Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation PUC/SP and the development of experimental activities in Physics using the Classmate PC
Determination of the electrical net frequency
Lesson Plan
Author: Prof. Júlio Lamon (Escola Nossa Senhora das Graças) 11th grade students from Nossa Senhora das Graças School Alexandre Portugal de Almeida Giuliane Roncoleta Yunes
Supervision Prof. Marisa Almeida Cavalcante (PUC/SP) and Prof.Cristiane Rodrigues Caetano Tavolaro (PUC/SP)
July 2009
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation PUC/SP and the development of experimental activities in Physics using the Classmate PC
Introduction To build a vision of the Physics that is pointed towards a contemporary citizen's formation, capable to understand, to intervene and to participate in reality, We propose an activity based on the National Curriculum Parameters (PCN+). The activity is based on the structuring theme "electromagnetic equipments and telecommunications", so that the students will deepen their knowledge on: electric current, resistor, Ohm's Law, generator and continuous and alternate current production. The phototransistor will allow the teacher to introduce modern physics content, as well as to discuss the impact provoked by the development of electronics in the last century, because this fact is related with an important competence: "To recognize and evaluate the contemporary technological development, its relationship with Sciences, its role in the human life, its presence in the daily world and its impact in the social life." Other competences developed by the students should be: •
" To recognize and to use appropriately, in writing and orally, symbols, codes and nomenclature of the scientific language";
•
" To elaborate oral or written communications to tell, analyze and to systematize events, phenomena, experiments, subjects, interviews, visits, correspondences";
•
" To recognize, use, interpret and propose explanatory models for phenomena or natural or technological systems";
The students will have to explain the procedure and the operation of the experiment elaborating texts in form of lab reports. And still: •
" To identify in a given problem situation the information or your relevant variables and possible strategies to solve it";
•
" To identify natural phenomena or magnitudes in a given domain of the scientific knowledge, to establish relationships; identify regularities, controlled variables and transformations";
•
" To select utilize measuring and calculation instruments, present data and use scales, do estimates, elaborate hypotheses and interpret results";
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation PUC/SP and the development of experimental activities in Physics using the Classmate PC •
" To consult, analyze and interpret texts and Science and Technology communications transmitted by different means.
When doing the experiment the students will be; setting up the circuit, identifying the measuring instruments, the Physics magnitudes involved in the experiment, which magnitudes possess constant or varied values, proposing explanations for the phenomena observed at the same time in that they will be researching and doing calculations and tables. It's worth it to emphasize that the experiment produces an enormous variety of actions for the student's learning, besides, it gives the teacher the opportunity to become a researcher.
Objectives To understand the alternating current concept through experimental activities that use high technology electronic components, but lower costs and computers as instruments of data collection.
Content
The content approached in this activity allows us to treat the following structuring themes in agreement with the Standards the State of São Paulo: Sound, image and communication - 11th grade Light: sources and physical characteristics Electromagnetic waves Electromagnetic transmissions Electric equipments, Matter and Radiation - 12th grade Electric circuits Fields and electromagnetic forces Generators Production and electric power consumption Matter: their properties and organization
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation PUC/SP and the development of experimental activities in Physics using the Classmate PC Atom: emission and radiation absorption Electronics and computer science
According to the specific content the teacher should explain: - The operation of incandescent and fluorescent light bulbs, observing the use and the characteristics supplied by the manufacturer. - The model of electric current and the resistive systems - Ohm's Law. - Faraday's Law of induction - Operation of the electric generators and transformations of energy to obtain the electric power - The economical and technological development due to the use of electric power - Rutherford and Bohr's atomic models of matter. - The absorption and the emission of the radiation by matter, Plank's Law and the duality wave-particle. - The semiconductor model and its use in the electronic components. - The economical and technological development due to the use of the electronic components.
Curriculum and structuring themes This activity can be worked in the 11th and 12th grades, although for the 11th grade students the teacher will need to do introduce the structuring theme Electric equipments, Matter and Radiation.
Material A mounted circuit in series using: a 680 ohms resistor, a phototransistor, a 9 V battery and a LED. A laser point, an incandescent light bulb, a luminescent light bulb, two alligator clamps, wires, sound plug for the sound board of The Classmate PC, data analysis software, battery connector and flashlight.
Activity Number of classes needed for this activity: 5 clasess
1st class
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation PUC/SP and the development of experimental activities in Physics using the Classmate PC This class will be divided into two stages. 1 - In this class we will explain the circuit and its components, the function and operation of each component. It is necessary that the teacher explains the operation of the phototransistor, reminding that the incidence of light (photons) provokes an increase of current, this increase of current is proportional to the intensity of the incident light. Instructions 1.1 Connect in series the LED, the 680 ohms resistor and the 9 V battery.
