Background Information Aim of Experiment The aim of this experiment is to find out how the length of constantan wire changes the resistance of it when it is connected to an electric circuit and electric current flows through it. Hypothesis I predict that as the length is increasing the resistance will increase directly proportionately. I believe this because during the experiment the resistivity and area will stay constant and the formula for this experiment is R(A) x l, we can see that the resistance is directly proportional to the length because as the length increases by the same amount like for example 10cm then the resistance should also increase by the same amount every 10cm. I also believe that the current flowing through the entire circuit will be less due to the resistance. I also predict that the resistivity of the constantan wire will be constant at 4.9 x 10-7m or very close to it because that is the regular value for the resistance of constantan wire. Explain the science behind this. In Physics use a formula for your scientific reasoning if possible Variables Independent variable The length of the wire. The different lengths of the wire are 50cm, 60cm, 70cm, 80cm, 90cm. Dependent variable The current and the voltage which then using the formula R VI (Where Rresistance, Vvoltage Icurrent), will help me to find the resistance of the various lengths of wire) Control variables Temperature of wire Diameter of wire Type of wire Room temperature Changes in temperature can change the resistivity of a material All the other materials that are parts of the circuit that are also listed below should stay the same during the entire experiment, including the Ammeter, Voltmeter, electric cables, battery or power source. Generally the entire set up of the circuit All these things should be kept the same to create a fair and balanced testexperiment and allow for accurate data that is produced and can be collected so that correct conclusions can be made after the experiment. Materials Ammeter Voltmeter Electric cables (with crocodile clip ends and normal ends) Ruler (100cm) Constantan Wire (should be over 100cm so you can put it on the ruler and have a diameter of 0.274mm) BatteryPower source Method List of numbered steps 1,2,3 … so that another scientist could follow your method. Gather all the materials listed above. Make sure that they are all in the correct shape and condition. For example Make sure that the battery is charged enough with and contains at least 1.5 volts so that you can get good results. 2. Before collecting any data you of course need a table for data collection that looks like the one you can find in the Data Collection section. You should have 5 data points, one for each length you chose as your independent variable above. Perform 3 trials for each length. 3. Now set up the circuit using the materials so that it looks like shown in the diagram below. When you connect the circuit, dont connect the voltmeter and ammeter just yet. Only first connect all the other parts of the circuit to each other. 4. Once you have all other parts of the circuit connected, turn the voltmeter to 20V and the ammeter to 10A and only then connect them to the circuit. Make sure your entire circuit looks like the diagram below. 5. Now start making your measurements. Take the end of the cable that is connected to the battery in which the end of a cable connected to the volt- or ammeter should be in and hold that onto the wire at the position on the ruler which shows the length you would like to measure. While holding that end of the cable onto the wire look at what the ammeter and voltmeter show and record that data into the table you created. 6. Now perform step 5 for all lengths you chose to measure the voltage and current for, and indirectly the resistance for and collect the voltage and current results and record them in your data table. 7. During the experiment be sure to keep all the controlled variables constant that are listed above. Explain exactly what you will measure and how you will measure it how you will manipulate your independent variable how you will keep your control variables constant the number of data points and the number of trials you will have how you will find a specific quantity like the gravitational field strength g (usually from the gradient of your graph) How you will make your method safe. If you do not perceive any hazards, then state this explicitly. Safety Watch out for pieces of wire of shorter length heating up as they heat up relatively quickly when they are connected to a circuit and a current flows through them over a long period of time. Diagram a clearly labeled diagram. Alternatively you can take a suitable () picture and label it. Single battery Ammeter A Constantan wire V Voltmeter The following is assessed through criterion C. Data Collection Data processing To find the resistance of wire of a certain length we use Ohms law which is V IR. To put this formula into terms of R we have to rearrange it, which would make it R VI. An example calculation for this would be To find the resistance of a piece of wire 50cm long, we take the voltage and current for that length and put it in the formula. So R 1.300285 which means that R 4.561403509 (This value is rounded up. The table below shows this number even more accurately). Graph Resistivity of wire in ohms () Length of wire