Resistivity of Wire

• Type of metal in the wire

-The type of metal is likely to affect it because of the number of free         electrons in the wire, these change for each metal.

For the preliminary work we chose a suitable type and thickness of wire, so only one factor remains. We are going to investigate how the length of the wire affects resistance.

We have done preliminary work in which we did an experiment to find the best type of wire and the best thickness. These are our results:

Types of wire

Thickness

This has influenced the plan of our experiment because we now know that the type of wire we are going to use is Nichrome because it didn’t get very hot and it doesn’t have a particularly high or low resistance. We are going to use 26 SWG’s because it didn’t get too hot.

Our prediction is that the shorter the wire the lower the resistance (high amps, low volts.) So that means the longer the wire the higher the resistance (low amps, high volts.)  

Method:

We are going to make a circuit which includes:

• Power pack
• A volt meter
• An ammeter
• A meter rule which is attached to a piece of Nichrome wire.

We are going to read volts and amps off the meters to see what length of wire produces what readings, for these two measurements. We are going to take 10 different readings at 100cm, 90cm, 80cm, 70cm, 60cm, 50cm, 40cm, 30cm, 20cm and 10cm. If we went any lower than 10 the wire would glow and be very hot just like a light bulb. We are going to change the length by placing the wire across a meter rule (to also keep the wire straight) and move the crocodile clip along for each measurement. For example when we measure 100cm the crocodile clips will be 1 at each end, but for 40 there will be one at 40cm and one at 0cm.

These are our results for this experiment.

From my graph I can see that as you increase the length, then the resistance also increases. The line on the graph is straight and it is a clear slope. Our results show us that the longer the piece of wire the bigger the resistance, this might be because there is more wire, more electrons moving around the wire, this means more energy has to be used to push them along (greater resistance.) When the wire is short the electrons have fewer particles to go through (not many things opposing the electrons) but when the wire is longer the electrons have more particles to get through, more things are opposing the electrons. This shows that the longer the wire the bigger the resistance.

Our results match our prediction, we were correct.

I think that the experiment was good at answering the aim as we have found out how the resistance of a piece of wire can be changed. I can notice two slightly anomalous results (circled) in my graph. These were at 20cm and 60cm; there readings fall slightly off the line of best fit. I can say that I found out how the resistance of a piece of wire can be changed by saying that for the Nichrome wire, if you change either the length of wire, the volts or the amps then the resistance will change.