Fig. 1: Series circuit: Battery, resistor and LED.
1.2 Verify the LED’s polarity (it has to turn on). 1.3 Connect the group LED-resistor-battery of 9 V in series with the phototransistor.
Fig. 2: Series circuit: Batery, resistor, LED and phototransistor.
Be careful with the correct polarity of the phototransistor and the LED, so that if the phototrasistor is illuminated the laser pointer the LED turns on.
PontifĂcia Universidade CatĂłlica de SĂŁo Paulo Junior Scientific Initiation PUC/SP and the development of experimental activities in Physics using the Classmate PC
Fig. 3: Laser pointer
1.4 Connect the cable with the alligator clamps and the connector for the Classmate PC in parallel with the resistor's terminals (the clamps on the terminals of the resistor).
Fig. 4: Alligator clamps in parallel with the resistor.
1.5 The sound connector for the Classmate PC has to be plugged in the mic entrance (pink).
Fig. 5: Plug connection in the microphone entrance of the Classmate PC.
1.6 Connect the light bulb (incandescent or fluorescent) to electricity put the phototransistor in front of the lit light bulb. 1.7 The circuit should be set according to the illustrations below
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation PUC/SP and the development of experimental activities in Physics using the Classmate PC
Fig. 6: Complete set up of the equipment.
Fig. 7: Diagram of the equipment.
Function and operation of each component: •
LED detects if the circuit is working correctly
•
9 V Battery feeds the circuit.
•
The light bulb (incandescent or fluorescent) linked to the electric net will be turning on or off according to the frequency of the electric net, in our case 60 Hz.
•
The phototransistor will detect when the light bulb (incandescent or fluorescent) is lit or extinguished; when the light bulb is lit, it produces an increase of electric current in the circuit, when the light bulb is turned off the electric current in the circuit returns to its original value.
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation PUC/SP and the development of experimental activities in Physics using the Classmate PC •
680 ohms resistor detects the variation of the electric current and DDP on their terminals, as the resistor is connected with the classmate PC, this variation of DDP is sent to the entrance of the classmate PC and shown by the Audacity or Oscilloscope software.
It fits here a more detailed explanation on the electronic component that will have a fundamental role in the experiment. The phototransistor is a semiconductor, that is, a solid formed by covalent bonds, that produce a crystalline net (its atoms are distributed in a geometric way). That way there are no free electrons, therefore a semiconductor doesn't conduct an electric current. However it is possible to introduce sludges in its crystalline net and this process is called dopage. Admit that initially a solid is formed by silicon or germanium atoms. If we introduce atoms that possess five valence electrons (arsenic, for instance) in this solid we will have a dopage type N, Germanium and Silicon have four valence electrons, thus, Arsenic electrons (donor) it is a negative charge bearer, the fifth electron of the Arsenic can be used to produce electric current. If we introduce atoms that possess three valence electrons (aluminum, for instance) in this solid we will have a dopage type p, aluminum has three valence electrons and Germanium and Silicon have four valence electrons, therefore, Aluminum (Acceptor) is a positive charge bearer, type P, the gap (There is an electron missing in the orbital) can be used to produce electric current, since the electron can occupy this gap. Forming a semiconductor with type P and type N, we can obtain movement of charge bearers.
Observe that in the illustration the electron of the Arsenic atom can move to occupy the gap of the Aluminum, but this doesn't happen until the electron receives a minimum amount of energy. The electron of the Arsenic is in the valence band, when
PontifĂcia Universidade CatĂłlica de SĂŁo Paulo Junior Scientific Initiation PUC/SP and the development of experimental activities in Physics using the Classmate PC receiving this minimum amount of energy (E = h.f) it passes to the transport band and only now it can move to the gap of the Aluminum.
The phototransistor is formed by three pieces of PNP semiconductors. The base will be formed by dopage N that have electrons that can move, since they receive the corresponding amount of energy, a light photon will supply the amount of minimum energy for the electrons to pass to the transport band. In the presence of the light photons we will have more electrons in the transport band, therefore an increase of the electric current. In the absence of the light photons we won't have electrons in the transport band, therefore a decrease of the electric current. Observe that the phototransistor is a sensor of light, the larger the intensity of it, the larger the electric current will be. The collector and the emitter will be formed by dopage P, it has gaps that can receive electrons.
