This means that the surface area is inversely proportional to its resistance.
LENGTH
Double the length of the putty should double the resistance, as twice the length of the putty is equivalent to two equal resisters in the series circuit.
TEMPERATURE
The resistance for a metallic conductor is a constant if the temperature and other physical properties remained constant. In general, for metallic wires, the higher the temperature, the larger its resistance. But for some materials e.g. like silicon and germanium (used in thermistors), the higher the temperature, the lower its resistance. The resistance of most of the alloys, e.g. Constantine, is only affected slightly by a change in its temperature.
I am investigating the affects of the length and of 1/cross sectional area (1/A) as both of these factors are connected to its physical effects. It is much harder to record the temperature of the conductor than to measure the surface area or the length of the carbon putty. And the experiments to investigate these factors should hopefully give a good straightforward result. I have chosen to do two, as this way I can see if there is a mathematical formula for the relationship between the mass of the putty and the resistance it induces
From all of that information I can predict that I believe that there will be a proportional relationship between the mass and the resistive force of the putty, i.e. if the mass of the putty is increased by 10% then so will the resistance.
I have done a preliminary test using a similar method below but I have measured the current that goes across the conductor and then calculating the resistance from the data I have collected.
In the preliminary experiment, I was trying to measure the current passing the carbon putty, as it is said that R = V/I and I am therefor measuring the current by varying the length of the carbon putty. I am using a 4 Volts power pack and an ammeter to measure the potential differences passing through the conductor putty.
ACCURACY AND SENSITIVITY: I the setup I have chosen for my experiment there are four different items devised for measuring, these are the ruler, the digital voltmeter, the digital ammeter and the micrometer screw gauge, (I decided to use the digital voltmeter and ammeter’s because they were more accurate than the multimeter as the multimeter only took a reading to one ohm). Each one of these has different sensitivity and accuracy.
The digital voltmeter is accurate to 0.01 volts and is also sensitive to 0.01 volts, this means if there is a change of 0.01 volts then the reading will change also.
The ammeter sensitivity works in the same way as the voltmeter and is accurate and sensitive to 0.01 amp
The 30cm ruler is accurate to 1mm and is sensitive to around 1mm also
MEASUREMENTS: Throughout this experiment I will be measuring four things, length, cross sectional area volts and amps, In the first half of this experiment I will be adjusting the length of the putty but keeping the cross sectional area at a constant 2cm. In adjusting the length I will take 12 readings, two (amps and volts) for every different length (0cm to 10cm with a two-centimeter change every time). I will follow the same practice in the second half of my implementation except this time, the length will remain a constant 5cm and the cross sectional area will be the varied factor, with area changing from 2cm to 10cm, (only producing 10 results as opposed to 12) this is because you cant have 0cm cross sectional area so a pair of results is lost.
BACKROUND THEORY: Resistance is caused when one object is preventing others to flow, as a dam provides a resistance to water and restricts the flow of water, so does the putty restrict the flow of current only letting a little bit through over a set period of time, my aim in this experiment is to find a connection between the flow of electrical current and the mass of putty it is trying to get through.
In today’s society there are thousands of uses for resistance and more are being created all the time. The main reason for this is resistance causes heat, in turn the main use for heat caused by resistance is in fuses. Fuses blow out, when surges of electricity cause a bit of wire to melt, there for breaking the circuit, and “blowing” the fuse. The three other main uses of heat caused by electricity are, boiling water, i.e. the heating element in a kettle, an iron, although there is an independent hot plate also powered by the electricity and in some cases lighting. I.e. solar lights in an aquarium or reptile tank.
However there are also downsides to resistance as well.
IMPLEMENTATION:
I started by collecting all my apparatus and setting it up as shown
Once this was done I crafted the putty into the desired dimensions. Namely a cylinder shape 10cm in length by 2cm in cross sectional area. I did this by rolling the putty until it became cylindrical then I used a 30cm ruler and a micrometer screw gauge to check that its dimensions were uniform along the length of the putty. Once I was sure that it was a uniform diameter along the length of the putty then attached one two pence coin to each end of the cylinder. Once the coins were secure I placed the putty into the circuit with one crocodile clip attached to each coin, I then took a reading from the voltmeter and the ammeter and recorded my results. I repeated this process, shortening the putty cylinder by 2cm every time, this left me with 6 pairs of results, ranging from length (L)=0cm and going up to (L)= 10cm.
I did the experiment twice for each reading and as doing so I was looking for a pattern and accuracy. Overall I took 12 readings (2 for each of the six masses of the putty) as this ruled out any chance of miss readings and gave a better picture of the result of this.
I did the experiment again only this time I kept the length of the cylinder at a constant 5cm long whilst adjusting the cross sectional area. I started at radius (r) = 2 cm and went up to (r) = 10 cm however this time I only got 5 pairs of results as I cannot measure (r)= 0cm (this would have given me the sixth result as before).
In collecting the data, I used plastic gloves, as this carbon putty is toxic if swallowed.
Throughout the experiment I was trying to keep these factors constant:
1) The length of the putty
2) The cross sectional area of the putty
3) The temperature of the putty
4) The amount of contact between the 2p coin and the putty
RESULTS
From this experiment I have two lots of results one set for when the length was uniform and the radius was varied and another set from when the radius was uniform and the length changed was a variable.
VARIABLE LENGTH (resistance was worked out with the formula R=V/I
VARIABLE DIAMETER
I took the reading up to two decimal places’, as this allows simple yet pretty accurate results and can also show a pattern of this experiment
Analysis
Graph 1 shows that the resistance of the conductor varies with different length of the conductor. It shows a positive correlation because the resistance increases as the length increases but the relationship is not a proportional one, as the graph does not pass through the origin.
My prediction that the resistance will Increase proportionally as I doubled the length of the carbon putty was right. In the table, it is possible to see as I doubled the length I have roughly doubled the resistance. The graph and table give some example. When the length is doubled from 5 cm to 10 cm the resistance doubled from around 8 ohms to around 20 ohms.
