Arcelio Hernández Fereira, Michael Thabane Magama,
Bindura University of Science Education, Zimbabwe
Abstract
Physics, Biology and Chemistry are considered the “experimental sciences”. For
that reason it is necessary to put the required emphasis in the experimental
component of the disciplines in order to develop the experimental skills and to
provide the support for the better understanding of the theoretical framework of
the physical laws. This statement is even more important in programmes
dedicated to the training of future Physics teachers. Often universities in
underdeveloped countries lack the necessary equipment for Physics Labs as a
result of funding constraints. Hence access to standard laboratory equipment is
limited due to the relative high prices demanded by the manufacturing firms. In
this case the solution lies in the development of experimental set ups using
alternative low cost materials, electronic devices, and technical solutions from
creative staff. In this work, a series of alternative set ups for University Physics
Labs and its assessment is presented. A comparison of their academic quality
and cost is made with those of standard laboratory set ups. The assessment
included such quality criteria as possibilities of satisfying the objectives of the
practice in the lab, accuracy, sensitivity and reproducibility over time. These
results are part of a wider project to address the shortage of qualified science
teachers in Zimbabwe. This alternative allows the most disadvantaged countries
to develop high quality human resources and in this way narrow the knowledge
gap between underdeveloped and developed countries.
Keywords: alternative set ups, experimental component, Physics lab
Introduction
Lab work is essential for the learner in experimental sciences because some
specific learning goals can only be achieved in this context. The goals of lab
work are available in official curricula, in laboratory instructions or from actual
practice studies. Among these goals are ‘physical manipulations of real world
substances or systems, interactions with simulations, interactions with data
drawn from the real world, access to databases, or remote access to scientific
instruments and observations’ (Committee on High School Science
Laboratories, 2006, pp. 31–32). According to this committee, lab work should
help students develop an understanding of the complexity and ambiguity of
empirical work, as well as the skills to calibrate and troubleshoot equipment
used to make observations.
The Physics labs occupy an increasingly important place in the teaching of the
courses, motivated primarily by the active character that confer to the learning
process and because they contribute to objectify knowledge, to make it more
consolidated and durable. Second, of all the forms of teaching, labs direct
students most naturally to scientific-research work, in this way, contribute to the
development of skills for research work. . Finally, performing laboratory
practical develops unique experimental skills which cannot be achieved by any
of the other (Hernández, 2001, 2002).
Recent reports from the European Commission (2007) as well as from OECD
(2006) highlights the need to change the pedagogy in science education and
emphasize the importance of a positive experience with science, especially at a
time of decline in interest in sciences and technologies.
An important aim of inquiry in the laboratory is to help students understand the
link between theory and experimental activities. This comes back to the
difficulties students often have in making the link between scientific concepts
and the experiment to be done, or later between the experimental data and the
conclusion to be drawn.
The lab work is an important part of the Physics courses. It provides the students
with a medium to practice their experimental and analytical skills and helps
them understand the basis of knowledge and the relation between theoretical and
empirical work in physics (American Association of Physics Teachers, 132 •
accessible elements 1998).
It is very important for students to understand that theory and experiment are
interlocked and cannot be separated. An observation can lead to a theory, which
may or may not stand experimental testing. Therefore, properly constructed lab
experiments become essential components of a Physics course.
It is important at this point to differentiate between qualitative demonstrations
which are normally used as teaching aids in classrooms and the more genuine
highly quantitative experiments that are typically conducted in physics labs. The
common belief is that such experiments are costly and require special support
and supervision. This also leads to the perception that low-cost home lab
experiments are inferior and cannot be considered genuine. This, in our opinion,
is a premature judgment. It is not fair at this time to compare a practice that has
been developing for more than a century with the alternative that started to
develop, in a serious manner, only about a decade ago. Isolating the physical
phenomenon from the laboratory apparatus is a first step toward finding cheaper
alternatives for observing the same physics. Therefore, we propose that with
enough research and imagination, low-cost, high-quality experiments can be
designed for the introductory physics courses.
Physics experiment is the heart of physics education. It opens the doors for
students to understand and master physical theories. It also provides students
with the essential training to use their knowledge and skills to solve scientific
problems. Lack of resources in developing countries hinders the advances in
science education especially in physics. In this paper we will shed some light on
our effort to solve this problem by building “low cost experiments”.
Quality education is the core of innovation and economic development. The 21st
century calls for well trained professionals to improve the practical capability of
the students and hence the quality of the education. Comprehensive physics
experiments can provide such capability. In underdeveloped countries, lack of
resources hinders the whole educational process. The advantage of low-cost
experiments is apparent in this situation. The benefits of hands-on experiments
that are both low-cost and high-tech are desired for both universities’
administration and students.
