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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.