Designing of Virtual Experiments for the Physics Class

Transcription

1 Designing of Virtal Experiments for the Physics Class Marin Oprea, Cristina Miron Faclty of Physics, University of Bcharest, Bcharest-Magrele, Romania Abstract Physics laboratories have their limitation with respect to eqipment and measrement devices. In sch circmstances, when the necessary technical resorces are not available, some experiments are mch harder to perform. The ones which can be performed are limited in terms of setp and the extent of concrete qantitative measrements. The soltion to overcome these problems resides in the development of a virtal physics laboratory. Virtal instrmentation enables the setp of experiments that can cover a wide range of sitations, complementing the domain of real experiments. In this article we will illstrate the creation of a virtal experiment for the determination of physical qantities sing both the graphical programming environment abview and the application MS Excel. Or focs was laid on the lesson Alternative Crrent Series Circit RC, where we calclated and graphically represented the following physical qantities, depending on the freqency of the circit power sorce: crrent (I), voltage (U), reactance (X, XC), impedance (Z) and phase shift (φ). Keywords: virtal experiment, series circit RC, Excel, abview 1. Introdction Recent stdies in the field of physics edcation (Garabet et al, 2011; Mntean and ogofăt, 2003) have shown that the holistic approach of physics experiments reqires the inclsion of virtal instrmentation in their design and analysis. In sch circmstances, setting p a virtal laboratory becomes imperative, as it wold help extend the possibilities of a real laboratory which has a limited set of measrement and control instrments. In this paper we offer an example for designing a virtal experiment in the field of Electricity The stdy of an alternative crrent series circit RC, where we configred the necessary virtal instrments with the applications Microsoft Excel and abview. 2. Experimental design in Excel From the Office Site, MS Excel is the application which is based on table data. The application is commonly sed in the physics class in order to process experimental data and store it in measrement tables. However, another way of sing this application resides in designing virtal experiments, like the one we focsed on in this paper. We will now describe the stages of the virtal experiment associated with the stdy of the alternative crrent series circit RC. To start with, we opened the application MS Excel and, on the first worksheet (Sheet 1), we inserted the title of the virtal experiment to be ndertaken: The Stdy of a RC Series Circit. From the Insert tab, we clicked on Shapes and selected a rectanglar shape with rond edges. On top of it we inserted other shapes in order to represent the symbols for electric circit components which are part of a RC series circit. In a grop of cells next to the representation of the circit we introdced the mathematical expressions associated with the circit reactances (X si XC), impedance (Z), resonance freqency (r) and the crrent going throgh the circit depending on the impedance (I).

2 248 University of Bcharest, Faclty of Psychology and Edcational Sciences Figre 1. Creating the Excel virtal experiment We associated incrementation bttons to the variable physical qantities (U, R,, C). In order to insert them into the worksheet we selected the Developer tab and from the Ribbon we clicked on Insert and from Form Controls we selected the Spin Btton. Figre 2. Creating Form Controls for the variables Throgh Drag and Drop the bttons associated with the circit variables were introdced in the worksheet, in the cells sitated next to the vales for the variables. The formatting of each btton was performed by right clicking on its symbol, selecting Format control and in the opened window click on the Control tab. We selected Cell ink and by clicking on the arrow on the right hand side of the dialoge window, in the newly opened window we introdced the address of the cell in which the crrent vale of the variable wold be displayed. By clicking OK, the dialoge window closed and the new setting became active. Figre 3. Formatting variable controls

3 The 8 th International Conference on Virtal earning ICV We introdced in a grop of contigos cells (on the same row) the symbols of the physical qantities to be stdied and in the area sitated nder these physical qantities the calcls of their vales. In the colmn associated with the physical qantity f freqency we introdced vales in the interval [0,1000], in order to draw the charts X =X (f), X C =X C (f), I=I(f). We introdced, with the help of control bttons, vales for the voltage U, the resistance R, the indctance and the capacity C. Once the first vales for X, X C, Z și I were calclated, we completed the series of data from the colmns by moving the pointer of the mose over the area corresponding to the chosen freqency domain. Figre 4. Calclated vales Drawing the graphics went according to the following seqence: we clicked on the Insert tab from the Ribbon and inserted a Scatter chart (XY Chart). Once the chart appeared in the diagram, we formatted the srface of the diagram, its axes, the data series from the graphic and the title of the diagram. The following figre (Figre 5) displays a few graphics drawn starting from the following set of vales: U=12V, R=10Ω, =40mH, C=30μF. Figre 5. Reslted graphs for the vales indicated on the right For the vales of the previosly selected circit components, the resonance freqency of the circit was sitated arond the vale of 145 Hz. This is easily noticeable in the graphical representation I I( f ) :