The hands-on experiments supply the students with the ability to actively
investigate the connection between the theoretical content of the course and its
application on real physical systems, often with the additional benefit of active
learning in a small group environment (Heller, Keith, and Anderson, 1992).
Unfortunately, many commercially existing experimental systems are complex
and too costly, thus not all institutions have the funds to supply each student
with satisfactory opportunity to experiment with such equipment. To serve this
purpose in Egypt, for example, these experiments and demonstrations have to be
affordable as much as possible. Thus a number of low-cost physics experiments
have been developed and used in some local universities and they proved to be
very successful.
The experiments fall into two categories; those qualitative experiments that
enhance the skills of observation and reflection, and those quantitative
experiments which require the collection and manipulation of data. Those
experiments can be used either in a laboratory or in a classroom as a
demonstration to engage the students more in their learning process as well as
elevate their understanding level. A special emphasis is given on easy to
assemble experiments that can fit within the budget of any physics department in
a developing country.
The lab is an essential constituent of any Physics course. Students should
understand the important relation between theory and experiment in physics.
However, the tradition has been to perform Physics experiments in especially
equipped laboratories and under the direct supervision of a lab instructor. Many
of these labs involve standard experiments and use special apparatus purchased
from certain lab equipment providers. As a result, there is a general impression
that in order to do an experiment you must go to the lab and use the special
equipment found there. We argue that this does not have to be the case. We
believe that, with good imagination and adequate research, many high-quality
physics experiments can be designed and performed safely by the students at
their homes using low-cost materials and devices.
We were able to design home lab experiments for the physics courses using
inexpensive equipment, common household items and recycled material. The
quality of the results exceeded expectations and is comparable to what is
achieved in traditional labs.
Several authors, for example, Shulman and Tamir (1973) (as cited in Hofstein &
Lunetta, 1982), Hofstein and Lunetta (1982), Bernstein (2002) have identified
the goals of laboratory instruction. They involve the development of practical
skills and knowledge and provide an opportunity to make science ‘real’. The
American Association of Physics Teachers (AAPT, 1997) has also issued a list
of goals pertaining to the introductory physics laboratory (AAPT, 1998).
According to all these authors, a good lab is one which promotes effective
learning and meets the objectives while making the laboratory experience
interesting and enjoyable. The challenge for educators is to decide which
concepts must be learned and which skills must be developed and then to design
a laboratory experience consistent with the identified objectives. We identify the
following five goals for our laboratories which are consistent with the
observations of these authors:
(1) Increase knowledge of physics
(2) Develop practical abilities
(3) Arouse and maintain interest, attitude satisfaction, and open-mindedness in
Physics
(4) Develop creative thinking and problem-solving ability
(5) Promote scientific thinking and provide practice in the experimental methods
An alternative approach is described by von Aufschnaiter and von Aufschnaiter
(2007) who state that the purpose of a laboratory is to provide structured
practical activities which promote the development of conceptual understanding,
rather than connecting pre-existing theory to practice. Rather than searching for
good experiments that demonstrates a specific concept, these researchers
promote laboratory instruction that focuses on good learning experiences, where
students can discover the concepts from their activities. Giving students the
opportunity to discover rules on their own enables them to develop an
understanding of what the scientific approach is about.
“The basis of what scientists believe and why they believe it is not the result of
mere thinking or reading in a textbook. The basis of what scientists believe is
the result of the careful collection and analysis of laboratory evidence. In any
physics class, the differentness of science will be most evident when it comes
time for lab. In the physics class, lab work is central, integral and sacred. More
than a mere place in the back of the classroom, the laboratory is the place where
physics students do physics. It is in the laboratory that physics students learn to
practice the activities of scientists - asking questions, performing procedures,
collecting data, analyzing data, answering questions, and thinking of new
questions to explore”. (The Physics classroom, 2013).
Practices in Electromagnetism courses are dominated by those dedicated to
circuits and to a lesser extent those related with measurements of magnetic field
and finally only a few associated with the electrostatic field. That is why the
traditional lab obtaining the equipotential lines of the electrostatic field in a tank
should not be abandoned because it can give a direct image and its operation is
simple. As a resource to make it more attractive we decided to combine the
experimental construction of equipotential lines with their calculation using
QuickField, specialized software, easy to use and available for free (Quickfield,
2012). By the way, we also contribute, to the development of professional skills
related with modelling, simulation and comparison of the results with
experimental measurements.
