Lab report物理实验报告英文.docx

1、Lab report物理实验报告英文IntroductionCapacitor is widely used in a variety of fields as it can store electric energy, such as Filtering, resonant circuit and moving phase. Different capacitors have different abilities to store energy, which is due to the difference of capacitance. Capacitanceis the ability

2、 of acapacitorto storechargein anelectric field, it is also a measure of the amount ofelectric potential energystored (or separated) for a givenelectric potential. This report is going to investigate the capacitance of a capacitor made from the experiment by using different DC methods. Before the ca

3、pacitor made from the experiment is measured, three DC methods will be tested to verify whether these methods are efficient by measuring the capacitance of the known capacitor. In addition, after measuring the unknown capacitor, the whole capacitors will be connected in parallel and the total size o

4、f capacitance will be measured.TheoryCapacitance can be found by using:. This is for two flat plates. As for the formula, C is the capacitance of a capacitor, A is the area of flat plates, d is the distance between the two flat plates, is the permittivity of vacuum, is the relative permittivity. Per

5、mittivity is constant of proportionality that relates the electric field in a material to the electric displacement in that material and relative permittivity isthe ratio of the permittivity of a substance to that of free space or vacuum. Different materials have different relative permittivity, the

6、 behind table includes the relative permittivity of some different material:MaterialAcetaldehyde Acetic Acid Acetic Acid AcetoneAcetone Dielectric Constant21.86.24.120.717.7Source: (The Engineering Tool Box, 2011.)When two capacitors are placed in series, the charge on each plate is of equal magnitu

7、de, so: ; , hence (where Q is the amount of charges on plate and V is the voltage across the capacitor). When a capacitor is charged (V across capacitor): and ( is the initial voltage adding on the capacitor, is a constant and it is 2.718, R is resistance, C is capacitance and is the initial current

8、 flowing through the capacitor). Analogously, when a capacitor is discharged, it flows and .MethodsApparatus:Power supply, leads, ruler, calipers, clips, known capacitor, aluminum foil, cling-film, paper, multi-meter, video camera.Part A: using three different ways to measure the capacitance if the

9、given capacitor.Method1 of part ADiagram1:CapacitorThis method is measuring the increasing voltage of the given resistor while the capacitor is charged. Voltage of the resister is measured by a multi-meter, which is a tool that can measure many quantities such as voltage, current, and resistance. Th

10、e given capacitor has an area(A) of, and the distance(d) is . The V changes very fast, so there needs a resister to slow it down and a camera to record. The voltage of capacitor can be found by measuring the voltage of the resister, as voltage of the capacitor is equal to the output voltage subtract

11、ing the voltage of resistor: . When the loop is connected, using the camera to record the change of voltage. After recording, drawing a graph of the V (V should be the voltage of capacitor and it is equal to ) and t (the time constant) , then using the equation in theory to find RC and C. Table1: Re

12、sult of method 1of part At(time)/sV(voltage of resistor)/vV(voltage of resistor)/vV (output voltage)/v0.000 1.127 0.373 1.500 1.000 1.013 0.487 1.500 2.000 0.963 0.537 1.500 3.000 0.893 0.607 1.500 4.000 0.792 0.708 1.500 5.000 0.778 0.722 1.500 6.000 0.714 0.786 1.500 7.000 0.619 0.881 1.500 8.000

13、0.627 0.873 1.500 9.000 0.578 0.922 1.500 10.000 0.545 0.955 1.500 11.000 0.515 0.985 1.500 12.000 0.479 1.021 1.500 13.000 0.455 1.045 1.500 14.000 0.433 1.067 1.500 15.000 0.406 1.094 1.500 16.000 0.388 1.112 1.500 17.000 0.370 1.130 1.500 18.000 0.350 1.150 1.500 19.000 0.336 1.164 1.500 20.000 0

14、.323 1.177 1.500 21.000 0.307 1.193 1.500 22.000 0.295 1.205 1.500 23.000 0.285 1.215 1.500 24.000 0.272 1.228 1.500 25.000 0.263 1.237 1.500 30.000 0.223 1.277 1.500 37.000 0.178 1.322 1.500 40.000 0.166 1.334 1.500 41.000 0.161 1.339 1.500 46.000 0.143 1.357 1.500 50.000 0.130 1.370 1.500 58.000 0

