Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation in PUC/SP and the development of experimental activities in Physics using the Classmate PC
Sound Spectrum
Lesson Plan
Author: Prof. Alessandro Washington Daniel (E.E. José Chaluppe)
11th grade students from E.E. José Chaluppe Bruna Alves Freires Teixeira Oscar Hugo Lunguinho Falchetto Jonny Antunes Machado
Supervision Prof. Marisa Almeida Cavalcante (PUC/SP) e Prof. Cristiane Rodrigues Caetano Tavolaro (PUC/SP)
July 2009
PontifĂcia Universidade CatĂłlica de SĂŁo Paulo Junior Scientific Initiation in PUC/SP and the development of experimental activities in Physics using the Classmate PC
Introduction The purposes of Physics teaching in High School indicate as objectives to take the students to understand the concepts, procedures and physical strategies that allow them to develop subsequent studies and to acquire general scientific formation, applying their knowledge to several situations, using them in the interpretation of Science, in technological and in daily activities. It is important to recognize that the pupils have the intention to learn, but perhaps not what the school currently intends to teach them. That is, the education project many times has little to see with the learning project. Thus, what Physics must search in high school is to assure that the inquiry ability rescues the inquiry spirit, the desire to know the world we inhabit. Not only in a pragmatic way, as immediate application, but expanding the understanding of the world, in order to consider new questions and, perhaps, to find solutions. It is in that perspective that we propose this activity in that specific contents related to Acoustic Physics will be approached, so that to understand a little more "how things work." Through this Kit it will be possible to establish assemblies, that will allow us to study in detail the resonance phenomena in resonant tubes, The sound wave generators and the resonant spectra analyzers are obtained from shareware versions and free from softwares. Several measures can be made from the determination of the speed of the sound to detailed studies of different resonant spectra in multiple experimental conditions such as open tube, closed tube in one of the extremities, in both extremities and different lengths. All activity was articulated in a way to make possible to develop competences and abilities as: To understand that tables, graphs and mathematical expressions can be different forms of representation of a same relationship, with potentialities and own limitations, to be able to choose and to make use of the most appropriate language in each situation, besides translating the meanings of those several languages amongst themselves. To elaborate analytical reports, presenting and discussing data and results, be of experiments or of critical evaluations of situations, making use, whenever necessary, of the appropriate physical language.
PontifĂcia Universidade CatĂłlica de SĂŁo Paulo Junior Scientific Initiation in PUC/SP and the development of experimental activities in Physics using the Classmate PC
Objectives This work has as objective presenting some experimental resources developed to understand topics of Waves and Acoustics and specially determine the speed of sound. Besides the innovative methodology, we can highlight the versatility of the high technology equipment and low cost. On the other hand, those resources allow a simple assembly and easy handling
Content The contents approached in this activity make possible to treat the following structuring themes: Sound waves, image and communication treated in the 11th grade of High School. Standards and Structuring Themes
This activity can be done in the 11th grade of High School
Structuring Theme 4: Sound, Image and Information (11th grade) To place yourself in the contemporary world it is necessary to understand the current communication means and information that have in their base the production of images and sounds, their reception processes, their codes and registration forms and the re-establishment of their signals in the receiving devices. To study those mechanisms means to propitiate competences to understand, to interpret and to deal in an appropriate way with technological apparatuses, like television, Cd and DVDs players, the computer, the movies or even photography.
Activity RESONANT TUBES
The system of resonant tubes allows us to take measures of speed of the sound in the air, measures of wavelengths through formation of observable stationary waves with cork powder
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation in PUC/SP and the development of experimental activities in Physics using the Classmate PC inside of the tube or through the harmonic components that integrate the resonant spectrum of the resonance tube. SOUND WAVES IN TUBES
The sound is a longitudinal mechanical wave, in other words, it needs a medium to spread and its propagation has the same direction that the disturbance that caused it. The sound wave spreads through air creating compression and rarefaction areas in the medium. The operation principle of most of the wind instruments is the production of stationary sound waves inside the tubes (known as tube of Kundt). Only waves with certain frequencies are reproduced that are called natural frequencies of vibration, similar to the frequencies that can exist in a vibrating cord. The possible stationary waves that are formed inside of a tube of length L, for instance, with one closed extremity can be studied from the procedure proposed in this experiment.