Materials and Methods
Set up for the study of the Electric Field.
Obtaining experimental equipotential lines was done in rectangular acrylic tray
dimensions 19.3 x 30.3 x 4.5 cm. In the same, water was poured and the metal
electrodes were located to generate the electrostatic field when some voltage
was applied. Three different geometries were used for the electrodes, two sharp
thin rods, two flat and two concentric circular rings. In this way, situations
corresponding to two point charges two infinite parallel flat plates and two
coaxial infinite cylinders were modelled. In this situation the obtained
equipotential lines were the result of the interception of the equipotential
surfaces of the above systems with the horizontal plane of the tray.
The electrodes were connected to the terminals of a direct current source and
applying a potential difference of 10 V. Figure 1 shows a schematic of the
installation. For the construction of the equipotential lines potentials were
measured at different points located between the electrodes and their coordinates
were recorded. The values were obtained by a digital voltmeter and the
coordinates of each point were taken from a graph paper in the transparent
bottom of the tray for the Cartesian coordinates and polar role for polar
coordinates. Excel was used to represent graphically the tabulated values of
Cartesian or polar coordinates (depending on the geometry) of the points with
the same value of potential and plotted in scatter plots and radial.
The computer calculation of the equipotential lines was done using free software
QuickField student version 5.3. This software is very easy to use by students.
Initially when drawing the geometric model plane data corresponding to the
dimensions of the tray were used and the location and dimensions of the
electrodes. Then the properties of water were introduced as a medium that fills
the tray and the values of the potential difference between the electrodes. In this
way the calculations were done to the same conditions as when experimental
measurements of the potential were made.
Figure 1. Schematic of the installation for equipotential lines electric field
Set ups for the study of the Magnetic Field:
Tangencies galvanometer. Determination of the local horizontal component of
the earth magnetic field using the interaction of magnetic dipole (a needle of a
compass) with magnetic field generated using coils with different geometries
triangle, square, rectangle, circular, etc.)
Figure 2. Schematic representation of the tangencies galvanometer
The two vectors B0 and B are perpendicular; the resulting field Bres will form
an angle  with the field B0. The simple relations are:


(1)
Changing the values of the current circulating in the coil we modify the angle 
and in the plot of B versus tan  the gradient is equal to the horizontal
component of Earth’s magnetic field. In this set up when the needle of the
compass is deviated by 45 degrees the horizontal component Earth’s magnetic
field is equal to the applied magnetic field of the used coil that can be calculated
with Biot-Savart´s law.
Another set up for magnetic field “Determination of the local horizontal
component of Earth’s magnetic field using the interaction of magnetic dipole (a
permanent magnet) with magnetic field generated with a solenoid coil” allows
us obtain the value of the horizontal component of Earth’s magnetic field and
the ratio inertia moment and magnetic dipolar moment of the permanent magnet.
The device is shown schematically in Figure 3. It consists of a solenoid coil and
a permanent magnet placed in its centre and suspended from a very long thread.
The thread exerts virtually no restoring torque to rotate through small angles.
This magnet interacts, by its magnetic dipole moment, with the resulting
magnetic field of the solenoid and the horizontal component of Earth's magnetic
field and executes harmonic oscillations, whose period is determined using a
timer.
Figure 3. Schematic of installation for the magnet-magnetic field interaction
For this assembly the following the relationship may be deduced:
 2 
m N
m

     0 i    Bext
 T 
I  L
I 
2
(2)
This shows the linear relationship between the square of the angular frequency
and the current i flowing through the solenoid coil with N turns and length L.
m
From the slope can be extracted the ratio   . Here Bext is the horizontal
I 
component of the local Earth magnetic field and can be determined from the
intercept. With the mass and dimensions of the magnet moment of inertia I may
m
be calculated and from the relationship   the magnetic dipole moment m of
I 
the magnet can be obtained. If the permanent magnet material is known and
therefore it’s mass, it is possible to estimate the magnetic moment of the atoms
under the assumption of total alignment of atomic dipoles.
Construction of a Teslameter using a Hall Effect sensor
The main characteristics of the Standard Miniature Ratiometric Linear Sensors
are:
 Small size
 Low power consumption
 Single current sinking or current sourcing linear output
 Built-in thin-film resistors - laser trimmed for precise sensitivity and
temperature compensation
 Rail-to-rail operation provides more useable signal for higher accuracy
 Responds to either positive or negative gauss
 Quad Hall sensing element for stable output
Miniature Ratiometric Linear sensors have a ratiometric output voltage, set by
the supply voltage. It varies in proportion to the strength of the magnetic field.