2 - Show the difference between the curves obtained when the lamp is fed by electricity and when it is fed by a flashlight. It is very important to emphasize this difference. Initially we will learn how to use the Audacity and Oscilloscope software.
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation PUC/SP and the development of experimental activities in Physics using the Classmate PC Inicialmente vamos aprender utilizar os softwares Audacity e Oscilloscope.
2-1 Using the Audacity software (http://audacity.sourceforge.net/download /), observe the illustration below.
Fig. 8: Audacity software screen showing how to measure the period.
2.2
Using
the
Oscilloscope
software
http://polly.phys.msu.su/~zeld/oscill.html
http://www.if.ufrgs.br/tex/fis01043/MCL_down.html, observe the illustration below.
or
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation PUC/SP and the development of experimental activities in Physics using the Classmate PC
Fig. 9: Oscilloscope software screen showing how to measure the period.
2.3 - With the incandescent light bulb fed by electricity to obtain the curve with both software: Audacity and Oscilloscope.
Fig. 10: Oscilloscope software screen showing the measure of the signal obtained with the incandescent light bulb.
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation PUC/SP and the development of experimental activities in Physics using the Classmate PC
Fig. 11: Audacity software screen showing the measure of the signal obtained with the incandescent light bulb.
Students should be questioned on the reason of that result.
2.4 With a flashlight fed by a battery obtain the curve with the both software Audacity and Osciloscope.
Fig.12: Outline of the equipment with the flashlight instead of a light bulb.
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation PUC/SP and the development of experimental activities in Physics using the Classmate PC
Fig 13: Screen of the Audacity software showing the measure of the signal obtained with the flashlight.
Fig. 14: Screen of the software Oscilloscope showing the measure of the signal obtained with the flashlight.
The student should notice that the curves don't have a period, they are practically a straight line. 2.5 - With the fluorescent light bulb fed by electricity to obtain the curve with both software Audacity and Osciloscope.
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation PUC/SP and the development of experimental activities in Physics using the Classmate PC
Fig. 15: Screen of the software Oscilloscope showing the measure of the signal obtained with the luminescent light bulb.
Fig. 16: Screen of the software Audacity showing the measure of the signal obtained with the luminescent light bulb.
2.6 - Students should write down their observations and explain the differences between the light bulbs fed by electricity and fed by battery. The question that should be made with the students: when we observe the light emitted by light bulbs connected to electricity, incandescent and luminescent and others connected to a battery (in flashlights), did we notice a difference in brightness, besides the intensity difference? How is it possible then to explain the differences obtained through the experiment? 2 º class
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation PUC/SP and the development of experimental activities in Physics using the Classmate PC 1 - This class is reserved for the students to come up with hypotheses to explain the curves found. Why does electricity produce a different curve type from the curve of the battery? 1.1 - the teacher should access the site http://phet.colorado.edu/sims/circuit-constructionkit/circuit-construction-kit-ac_pt.jnlp and make the simulations represented in the illustrations below:
1.2 - Students should understand the relationship between the simulations and the curves found and propose an explanation. It is important to guide the students so that they come up with coherent explanations according to the simulations and the observed curves. At this point the students should notice the relationship between the experimental result and the theoretical model of alternate electric current.
1.3 - With the explanation proposed by the students, the teacher should explain how the alternating current is produced at the power plant, that is the electrons are oscillating in the
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation PUC/SP and the development of experimental activities in Physics using the Classmate PC transmission line, and in the case of the continuous current (produced by the battery) this oscillation doesn't happen.
2 - Explain the calculation of the frequency of the electric net. 2.1 - In the curves obtained with the light bulbs fed by electricity, measure the time between two consecutive points of same phase (we can take the two maximum points of the curve). This time will be the period. We then determine the frequency
frequência =
1 período
2.2 - The teacher should notice that the measured period is the interval of time where the light bulbs are lit. However we want the interval of time in which the lamps are lit and extinguished. Thuss the found frequency should be divided by two.
For classes 3 and 4 the teacher can use Microsoft Excel to make the calculations and tables. The author used this software, because it is practical and it puts the students in contact with some of its basic concepts.
3rd class 1 - In this class we must make the experimental process to determine the frequency of the electric net using the incandescent light bulb and the Audacity and Osciloscope software. Keep in mind the procedures 2.1 and 2.2 from the first class and the procedure 2.2 from the second class.
1.1-Using the incandescent light bulb fed by electricity, to obtain the curve with the Audacity software.
