Determination of the electrical net frequency Lesson Plan

Pontifícia Universidade Católica de São PauloJunior Scientific Initiation PUC/SP and the development of experimental activities in

Physics using the Classmate PC

Determination of the electrical net frequencyDetermination of the electrical net frequency

Lesson PlanLesson 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



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";



" 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

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

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.

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

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.

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.

Fig 8 : esquema

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

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.



Fig 9:bandas

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.



Fig 10 : esquema fototransistor

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.

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. 11: Audacity software screen showing how to measure the period.



- gravar clicar em

- para parar a gravação clicar em

- aplicar zoom clicar em

- selecionar,botão direito do mouse em um ponto de máximo arrastar até o próximo ponto de

máximo ,observe que o intervalo do período já está determinado (retângulo vermelho)

- capturar a tela pressionar a tecla “print screen” no teclado, com o “mspaint” colar e salvar a

imagem em um arquivo qualquer

.

2.2 Uuing the Oscilloscope software http://polly.phys.msu.su/~zeld/oscill.html or

http://www.if.ufrgs.br/tex/fis01043/MCL_down.html, observe the illustration below.

Fig. 12: Oscilloscope software screen showing how to measure the period.

- gravar clicar em

- - para parar a gravação clicar em

- Para determinar o período colocar o ponteiro do mouse no ponto A e anotar o

tempo(retângulo vermelho) em seguida colocar o ponteiro do mouse no ponto B e

anotar o tempo(retângulo vermelho)

- o período o tempo do ponto A menos o tempo do ponto B



CUIDADO QUE OS TEMPOS ESTÃO EM MILI-SEGUNDOS

- capturar a tela pressionar a tecla “print screen” no teclado, com o “mspaint” colar e

salvar a imagem em um arquivo qualquer

2.3 - With the incandescent light bulb fed by electricity to obtain the curve with both software:

Audacity and Oscilloscope.

Fig. 13: Oscilloscope software screen showing the measure of the signal obtained with the

incandescent light bulb.

Fig. 14: 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.15: Outline of the equipment with the flashlight instead of a light bulb.

Fig 16: Screen of the Audacity software showing the measure of the signal obtained with the

flashlight.



Fig. 17: 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.

Fig. 18: Screen of the software Oscilloscope showing the measure of the signal obtained with the

luminescent light bulb.



Fig. 19: 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

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-construction-

kit/circuit-construction-kit-ac_pt.jnlp and make the simulations represented in the illustrations

below:



Fig20: esquema bateria

Fig 21: esquema rede

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

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

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.



1.2 - Measure the period (minimum of ten measures). Fill out the table below:

Fig 22: audacity incandescente

Calculate the average frequency the absolute error and the standard deviation.

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 intervals. ·.

Fig 23: Oscilloscope incandescente



Calculate the average frequency, the average error and the standard deviation.


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.

Fig 24: audacity fluorescente

Calculate the average frequency the average error and the standard deviation.


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.



Fig 25: Oscilloscope fluorescente

Calculate the average frequency, the error and the standard deviation.


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.



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-de-

novas.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/SIGS-CURSO/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.

http://www.pucsp.br/gopef

http://www.rededosaber.sp.gov.br/contents/SIGS-CURSO/sigsc/upload/br/site_25/File/Prop_FIS_COMP_red_md_20_03.pdf

http://www.rededosaber.sp.gov.br/contents/SIGS-CURSO/sigsc/upload/br/site_25/File/Prop_FIS_COMP_red_md_20_03.pdf

http://portal.mec.gov.br/seb/arquivos/pdf/CienciasNatureza.pdf

http://www.sbfisica.org.br/arquivos/PCN_FIS.pdf

http://polly.phys.msu.su/~zeld/oscill.html

http://audacity.sourceforge.net/download/

http://phet.colorado.edu/sims/circuit-construction-kit/circuit-construction-kit-ac_pt.jnlp

http://xviiisnefnovastecnologias.blogspot.com/2009/01/texto-de-orientao-para-oficina-de-novas.html

http://xviiisnefnovastecnologias.blogspot.com/2009/01/texto-de-orientao-para-oficina-de-novas.html

http://picintel-profjulio.blogspot.com/

http://picjrintelpucsp.blogspot.com/



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.

Documents

Determination of the electrical net frequency Lesson Plan