If the small resistor represents a short wire and the 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.
Prediction:
I predict that if the length increases then the resistance will also increase in proportion to the length. I think this because as I know from my background knowledge that:
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 jump 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. My graph should show that the length is directly proportional to the resistance.
Predicted graph:
Safety Precautions:
There are not many safety precautions that need to be taken into consideration, in this experiment. The main two I can think of are stated below:
Do not carry out the experiment in wet areas, as water is a very good conductor, and thus could be very dangerous.
Do not touch the wire when the power pack is switched on, because the current would heat up the wire.
Diagram of Apparatus:
Voltmeter Power pack
Nichrome wire
Meter Ruler Crocodile Clips
Connection Leads
I set up my experiment as shown above.
I started the experiment by attaching the Nichrome Wire (over 80cm long) to the meter ruler then cut to size. Then the power pack was switched on which was connected to the Nichrome wire via the crocodile clips. The resistance was then recorded down for various lengths ranging from 20cm to 80cm. I recorded each in a table.
To collect the data for my graph I had chosen to take a range of 7 lengths. I had chosen a range of 7 as to plot an accurate graph I will need at least 7 points to mark on the graph. The lengths that I had chosen were as follows: 20cm, 30cm, 40 cm, 50cm, 60cm, 70cm, and 80cm. I have chosen these lengths because they are easily measured by the meter ruler and give a good range of results. I will repeat my results three times using different currents for each.
Results Table:
Conclusion:
The graph is a straight line through the origin, which means R, is directly proportional to L. This means that if the length is 40cm, and resistance is 4ohms, then if length is doubled to 80cm, resistance also doubles to 8ohms.
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, they match the predicted line well. I had predicted a straight line through the origin, which means R, is directly proportional to L.
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 very reliable. I know this because my graph does not show any individual anomalous results. I can see on the graph that none of the results plotted are anomalous because all the points lie along the same straight line.
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. This would have contributed as a slight error in my results. As this factor probably only made a slight difference, it did not affect 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. To solve this problem, I would have found 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
I also found that the experiment was quite easy to set up, as it was simple and uncomplicated.
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)
Wire width:
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.
Stuart Mc Gaffin