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation PUC/SP and the development of experimental activities in Physics using the Classmate PC 1.2 - Measure the period (minimum of ten measures). Fill out the table below:
Calculate the average frequency the absolute error and the standard deviation.
averagedev iation =
∑ xi − x
2
∑ ( xi − x )
s tan darddeviat ion =
n
n −1
Final result: (60 ± 3) Hz 1.3 - Using the incandescent light bulb fed by electricity, obtain the curve with the Osciloscope software. 1.4 - Measure the period (minimum of ten measurements), Fill out the table below, keeping in mind
that
in
the
Oscilloscope
we
have
to
subtract
the
time
·. Calculate the average frequency, the average error and the standard deviation. Final result: (60 ± 2) Hz
intervals.
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation PUC/SP and the development of experimental activities in Physics using the Classmate PC
4th class 1 - In this class we should experiment to determine the frequency of the electric net using the fluorescent light bulb and the Audacity and Osciloscope software. Keep in mind the procedures 2.1 and 2.2 from class 1 and the procedure 2.2 from class 2.
1.1 - Using the fluorescent light bulb fed by electricity, to obtain the curve with the Audacity software. 1.2 - Measure the period (minimum of ten measures), to fill out the table below.
Calculate the average frequency the average error and the standard deviation. Final result: (60 ± 3) Hz 1.3 - Using the fluorescent light bulb fed by electricity, to obtain the curve with the Osciloscope software. 1.4 - Measure the period (minimum of ten measures), to fill out the table below, keep in mind that in Oscilloscope you have to subtract the intervals of time.
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation PUC/SP and the development of experimental activities in Physics using the Classmate PC
Calculate the average frequency, the error and the standard deviation. Final result: (60 ± 9) Hz
5th class 1 - In this class we have to elaborate the report with the following items: introduction, experimental procedure, results and discussion, conclusion and bibliographical references. 1.1 - Initially the teacher has to comment on two facts: 1.1 a - The frequency of electricity In Brazil is 60 Hz, evidently it is not possible to guarantee that during the experiment this frequency didn't suffer some variation. 1.1 b - During an experiment errors occur, therefore the value found for the frequency of electricity won't be exactly 60 Hz. For that, the final results that show the standard deviation have to be analyzed, and also the reason for the usage of two different software to the data collection and analysis. 1.2 - the report should contain the explanations of the following items: 1.2a - The differences between the curves obtained by electricity and by the battery. 1.2b – How is the electric current produced in the battery and in the generator. 1.2c - Which are the function and operation of the components of the circuit giving special attention to the phototransistor once it allows the teacher to introduce concepts of modern physics.
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation PUC/SP and the development of experimental activities in Physics using the Classmate PC
Links Blog with more information about the experiment http://picjrintelpucsp.blogspot.com/ http://picintel-profjulio.blogspot.com/ Text about analogical-digital conversion http://xviiisnefnovastecnologias.blogspot.com/2009/01/texto-de-orientao-para-oficina-denovas.html Electric circuit simulator http://phet.colorado.edu/sims/circuit-construction-kit/circuit-construction-kit-ac_pt.jnlp Audacity Software http://audacity.sourceforge.net/download/ Osciloscope Software http://polly.phys.msu.su/~zeld/oscill.html Others http://www.sbfisica.org.br/arquivos/PCN_FIS.pdf http://portal.mec.gov.br/seb/arquivos/pdf/CienciasNatureza.pdf http://www.rededosaber.sp.gov.br/contents/SIGSCURSO/sigsc/upload/br/site_25/File/Prop_FIS_COMP_red_md_20_03.pdf
http://www.pucsp.br/gopef
Reference Cavalcante, Marisa Almeida;TAVOLARO,Cristiane .R.C.;BONIZZIA,Amanda ; e PIFER,Anderson. “Novas Tecnologias no Ensino de Física” GOPEF/PUC-SP 2008 .
TAVOLARO, Cristiane. R. C.; e Cavalcante, Marisa Almeida. ”Física Moderna Experimental”. Barueri, Editora Manole 2003.
FEYNMAN, Richard P. “Lições de Física de Feynman volume III”. Porto Alegre, Artmed Editora. 2008.
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation PUC/SP and the development of experimental activities in Physics using the Classmate PC DEUS, Jorge Dias de; PIMENTA, Mário; NORONHA, Ana; PEÑA,Teresa; e BROGUEIRA, Pedro. ”Introdução à Física”. Lisboa, McGraw-Hill 2000.
EISBERG, Robert; e RESNICK, Robert, “Física Quântica”. Rio de Janeiro, Editora Campus 1979.