15、.113 1.387 1.500 64.000 0.103 1.397 1.500 66.000 0.099 1.401 1.500 71.000 0.093 1.407 1.500 77.000 0.068 1.432 1.500 Analysis for the method1Graph 1: this graph is drawn from the result of method 1. Graph2: the standard graph.V (voltage)t(time)/sThe initial voltage () is 1.45V. , when t=RC,=1.45V, s

16、o V=0.91V, from the graph, t=9s when V=0.91V. Therefore, RC is equal to 9, as the resistance of resistor(R) is given and which is , . The capacitance of capacitor is, but here the result is, so the experiment works not well. There are some reasons resulting to the big error between the real value an

17、d experiment value. First of all, comparing the standard graph with the result graph, When time is zero, the voltage also should be zero, however, the voltage of capacitor is not zero as t=0, this is due to the capacitor has some charges in it before the loop is connected. Second, as the data is got

18、ten from the video by eyes, there exists the manmade error. Third, the voltmeter itself is a resistor, this also will cause the error. In addition, when the experiment is operated, the loop is not connected very well and the capacitor has been used. Method2 of part ADiagram2:This method is measuring

19、 the current while the capacitor is charging. The way of method 2 is same as method 1and the resistor, power supply and capacitor are still the same. First, using the camera to record data. Then, drawing a graph according to these data. Last, calculating the capacitance according to the graph. For t

20、his method, the formula is (is the initial current flowing through the capacitor).Table2: Result of method 2of part At(time)/sI(current)/A0.0005.5101.0002.6502.0001.3403.0000.6874.0000.4205.0000.2226.0000.1407.0000.0988.0000.0649.0000.04310.0000.02711.0000.01912.0000.01413.0000.01114.0000.00915.0000

21、.00716.0000.00620.0000.00426.0000.00234.0000.001Analysis for the method2Graph 3: this graph is drawn from the result of method 2. The relationship between the current and time is. When t=RC, , the initial current() is 5.51A, so I=2.03A. From the graph, the time (t) is 1.7s when I=5.52A. As t=RC, so

22、RC=1.7,. The capacitance of capacitor is. Comparing the result and the real capacitance, this method works well. However, there are still some errors which are cannot be avoided. For example, the data gotten from the video is not accuracy.Method 3 of part ADiagram3This method is measuring the voltag

23、e while discharging. Similar to the method1 and 2, this method is also using camera to record the data and drawing a graph, then, using the graph and formula to get the capacitance of the capacitor.Table3: Result of method 3of part At(time)/sV(voltage of capacitor)/v0.0001.1451.0000.6892.0000.5213.0

24、000.4414.0000.3835.0000.3026.0000.28211.0000.21020.0000.14537.0000.09255.0000.06274.0000.05390.0000.041120.0000.030160.0000.021200.0000.012Analysis for the method3Graph 4: this graph is drawn from the result of method 3.When a capacitor discharged: . =1.145V, When t=RC, . From the graph, t=3s as V=0

25、.421V, SO RC=3, . The real capacitance is , comparing the result with the real, the result is not accuracy. There are also some errors exist, the first is the there is some current flowing through the voltmeter which was ignored. The second is when the data recorded by eyes, there must be some manma

26、de errors. Part B: Making a capacitor This part is describing the process of making a capacitor by using cling-film and aluminum foil. First of all, putting cling-film on the desk and spreading it. Second, laying the aluminum foil on the cling-film tidily. Then, putting the cling-film above the alum

27、inum foil again. The next, letting the aluminum on the top and make sure the two aluminum cannot touch each other. At last, rolling them carefully and using multi-meter to test whether there is current between the two aluminum foils for one meter a time. After rolling, the capacitor was made. The le

28、ngth of materials is 4 meters with a wide of 0.25 meters, so the area (A) is 1 meter square. The distance (d) between two aluminum foils is which is measured by a calipers. If the capacitor needs to store more charge, the area should be larger and the distance should be smaller.Part C: Measuring the

29、 capacitance of the capacitor made in class. Method 1 of part C:Diagram4:This part is going to Estimate the size of the capacitor (capacitance) which was made in class by using four methods. This method is measuring the capacitance by using a known capacitor and let them in series. The formula is ,

30、, The voltage of capacitor 1 gotten from the experiment is 3.45v, the output voltage is 20v ,so , The result . In addition, , A is and d is , therefore, . This result is reasonable and there are some errors exist. First, when the loop is connected, the capacitor will be charged and the data on voltmeter will change, so reading the initial data of the voltmeter(which was used as ) is not accuracy. Second, the power supply has interval resistance, so the voltage of capacitor 1is not equal to absolutely.Method 2 of part C:Diagram5Capa