Calculating the speed of sound
Number of classes needed for the activity: 4 classes
Materials used and its operation Classmate PC Speaker
tube
Cork powder
microphone
Figure 1: General view of the assembling.
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation in PUC/SP and the development of experimental activities in Physics using the Classmate PC First Class
- To explain the objective of the experiment, its relationship with the daily life - To present the material used to accomplish the experiment; - To explain the operation of each one of the materials.
a) Classmate PC, its function is to receive signals through the sound board and to send it to the software.
Figure 2: Classmate PC that will be used in the data collection.
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation in PUC/SP and the development of experimental activities in Physics using the Classmate PC
Figura 3: Tube that will be used.
b) Tube of Kundt, it is used to put the cork powder and reception of the sound for analysis. c) Cork powder is used for visualization of the resonance in the resonant tube.
Figure 4: Cork powder
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation in PUC/SP and the development of experimental activities in Physics using the Classmate PC d) speakers, they are used for sound emission.
Figure 5: connected to the Classmate PC.
Speaker
a) microphone, it is used to capture the sound.
Figure 6: Microphone to capture the sound produced in the tube.
Second class
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation in PUC/SP and the development of experimental activities in Physics using the Classmate PC ASSEMBLY OF THE EXPERIMENT - To set up the experiment; - To do demonstrations; - To hypothesize.
1. To turn on the Classmate PC and to access the software Gram v6 *
Figure 7: Classmate PC screen showing Gram V6.
1)
Connect the microphone to the Classmate PC sound board
Figure 8: Connecting the microphone to the Classmate PC.
3) Get a 50 cm Kundt tube.
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation in PUC/SP and the development of experimental activities in Physics using the Classmate PC
Figure 9: Kundt Tube.
Third class
ACCOMPLISHING THE EXPERIMENT - Assembly and experimentation; - Analysis to elaborate the calculation; - Calculating the speed of the sound. 1) We connected the microphone to the Classmate PC with software Gram-v6 opened
Figure 10: Connecting the microphone to the Classmate PC and capturing the sound in the tube.
2) We leave the microphone close to the tube.
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation in PUC/SP and the development of experimental activities in Physics using the Classmate PC
Figure 11: Microphone close to the tube.
3) According to the illustration hit hard the extremity of the tube, producing the sound.
Figure 12: Hitting the extremity of the tube.
4) Through the Software Gram-v6 *, we analyze the frequency spectrum.
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation in PUC/SP and the development of experimental activities in Physics using the Classmate PC
Figure 13: Analyzing the frequency spectrum. To have access to the software go to: http://www.elektrosmog.de/Software/gram6.exe or
http://xviiisnefnovastecnologias.blogspot.com/2009/08/software-de-analisesonora-gram-v6.html
5) The stationary wave of smaller frequency that is formed, is also called fundamental wave, corresponds to the largest possible wavelength in this tube. The illustration shows the air movement inside the tube. It is noticed that the displacement of the air molecules that are close to the closed extremity of the tube is zero (knot) and that the maximum displacement happens in the open extremity. The Java* simulation that produced the illustration integrates the work methodology adopted in the study of the resonant tube. The wavelength in this case is related to the length L of the tube by
L≡ or
λ 4
λ ≡ 4 .L and the oscillation frequency can be calculated by
f ≡
v
λ
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation in PUC/SP and the development of experimental activities in Physics using the Classmate PC Therefore:
f ≡
v 4 .L
* For more information on Java on longitudinal waves access: http://www.walter-fendt.de/ph11br/stlwaves_br.htm
Closed tube in one extremity
Figure 14: it shows the maximum displacement of the air particles in the open side and representation of the corresponding opening. On the closed side, a knot of displacement of particles http://www.walterfendt.de/ph11br/stlwaves_br.htm.
