The things I could measure are:
Current using an ammeter. This would tell me the amount of current flowing through the circuit.
Resistance using a multimeter this would tell me in ohms the amount of resistance the wire had.
My question will be how will the length of a piece wire affect the amount current flowing through it.
Prediction:
I think that when the length of the wire is increased the lower the amount of current that passes through so thus the higher the resis6tance the wire has now.
Electric current is the movement of electrons through a conductor. In this experiment a metal wire (Nichrome will be the conductor). So when resistance is high, conductivity is low. Metals such as Nichrome conduct electricity well because the atoms in them do not hold on to their electrons very well. Free electrons are created, which carry a negative charge, to move along the lines of atoms in a wire, which are in a lattice structure. Resistance is when these electrons, which flow towards the positive, collide with other atoms; they transfer some of their kinetic energy. This transfer on collision is what causes resistance. So, if we double the length of a wire, the number of atoms in the wire doubles. This increases the number of collisions and energy transferred twice, so twice the amount of energy is required. This means the resistance is doubled. The total resistance of resistors in series is the sum of the resistance of each one. Each cm of wire has a particular resistance, if you double the length of wire; it is like having two of the shorter wires in series. If a small resistor represents a short wire and a large resistor is a long wire of double the length of a short one. One short wire has a resistance of 1ohm, 2 short wires have a resistance of 2ohms when connected in series. The long wire is just like two short wires put together.
Method:
Apparatus: piece of 30cm Nichrome, 30cm ruler, connecting leads, crocodile clips, power pack
I started the experiment by sellotaping the Nichrome Wire to the 30cm ruler. Then the ammeter was switched on which was connected to the Nichrome wire via the crocodile clips as was the power pack and voltmeter. The voltmeter was placed in parallel to the wire. The amount of current flowing through the circuit was then recorded for various lengths ranging from 2 to 30cm. I then plotted these results on a graph.
To collect the data for my graph I had chosen to take a range of 15 lengths. I had chosen a range of 15 as to plot an accurate graph I will need at least 15 points to mark on the graph. The lengths that I had chosen were from 2cm through to 30cm in 2cm increments. I have chosen these lengths because they are easily measured by the 30cm ruler and give a good range of results. .
I will repeat my results three times.
Fair test: Below are the factors I will try to keep constant during this experiment and how I will do this. I have explained earlier in this investigation why I need to keep these factors constant.
- No. Of volts: I am using 0.5 volts and will make sure this stays constant by placing a voltmeter into the circuit so I can continually check that the voltage is constant
- Conductivity material: I will use the same piece of wire for each experiment so thus the wire will have the same conducting properties each time
- Cross sectional Area: As is aid I will use the same wire each time so the standard wire gauge is the same and also I will try to keep the wire straight so no bends occur as this could cause the width of the wire to change. This could then lead to that part of the wire allowing more or less current through.
- Temperature: All the readings will be taken within a short space of time and also I am only using 0.5 volts so the voltage should not cause the temperature of the wire to change significantly.
My graph and results show that when the length of the wire increases the less amount of current that is let through the circuit. Another pattern I found though is that looking at the current that was let through at 2cm, then 4cm and then 8cm. From looking at these three I could see that the current let through 4cm of wire was near enough half let through at 2cm and at 8cm it was near enough a quarter of 2cm. So thus I can say that the resistance is directly proportional to the length. Double the length and double the resistance
Why I found this pattern
This is because of the scientific idea, stated in the planning 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 predictions well, the results turned out the way I had expected. So, this effectively means that if the wire was trebled or quadrupled then the resistance would also treble or quadruple.
Evaluation:
From my graph I can see that my results that I collected are fairly reliable. I know this because my graph does not show any individual anomalous results and also the highest percentage error I encountered was only 2.4%. I can see on the graph that none of the results plotted are anomalous because all the points lie along the same curved line.
However I can see that my results are not completely accurate as well. I can see this because the 4cm measurement was not exactly half of the 2cm measurement as the theoretical science dictates it should be. Below is why my results were slightly out.
When I was measuring the lengths of the Nichrome wire, my measurements might have been slightly inaccurate as the rulers used might not have been exact, and it was difficult to get an accurate reading of length by eye, as the wire was not completely straight, so it may have been of different thicknesses throughout the length. This would have contributed as a slight error in my results.
The crocodile clips and the connecting leads could have affected the fairness of the experiment. They are a different type of metal from the Nichrome wire and may have different properties and therefore different resistance. Therefore the current shown on the ammeter was slightly more than it actually was. To solve this problem I would have to next time find out the resistance of the connecting leads and crocodile clips before each experiment and minus it from the overall resistance of the Nichrome wire plus the connecting leads plus the crocodile clips.
C = a - b
A = overall resistance of Nichrome wire, crocodile clips and connecting leads
b = overall resistance of crocodile clips and connecting leads
c = resistance of Nichrome wire
To make my experiment possibly more accurate I could have got 4 0r 5 sets of results and found an average but this would be too time consuming.
Further experiments I could do related to the resistance in a wire, would be to see whether the following factors would make a difference in the resistance of a wire: (I have made a prediction for each factor from my own scientific knowledge on how I think the resistance would change in a wire for that particular factor)
The Wires Cross sectional area:
I think that if the wire width is increased the resistance will decrease. This is because of the increase in the space for the electrons to travel through. Due to this increased space between the atoms there should be less collisions.
Temperature:
I think that if the wire is heated up the atoms in the wire will start to vibrate because of their increase in energy. This causes more collisions between the electrons and the atoms as the atoms are moving into the path of the electrons. This increase in collisions means that there will be an increase in resistance.
Material:
I think that the type of material of the wire will affect the amount of free electrons, which are able to flow through that wire. This is because 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 there will be high numbers 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.