Figure 4 illustrates a ratiometric analog sensor that accepts a 4.5 to 10.5 V
supply. This sensor has a sensitivity (mV/Gauss) and offset (V) proportional
(ratiometric) to the supply voltage. This device has “rail-to-rail” operation. That
is, its output varies from almost zero (0.2 V typical) to almost the supply voltage
(Vs - 0.2 V typical).
Figure 4. Ratiometric linear output sensor
The transfer function of a device describes its output in terms of its input. The
transfer function can be expressed in terms of either an equation or a graph. For
analog output Hall Effect sensors, the transfer function expresses the
relationship between a magnetic field input (gauss) and a voltage output. The
transfer function for a typical analog output sensor is illustrated in Figure 5.
Figure 5. Transfer function analog output sensor.
Equation 3 is an analog approximation of the transfer function for the sensor.
Vout (Volts) = (6.25 x 10-4 x Vs)B + (0.5 x Vs)
(3)
-640 < B(Gauss) < +640
From this equation may be deduced the expression for determination of
magnetic field starting from the measurement of the output voltage (V out) and
the applied voltage from DC source (VS):
(4)
Figure 6. Physical aspect of the Standard Miniature Ratiometric Linear Hall Effect Sensors
With a 5V Dc source, a voltmeter and two Hall Effect sensors we are able to
measure the magnetic field transversal and axial. The sensors should be placed
in plastic tube and in a pad in order to build the axial and transversal probes.
Figure 7. Schema of the disposition of the Hall Effect sensor in the axial and transversal probes
The following is a relation of some possible experiments about magnetic field
that can be done using a Hall Effect sensor.
1) Magnetic field in a solenoid coil. Dependence of the intensity of the
magnetic field in a solenoid coil with its parameters (length/diameter ratio
and linear density of turns) and the position respect to the centre.
Figure 8. Magnetic field in a solenoid air coil
2) Magnetic field of a pair of coils in the Helmholtz configuration.
Dependence of the intensity of the magnetic field in a pair of Helmholtz
coils with its parameters (distance between coils respect its diameter and
linear density of turns) and the position respect to the centre.
Figure 9. Magnetic field due to a pair of coils as a function of the distance between them
3) Experimental verification of Biot-Savart’s law of a straight conductor
carrying an electrical current. Dependence of the intensity of the magnetic
field from the distance to a wire at constant current and dependence of the
intensity of the magnetic field from the current at constant distance of the
wire.
Figure10. Installation for verification of Biot-Savart’s law in a straight conductor
4) Experimental verification of Biot-Savart’s law of circular conductor loop
carrying an electrical current. Dependence of the intensity of the magnetic
field of circular conductor loops from the loop radius and the distance
from the loop and dependence of the intensity of the magnetic field from
the current at the centre of the loop.
Figure 11. Installation for verification of Biot-Savart’s law in a circular coil
Results and discussion
The appearance of the equipotential lines obtained by both methods are very
similar as shown in Figures 12-17, but the QuickField has many facilities for
students to reason with various situations that are of interest. Such a facility is to
obtain local values of the potential, the magnitude of the electric field strength
vector (or vector electric displacement) and its components.
By way of illustration the results for the case of the planar geometry electrodes
are showed. In the actual assembly the electrodes were not positioned
symmetrically about the center of the tray, nor in the horizontal position neither
the vertical one. In the results of calculations this situation is reflected in the
value of the potential shown for the center of the tray with coordinates (0,0)
which is not 5.0 V, as expected if the difference is 10V and the electrodes were
symmetrically. The value is 5.105 V, is higher because the right electrode
(connected to the positive terminal of the source) is closer to the center than the
left. Also the intensity of the electrostatic field vector E has the vertical
component (Ey) in this case down because the right electrode is slightly above
the left. If they were at the same level this component would be zero at this
point. Another possibility is to highlight the relationship between the direction
of the lines of force of the electric field intensity vector and the equipotential
lines (see Figures 18-20).
In discussing the results obtained from the calculations using the QuickField we
have the possibility to display also the lines of force of the electric field intensity
vector and students can check the condition that these are perpendicular to the
equipotential lines.
Figure 12. Aspect of equipotential lines for plane electrodes and local values for a point in the middle
of the
electrodes.
