connecting leads-

They will transfer current from the wire through the crocodile clips to the multi-meter.

Crocodile clips-

Attach to the connecting wires and the experimental wires.

Various wires-

I will choose one of these wires to do the experiment with.

Metre rule-

I will measure out the wire along this then take readings off it.

The connecting wires and crocodile clips will give me a little resistance, so I have to account for this in my final evaluation.

Method: 

   

•     I am going to measure my nickel wire out along the metre rule. Nickel does not heat up as much as copper and constantan so it is a wise choice.

•      I will attach crocodile clips to the end at 0cm and then every 10cm. I am going to do it every 10cm until 100cm for a good range of results. I will set the multi-meter to 200Ω then take the reading and put the data into my table.
•      The thinner the wire is the less channels of electrons in the wire for current to flow, so the energy is not spread out as much, so the resistance will be higher. If the area of the wire doubles, so does the number of possible routes for the current to flow down, therefore the energy is twice as spread out, so resistance might halve.
•      I will make it a fair test by keeping one constant voltage through the wire, the same thickness, the same material and the same temperature, also to make sure I will take the reading three times.
•      The temperature will rise once current is passing through it, which will cause the atoms in the wire to vibrate, and obstruct the flow of electrons, so the resistance will increase, creating an error, but nickel does not heat up as much as copper and constantan so it is a wise choice.
•      In a book called ‘Ordinary Level Physics’, it says that “doubling the area will therefore halve the resistance-in other words the resistance of a wire is inversely proportional to its area.”
•      This is how I will set up the experiment:

 

Table:

Results for the resistance of nickel wire

          I made sure my results were accurate and reliable, by taking the reading three times. I made sure that I put the wire on the inside edge of the crocodile clips as not to get a measurement that was inaccurate. When I put the crocodile along the wire, I pulled the wire straight so it would not bend and be longer than I wanted.

Analysis:

             

                The graph of my experiment shows that there is a fairly straight line through the origin. This means that length is directly proportional to the resistance. So if the length is 40cm the resistance will be 3Ω and 80cm will be 6Ω. This is because of the scientific idea, stated in my prediction, that if you double length, you double the number of atoms in it, so doubling the number of electron 'jumps', which causes resistance. The results support my prediction, the results turned out the way I had expected.

Evaluation:

                 The data I recorded is quite reliable. Although in my graph there seems to be an anomalous result in the line, between 60cm and 70cm. Measuring the lengths of the wire is also an inaccuracy as the rulers used are not exact, and it is difficult to get an accurate reading of length by eye, as the wire might not be completely straight, the wire could also have slight thickness differences along it. These would have contributed as well to the error. This evidence is good enough to support a firm conclusion. If I did this experiment again, I would use a newer and more accurate multi-meter, a more accurate method of measurement, and take a much wider range of readings so that a more accurate average can be taken. I would also investigate other factors, such as temperature, voltage, and see how these affect the resistance. I would also do the experiments under different conditions such as temperature and pressure to see if it makes any difference to resistance.

Conclusion:

                   

                  My prediction was correct that the bigger the length the higher the resistance. But there cannot always be an exact answer and result for an experiment like this.