Pontifícia Universidade Católica de São Paulo
Junior Scientific initiation at PUC/SP and the development of experimental activities in Physics
using the Classmate PC
MAGNET’S FALL THROUGH REELS
Lesson Plan
Prof.Rossana Leandro
Students from the 11th grade –E.E José Chaluppe
Bianca de Souza
Jhéssica Carvalho
Yasmyn Shantala
Supervision: Prof. Marisa Almeida Cavalcante(PUC/SP) and Cristiane
R.C.Tavolaro (PUC/SP)
August 2009
Pontifícia Universidade Católica de São Paulo
Junior Scientific initiation at PUC/SP and the development of experimental activities in Physics
using the Classmate PC
Objectives
Study the magnetic induction. Examine the behavior of an induced current in a reel during
the movement of the magnet in its interior.
To understand the characteristics of accelerated motion.
Measure the acceleration’s value of a falling body.
Determine graphically and analytically the acceleration of a falling magnet in reels.
Content
The content approached in this activity allows us to treat the following structuring themes
of the 12th grade:
Fields and electromagnetic forces. Electromagnetic induction.
The study of electromagnetism.
Fall of bodies under gravitational action and in the presence of magnetic friction.
Kinematics characteristics of a body in accelerated motion: variation of its position over
time and graph, variation of its speed over time and graph.
Competences and abilities
Representation and communication
• Use and understand tables, graphs and graphic mathematical relationships to express
physics knowledge.
• Express oneself correctly using the appropriate physics language and elements of its
symbolic representation.
Investigation and understanding
• To know and use physics concepts. Relate magnitudes, quantify and identify relevant
parameters. Understand and use physics laws and theories.
• Build and investigate problems, identify the physics situation, use physics models,
generalize from another situation, foresee, evaluate, and analyze prediction.
Socio-cultural and historical perception
• To relate through written language experiments and questions relative to the identification
of the relationship between magnetic field and electrical field; identify electromagnetic
phenomena, establish relationships and identify regularities; use procedures and
observation instruments, represent experimental results, elaborate hypotheses and
interpret results in situations that involve electromagnetic phenomena.
Material
PC Classmate Intel
Pontifícia Universidade Católica de São Paulo
Junior Scientific initiation at PUC/SP and the development of experimental activities in Physics
using the Classmate PC
1 magnet (from earth is preferred)
Ruler
A plastic tube with 4 surbases (10 cm apart approximately)
Connectors wires for the reels (with pins banana-banana)
Enameled copper wires no. 26 (90 cm of wire for each surbase)
Audacity (free software for sound edition and analysis)
Wires with banana pins and a plug connector for the microphone entrance of the sound board of
the classmate PC.
Activity
Amount of classes necessary for the activity: 4 classes
First class
Study of Faraday's Law - Theoretical Introduction
When the magnetic flow through the surface of a surbase varies, an induced electric
current appears in the surbase. In the presence of an induced electric current in the circuit we
conclude that there should be an induced electromotive force that produces it. Experimentally
Faraday observed that the faster the variation of the magnetic flow, the larger is the induced
eletromotive force. It is possible to show using the simulator INTERACTIVE SIMULATIONS
UNIVERSITY OF COLORADO.
(http://phet.colorado.edu/simulations/sims.php?sim=Faradays_Electromagnetic_Lab)
Click on "electromagnetism laboratory". Verify what happens to the circuit when the magnet gets
closer or away from the reel.
Second class
To assemble the equipment and give details about its operation.
The reels can be built on their own tube, with a single wire, so that they will be connected in
series. The terminals of that wire should be connected to the microphone entrance of the sound
board of the classmate PC through a plug in connector. The magnet will be abandoned on the top
of the tube and the signal will be observed in the software Audacity of sound analysis.
Pontifícia Universidade Católica de São Paulo
Junior Scientific initiation at PUC/SP and the development of experimental activities in Physics
using the Classmate PC
Illustration 1: Assembly of the solenoid with two surbases connected to the Classmate PC.
