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The aim of this investigation is to find out the relationship between resistance and conductive putty, and to see how length of putty affects this relationship. The Experiment: Conductive putty is specially designed to be a conductor; this is achieved by adding carbon black. This can easily be used to prove the concept of resistivity because it is malleable and so the cross-sectional area, length and shape can easily be changed. This experiment will show the effects on resistance in a circuit, as the length of putty decreases. I will be using 30cm of putty, and decreasing it by 5cm each time.
First the voltage of the battery will be taken using a voltmeter, and this will be recorded at the start of the experiment. Then a circuit will be constructed containing the battery, the ammeter and putty. See diagram. For each different length of putty, a reading will be recorded from the ammeter and when the practical has been completed, I will work out the resistance using the formula R=VI. From those results I will draw a graph and then evaluate and conclude my experiment. Diagram: Constants: My constants include the weight of my putty – I am going to start each experiment with 50g of putty.
I will also sustain the same thickness of putty throughout my experiment, and the same battery will be used constantly. Variables: Possible variables in this experiment are temperature, voltage, cross-sectional area, mass, surface area and length. My variable is going to be the length of my putty, which will decrease by 5cm each time. I am going to start each experiment, using 30cm of putty. Fair Test: To ensure my results are as accurate as possible, I will make sure my experiment is a fair test. For this, there should only be one variable.
Other procedures can ensure it is a fair test, such as accurately measuring the putty to make sure it is decreased by 5cm exactly every time. The same battery should be used throughout the experiment and to guarantee no results are anomalous, the experiment will be conducted three times and a mean average will be taken from each result. Prediction and Hypothesis: I predict that the resistance will be directly proportional to the length of the conductor so that if the length is doubled, the resistance will double providing all other factors remain constant.
My hypothesis for this is that conductors have lower resistance when they are shorter because the electrons have a shorter distance to travel so more energy is conserved since there are fewer collisions, and the current is higher. In the longer lengths, as free electrons move from atom to atom some energy given off to heat. The longer a conductor is, the more energy is lost to heat. The additional energy loss subtracts from the energy being transferred through the conductor, resulting in a decrease in current flow and an increase in resistance Safety:
The conductive putty is a harmless, non toxic and non-staining, however if gloves are not worn, your hands become black and you will need to wash them. A lab coat should be worn to minimize marks on clothes and the experiment is conducted on a tray to reduce the possibility of a messy workspace. Apparatus list: – 50g of conductive putty – 2 coins – Tray to work on – Knife – Ammeter – Ruler – Voltmeter – Wires – Crocodile clips – Gloves Method: – Put on gloves and rolled putty into 30cm long piece on the tray, trying to keep the thickness consist ant. – Used voltmeter recorded the voltage of the battery.
– Connected battery to ammeter, and connected ammeter and other terminal of battery to putty by putting crocodile clips on the ends of the wires, clipping them to coins and placing coins at either end of the putty, this was done to make a reliable connection. See circuit diagram. – Recorded reading from ammeter. – Measured 5cm of putty with ruler and cut with knife. – Re-attached putty to circuit. – Repeated process, deducting 5cm from putty’s length each time, recording the reading from the ammeter. – Repeated experiment three times, which will enable me to spot anomalous results.
Results: I have calculated the resistance using the formula: R=V/I. Resistance is measured in ohms and the unit uses the symbol ?. Experiment 1 – battery voltage = 6. 12V: Length of putty in cm Amps in A Resistance in ? Analysis of Results:
This graph shows me the results for all three of my experiments, and there is a line of best fit for each experiment. There are some inaccuracies as the voltage was slightly different for each experiment, and I feel that points for the later experiments are also out. This is visible in my results and is maybe due to the fact that the same piece of putty was used for all three experiments, and so heat from my hands must have affected results. I have taken the averages of my results.
Length of putty in cm Resistance in ? These are my average results. These results were plotted on a graph (see graph) and they show a visible decrease in resistance as the length of putty decreases. This would prove my prediction and hypothesis to be correct, as it states that the putty will have lower resistance when the length is shorter rather than longer or the resistance of a conductor is directly proportional to its length; due to factors such as loss of energy to heat, higher rate of collisions etc.(see prediction and hypothesis)
However, when looking at my graph I noticed that the two points representing the shortest lengths of putty were out. This could be because as the putty was being worked, rolled and cut throughout the experiment it had become warmer and softer due to the heat from our hands; this could have affected the resistance. Evaluation: My results have proven my prediction and hypothesis to be correct, in that resistance is directly proportional to the length of the conductor, in this case the conductive putty.
I think my results were quite accurate, but what may have let them down was the fact that the battery’s voltage was slightly different for each experiment and the coins used to connect the wire to the putty, did not stay in place very well. I also noticed there was often a big jump in amps and resistance between 10cm and 5cm of putty. This can be seen by looking at my results and the graph, and I have concluded that this is probably caused by my hands transferring heat to the putty by means of conduction, as the putty is regularly in contact with my hands during the experiments.
I expect this could be separate experiment, in which we could investigate how temperature affects resistance. If this experiment was going to be redone, then I think I might use a new battery for each experiment, and record the voltage as constant for all experiments. Also I would maybe use a different method to connect the wires to the putty, like maybe sticking the wires directly and vertically into the ends of the putty.
Another thing to do would be to use temperature or even cross-sectional area as a variable alongside length, and to do a series of experiments involving increasing the length while decreasing the cross-sectional area, and vice versa. Conclusion: I think this experiment was a success in that it proved the theory that resistance is lower with shorter lengths of conductor and my hypothesis declares that as the electrons have a shorter distance to travel if the length is shorter, there are fewer collisions and less energy is lost to heat unlike in a longer length of conductor, so the putty will have lower resistance.
Therefore my hypothesis was correct and I have successfully concluded my experiment proving that resistance is directly proportional to the length of conductor. Show preview only The above preview is unformatted text This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.