4 250 University of Bcharest, Faclty of Psychology and Edcational Sciences Figre 6. Graphical representation I=I(f) Figre 7. Graph vales 3 Experimental design in abview abview is a graphical programming environment which can be sed in physics edcation for the design of didactic materials of otstanding qality. The wide array of instrments it holds allows for the virtal experiments ndertaken with this application to cover all the fields of physics. The graphical programming environment abview has two windows a Front Panel for the ser, where all the graphical strctres associated with experimental modelling are placed and a window called Diagram, where the logical scheme of the application is to be fond. In order to setp a virtal experiment for the stdy of the alternative series circit crrent RC sing abview we performed the following seqences. On the Front Panel we introdced a grop of controls for the vales of the physical qantities to be stdied: freqency, voltage U, resistance R, indctance and capacity C. Every control had a specific label attached and a digital display type of btton for a precise display of the vales of the measred physical qantity. Moreover, we placed a WAVEFORM GRAPH diagram on the Front Panel in order to visalise the graphs of the the instantaneos qantities of: the crrent throgh the circit: i i(t) the voltage on the resistor: the voltage on the coil: the voltage on the resistor: R C R (t) C (t) (t) We have to specify the fact that this type of GRAPH does not accept individal (scalar) vales, bt only rows of vales (ARRAY). In addition, we inserted on the Front Panel two more diagrams in order to visalize the freqency dependence of the effective vales of the crrent and of the reactances: X X ( ) I I( ) X,, C X C ( ). On the right hand side of the Front Panel we placed the indicators for the display of the vales of the physical qantities: impedance Z, phase shift X, X, reactive impedant vales C, U maximal vales for voltage ( max I ) and crrent ( max U ), actal vales R, U, UC, resonance freqency rez, qality factor Q. All these physical qantities are placed in relation to specific measrement nits.

5 The 8 th International Conference on Virtal earning ICV The diagram of the application is based on two formlae nodes, each inclded in a FOR loop, a repetitive strctre with a fixed nmber of iterations (in this virtal experiment there were 100 and 1000 iterations for each loop). In order to watch the vale shift of the physical qantities in real time, the two FOR loops were integrated in a WHIE loop. This is a repetitive strctre with a conditional terminal. The WHIE loop exectes non-stop the part of the diagram it contains ntil a stopping condition of the process appears, a logical vale TRUE. The simlatenos display of the graphics for the instantaneos physical qantities was done by concatenating the array of vales taken at the exit of a FOR loop by a BUID ARRAY element, connected to a WAVEFORM GRAPH. The array of vales Figre 8. Front Panel obtained at the exit of the second FOR loop were assambled in the form of clsters throgh BUNDE fnctions and concatenated throgh a BUID ARRAY element, which sent them to a XY chart. Figre 10. The diagram of the abview application In the following figres one can observe the reslts of an experimental simlation based on this project. Figre 8. Graph 1

6 252 University of Bcharest, Faclty of Psychology and Edcational Sciences Figre 8. Graph 2 Figre 8. Graph 3 4 Conclsions A teacher can se abview and Excel to design classical virtal physics experiments, bt also experiments which are qite hard to realize with the instrments of a standard laboratory. Designing virtal experiments is both a challenging and pleasant activity. The reslts give both the teacher who designs them and the stdents who easily perform them a high degree of satisfaction. From a didactic point of view, the graphical interfaces containing the virtal instrmentation create a pleasant atmosphere for the stdents and allow them to get sed to the manner and rigors of scientific work. Introdcing virtal experiments in the physics class takes the didactic process to a whole new level of variety and nderstanding, desired by both teacher and stdents. All in all, the virtal instrmentation provided by abview and Excel is able to give the classes a high qality level in terms of homogenity, integrality and diversity. References Benacka, J. (2009): Simlating Projectile Motion in the Air with Spreadsheets, Spreadsheets in Edcation (ejsie), 3, 2, available at: ed.a/ejsie/vol3/iss2/3 [ ]. Cotfas, P.; Ursti, D. and Samoilă, C. (2000): Creating a Virtal ab Using abview, Proceedings of TICE 2000, available at: 3concept/012cotfa.pdf [ ]. Garabet, M., Miron, C., Neacş, I. (2011): Remote Experiments in Moisil E-lab. In Proceedings of the 6th International Conference on Virtal earning ICV, Mntean, M. and ogofăt, B. (2003): Virtal Instrmentation abview, Bcharest: Credis Pblishing Hose. Prcell, E.M. (1982): Eletricity and Magnetism. Berkley Physics Corse, vol.2, Bcharest: Didactic and Pedagogic Pblishing Hose. Rajpt, A.K. (2013): Simlation of R--C Series and Parallel Resonance in Basic Electrical Engineering with abview, Research Jornal of Engineering Science, 2(1),