Electrodos planos
8
Y, cm
6
4
2V
3V
2
4V
5V
6V
7V-12
8V
9V
0
-10
-8
-6
-4
-2
0
2
4
6
8
10 X, cm
12
-2
-4
-6
-8
Figure 13. Aspect of equipotential lines for plane electrodes drawn from experimental values
Figure1 4. Aspect of equipotential lines for point electrodes and local values for a point in the middle of
the electrodes
Cargas Puntos
6
Y, cm
4
2
Potencial 5V
Potencial 4,5V
Potencial 6V
Potencial 7V
Potencial 3V
Potencial 2,5V
X, cm
0
-20
-15
-10
-5
0
5
10
15
20
-2
-4
-6
Figure 15. Aspect of equipotential lines for point electrodes drawn from experimental values
Figure 16. Aspect of equipotential lines for circular electrodes and local values for a point in the
middle of the
electrodes
Electrodos circulares
15
360
345
7
30
45
6
330
60
5
4
315
75
3
2
300
3V
5V
7V
9V
90
1
285
0
105
270
120
255
135
240
150
225
165
210
180
195
Figure 17. Aspect of equipotential lines for circular electrodes drawn from experimental values
Figure 18. Lines of force of the electric field intensity vector for point electrodes and local values for a
point in the middle of the electrodes
Figure 19. Lines of force of the electric field intensity vector for circular electrodes and local values
for a point in the middle of the electrodes
Figure 20. Lines of force of the electric field intensity vector for plane electrodes and local values for a
point in the middle of the electrodes.
From the tangencies galvanometer may be obtained the angles of the position of
the needle of the compass for different magnetic fields and do a plot like the
following showed in figure 21.
Figure 21. Plot of Magnetic field versus angular position of the needle of the compass
The local values of Earth´s magnetic field and its components can be accurately
determined using free software on line or downloaded from special sites. These
programs use the latitude, longitude and elevation of the location as input
variables. The National Geophysical Data Centre offers two software WMM
2010 and IGRF 11. The calculations for Harare are shown in the table 1.
Table 1 . Calculation of Earth´s magnetic field in Harare using the WMM 2010 model.
Magnetic Model: WMM2010
Latitude: -17.820 degrees
Date in
YY-MM-DD
format
Longitude: 31.020 degrees
Place: Harare
Elevation: 1200 meters
2011/12/10
Declination
in decimal
degrees
-8.219
Inclination in
decimal
degrees
-55.821
Horizontal
Intensity
in nT
17216.9
East
Component
in nT
-2461.3
North
Component
in nT
17040
Vertical
Component
in nT
-25354.2
Total
Field
in nT
30647.3
2012/12/10
-8.212
-55.78
17233.4
-2461.6
17056.7
-25338.9
30643.9
Change per year
0.007
0.042
16.5
-0.3
16.6
15.3
-3.4
Figure 19 shows the dependence of the magnitudes involved in equation (2). As
can be seen exhibiting behaviour is linear with correlation coefficient R2 =
0.9996 and experimentally confirmed the correctness of this equation.
Figure19. Plot of magnitudes involved in the equation (2)
Taking the value of the slope and the intercept with the vertical axis provided by
the fitted equation the value of the horizontal component of the local earth
magnetic field was found which resulted equal to 26 T. The comparison with
the values of the calculations by IRGF11 model is satisfactory (see table 2).
Table 2 . Calculation of Earth´s magnetic field at Cienfuegos using the
IGRF11 model.Magnetic Model: IRGF11
Latitude: 22.140 degrees
Date in
YY-MM-DD
format
2011/12/10
Longitude: -80.440 degrees
Place: Cienfuegos
Elevation: 0 meters
Declination
in decimal
degrees
-5.327
Inclination in
decimal
degrees
51.682
Horizontal
Intensity
in nT
26177.3
East
Component
in nT
-2430.2
North
Component
in nT
26064.2
Vertical
Component
in nT
33124.8
Total
Field
in nT
42219.7
2012/12/10
-5.433
51.57
26163.1
-2477
26045.6
32974.2
42092.8
Change per year
-0.106
-0.113
-14
-46.8
-18.6
-150.6
-126.6
Conclusions
1) The experimental component of Physics courses, offered to science
teachers students, is transcendental during their training and for the future
professional activity in classrooms.
2) With enough research and imagination, low-cost,
experiments can be designed for the Physics courses.
high-quality
3) For universities of the underdeveloped countries many commercially
existing experimental systems are complex and too costly, thus the lowcost physics experiments have been developed with the same academic
features and they proved to be very successful.
4) To develop a quality experimental component during the training of the
future Physics teachers could contribute to improve the quality of the
students incoming to universities and specially to increase the number of
those that decide to study Science careers.
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