Illustration 2: To the left, detail of the connection of the wires with the reel and to the right, detail of the position of
where to leave the magnet so that it falls passing through the reels.
Pontifícia Universidade Católica de São Paulo
Junior Scientific initiation at PUC/SP and the development of experimental activities in Physics
using the Classmate PC
Illustration 3: Fall of the small Magnet. (Plastic Tube)
Illustration 4: Solenoid connected to the Classmate.
Illustration 5: Terminals of the reels with the connectors.
Pontifícia Universidade Católica de São Paulo
Junior Scientific initiation at PUC/SP and the development of experimental activities in Physics
using the Classmate PC
Illustration 6: Screen of the Audacity software showing the variation of the induced electromotive force in the reel
during the time of fall of the magnet.
Third class
The collection and data processing will be done through the microphone entrance in the
Classmate PC. We began the experiment connecting the reels in series and the connector wire to
the microphone entrance of the Classmate PC. We pressed the key "record" in the Audacity
software and we left the magnet on the extremity of the tube. The software will register the
variation of the electromotive force every time the magnet passes through a reel.
Fourth class
Analyze the fall of the magnet. To get to the result of the motion we need to measure the
distances between two consecutive reels (distance that can be chosen before the experiment,
during the assembly of the reels), and of the time interval of the passage of the magnet between
the two reels. To measure the time, we just need to select with the mouse the time interval of the
electromotive force variation in the Audacity software.
Make a two column data table, one for displacement and the other for time passed.
Table 1: Displacement over time
t
0
0.05
0.1
0.13
s (cm)
0
9,7
19,4
28,5
Pontifícia Universidade Católica de São Paulo
Junior Scientific initiation at PUC/SP and the development of experimental activities in Physics
using the Classmate PC
0.17
0.20
0.22
0.25
38,6
47.8
57
67
The magnet's fall depends on the local acceleration of gravity, that is, it executes an accelerated
motion and its function is
s=s0+v0t+1/2.at2,
2
Where s0=0 e v0=0 (s=1/2.at ).
We want to determine a, the acceleration of the fall. For that, we made a s x t graph, where y
2
equals to s and x equals to t. This way, the coefficient that accompanies the term x is 1/2.a.
Results Analysis
Determine the acceleration of the fall starting from the function obtained.
In the example above we obtained:
a= 493,79 x 2 = 987cm/s2
a = 9,87 m/s2
The obtained result is below the acceleration of the gravity (g=9,78 m/s2). Despite the apparent
free fall of the magnet inside the tube, we cannot forget about the magnetic friction exerted by
the electromagnetic induction force created by the reels. Therefore the result is coherent with the
preliminary study carried out about electromagnetic induction.
Pontifícia Universidade Católica de São Paulo
Junior Scientific initiation at 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://www.pic.pucprofrossana.blogspot.com/ (accessed on 17/08/2009)
Audacity Software http://audacity.sourceforge.net/download/ (accessed on 17/08/2009)
Text about analogical – digital signal conversion
http://xviiisnefnovastecnologias.blogspot.com/2009/01/texto-de-orientao-para-oficina-denovas.html
Magnet’s fall through the reel simulator (accessed on 17/08/2009)
http://phet.colorado.edu/simulations/sims.php?sim=Faradays_Electromagnetic_Lab
http://profvalmir.blogspot.com/2009/09/roteiro-do-experiemento-do-tubo-pvc-e.html
Reference
Cavalcante, Marisa Almeida; TAVOLARO,Cristiane .R.C.;BONIZZIA,Amanda ; e PIFER,Anderson.
“Novas Tecnologias no Ensino de Física” GOPEF/PUC-SP 2008.
http://xviiisnefnovastecnologias.blogspot.com/2009/01/texto-de-orientao-para-oficina-denovas.html