in meters (m) Interpretation and description of your results Put this in step by step The data shows a directly proportionate relationship and a positive gradient. The data from the graph can be used to calculate the resistance of the wire. The calculations to find the resistance are the following We know that the formula for resistance is R(A) x l, where R is the resistance, (rho) the resistivity, A the cross-sectional area of the wire and l is the length, And the formula for this kind of graph is ymxb. For this particular graph this formula then is y8.939×0.2143. Therefore m, which is the gradient, equals 8.939. We can now use this to find the resistivity of the wire. So, because mA, m x A. At this point we only know what m is, so we need to find A to find the resistivity. To find A we do the following The formula for A is x radius2. We know the diameter of the wire is 0.274mm which means that to find the radius we do 0.274mm20.137mm. But before we put this number in the formula we have to convert it to an SI unit which means that we need to convert it to meters. We need to times 0.137mm by 10-3 to have it in meters. This equals to 0.000137m . Now we can put this in the formula and find A. So A x 0.0001372, which means that A 5.896455252 x 10-8. Now we put this in the formula to find resistivity 8.939 x 5.896455252 x 10-8, so 5.27081435 x 10-7m. Rounded up that is 5.3 x 10-7m. But the normal value of resistivity of constantan wire is 4.9 x 10-7m, which means that there is a deviation. To give us a more accurate idea of how big this deviation is we need to calculate the percentage deviation. To find the percentage deviation from the standard value for the resistivity of constantan wire and the value I got we do the following calculation ((observed – expected)expected) x 100. So ((5.3 x 10-7) – (4.9 x 10-7)(4.9×10-7) x 100 8.163265306. This means that the percentage deviation is 8.2%. What exactly does your data show Be elaborate and accurate in your conclusion. Does your data show a linear, proportional or inversely proportional relationship Is there a positive or negative gradient Give the scientific reasons for the results obtained. Use a formula if possible. Calculate the specific quantity you are looking for, e.g. the gravitational field strength. Validity of the hypothesis My hypothesis was valid as several things I predicted in my hypothesis turned out to be true. The first thing I predicted was that as the length increases the resistance increases directly proportionally because the resistivity and cross-sectional area stay the same. I found the length and the resistance to increase directly proportionately. Another thing that I predicted correctly and that further proves the validity of my hypothesis was that the current would decrease as the length of the piece of wire increased. On the other side something that makes my hypothesis less valid is that I predicted the resistivity of the wire to stay constant at 4.9 x 10-7m which didnt happen as I calculated the resistance to be 5.3 x 10-7m which means it was higher by 8% and means that not only was the resistivity of the wire was measured but also the resistivity of other parts of the circuit or the entire circuit. Overall my hypothesis is more valid than non-valid as I predicted more things correctly than wrongly. Discuss whether your hypothesis is valid, i.e. list why it is and isnt valid., then conclude. Validity of the method In general, the method of the experiment was not very accurate. This because there were several problems with the circuit. The temperature in the room while testing might have been different from when the normal value of resistivity of constantan wire was measured which could have lead to the deviation in resistivity. One problem was that the end of the wires and the crocodile clips werent in the best condition anymore which means that the electricity might not have been able to flow as freely as could have which is probably a reason for the deviation in the resistivity of the wire. Another reason for the deviation is that the not just the resistance of the wire was measured but also the resistance of other parts of the circuit such as the volt- and ammeter or generally the entire circuit. how suitable was your setup for collecting the data you needed Discuss Where applicable compare the specific quantity you were looking for to the literature value. Improvements or extensions The biggest improvement for the setup is make sure that all parts of the circuit are in good condition, like that the ends of the cables and the crocodile clips arent rusty and to find a way so that just the resistance of the wire is measured in this experiment and not the resistance of other parts of the circuit as well. All these improvements would make the data collection a lot better meaning that more accurate conclusions could have been made. I could have also extended this experiment by taking more lengths. Either down, lower than 50 cm or up, more than 90cm, to give me more data points which will most likely give me more accurate data after processing it. What could you have done differently to improve the setup Explain in detail how realistic changes in your setup would have made the data collection better. Alternatively mention ways that would make the investigation better (extension), e.g. use a greater range for the independent variable.