6) We calculate the speed of sound using the following formula:
f ≡ Where:
v 4 .L
- f : frequency - v : velocity - L : tube length
Fourth Class
Calculation and analysis Visualization of the resonance with cork powder
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation in PUC/SP and the development of experimental activities in Physics using the Classmate PC Calculations The experiment was accomplished with a frequency registered by the software of 175 Hz in the first possibility (knot), where the measure of the tube was of 50 cm of length and 3cm of diameter.
v f ≡ 4 .L
Using the formula
Data:
F = 175 Hz V = We will find out L = 50 cm
Therefore:
v 175 = 4.50 v = 175 .200 v = 35000 cm s
Students report: The speed of sound is calculated in m/s, then we transformed 35000 cm/s in 350 m/s. the speed of the sound propagates with a speed of 340 m/s at 15°C. That was what tried to prove. But the objective is to get to a value that is as close as possible. Visualization of the resonance with cork powder For this visualization we will consider an open tube in the two ends and through the available simulation at http://www.walter-fendt.de/ph11br/stlwaves_br.htm fastens the length of the tube to 50 cm and verify the frequency to obtain the 1st harmonic:
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation in PUC/SP and the development of experimental activities in Physics using the Classmate PC
Fig.15: frequency observed for the fundamental frequency of the tube equal to 344 Hz.
Now position the speaker in front of the tube and using the signal generator software connect the sound port of the classmate PC to the speaker. Put the cork powder inside the tube and spread along all its length. Fasten in the generator the frequency in about 344 Hz and vary this value (start for instance with 320 Hz and increase gradually) and observe the cork powder. There will be a value for which the powder will vibrate (only in the ends of the tube). This value for which the vibration is its maximum correspond the resonance frequency of the tube, open in the two ends.
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation in PUC/SP and the development of experimental activities in Physics using the Classmate PC
Figure16:
Image
of
the
signal
generator
screen:
to
download,
the
address
is
http://xviiisnefnovastecnologias.blogspot.com/search/label/Sine%20Wave%20Gene rator
When that happens we have: Like this, we can also obtain the value of speed of propagation of the sound where: F. frequency obtained for the resonance condition L. length of the tube
Figure 17: Image in that the resonance is observed for the open tube in the two ends.
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation in PUC/SP and the development of experimental activities in Physics using the Classmate PC
To think!! 1) If we increase the size of the tube will you expect to obtain a frequency of resonance larger or smaller than the obtained value? *
2) The value obtained for the speed of sound can be corrected depending on room temperature? *
*Access the link and check!!!! http://www.cepa.if.usp.br/e-fisica/apoio/textos/a10.pdf
Links •
http://picintel-profalessandro.blogspot.com : Blog of the project where you will find more details concerning the experiment. • http://picjrintelpucsp.blogspot.com/: Blog of the program of the Junior Scientific Initiation of PUC/SP in partnership with Intel • http://xviiisnefnovastecnologias.blogspot.com/search/label/velocidade%20do%20s om : Link to access to information on the acoustics kit. • http://www.cepa.if.usp.br/e-fisica/apoio/textos/a10.pdf: Link to the article about the determination of the speed of sound published in Physics in the School
• Sound spectrum analyzer: Gram V6. Author: Philip Van Baren www.monumental.com/rshorne/gram.html or http://xviiisnefnovastecnologias.blogspot.com/2009/08/software-de-analisesonora-gram-v6.html • Java simulation. Longitudinal waves. Author: Walter Fendt www.walter-fendt.de/ph11br/stlwaves_br.htm • Signal generator http://xviiisnefnovastecnologias.blogspot.com/search/label/Sine%20Wave%20Gen erator
Pontifícia Universidade Católica de São Paulo Junior Scientific Initiation in PUC/SP and the development of experimental activities in Physics using the Classmate PC
Reference • (PCN) - Parâmetros Curriculares Nacionais Ensino Médio – Parte III – Ciências da Natureza, Matemática e suas tecnologias, Apresentação pag. 203 à 218 e Conhecimentos em Física pag. 229 à 237. CAVALCANTE, M. A. e TAVOLARO, C. R. C. Medindo a Velocidade do Som. A Física na Escola (suplemento da RBEF) v.4 n.1, maio de 2003. • http://www.cepa.if.usp.br/e-fisica/apoio/textos/a10.pdf • BARBETA, V. B. e MARZZULLI, C. R. Experimento Didático para Determinação da Velocidade do Som no Ar, Assistido por Computador. RBEF vol. 22 no 4, dezembro de 2000. OLIVEIRA, L. M.; VEIT, E. A. e SCHNEIDER, C. Site: Novas Tecnologias no Ensino de Física http://www.if.ufrgs.br/cref/ntef/index.html