Brooke Reed
Physic’s lab formal lab
March 18, 2015
1.) Does the abstract meet Dr. Selkowitz's criteria?
Dr. Selkowtiz’s criteria for abstract are that it provides an overview of the
experiments and concludes the results of the experiment. The point of the
abstract is to inform the reader of what is the topic of the paper and their
findings in a clear and condensed manor. The abstract in the paper Analysis
of Surstylus and Aculeus Shape and Size Using Geometric
Morphometrics to Discriminate Rhagoletis pomonella and Rhagoletis
zephyria does follow Dr. Selkowitz’s criteria except for the format regarding
font size (the criteria includes that the font is smaller for the abstract). The
paper highlights the problem of not being able to distinguish Rhagoletis
pomonella and Rhagoletis zephria when assessing apple orchard for
pesticide requirements. The abstract also includes what the experimenters
did; in this case they assess the difference of surstyli shape between the two
species. From there they were able to preform an assessment test to test
whether using the measurements of the surstyli was a successful way to
distinguish the species. The conclusion of these results were also including in
the abstract.
2.) What was the hypothesis of the paper?
The hypothesis of the paper was to analyze the difference in surstylus shape
to determine if surstyli can be useful for correct species identification
between the R. pomonella and R. zephryia.
3.) How was the data in the paper collected?
The two types of fruit used in the research was infested hawthorn and
snowberries harvested from Washington or Oregon in 2007-2008; the large
majority of the fruit was collected from the ground. The fruit was then
analyzed further in either Washington State University located in Vancouver,
WA or USDA-ARS laboratory in Wapato, WA. The puparia was collected from
the fruit samples and stored at 3-4 degrees celsius in moist soil. After the
puparia develop into adults (~6 months of incubation) they were frozen or
allowed to die in cages. After death the flies were stored in 70%ethanol.
4.) What was the main statistical test used to address the hypothesis? What plot
or graph showed this result clearly?
Table 5. Jacknifed grouping using aculeus shape and size from CVA- distance
based method for assigning specimens to groups. This Table shows a strong
differentiation in surstylus shapes between the species as well as little
differentiation within the species. These results were highlighted in figure 4.
Figure 4 represents a scatter plot of the CVA of surstylus shapes comparing
the two species and the groups within the species (six groups of R. pomonella
and two groups of R. zephyria). While figure 2 and 3 include photographical
differences between the species, figure 4 includes a more in depth analysis of
the differences between the species and the similarities within the species.
The hypothesis studies whether the surtylus can be used to identify the
species and figure 4 provides the best representation of the surtylus
difference between two species and of little separation within the species
supporting the hypothesis.
5.) Do you believe the hypothesis was proved or not?
Yes, the hypothesis was proved therefore surstylus shape could be used as a
practical method to distinguish between the two species. The results,
particularly those represented in figure 4, includes the p value of <. 0001,
indicating that the results were statistically significant. “The CVA axes plot of
the two groups (all R. pomonella versus all R. zephyria showed a strong
separation”, in addition “A MANOVA of surstylus shape of flies categorized in
eight (six R. pomonella and two R. zephyria) or in two groups (all R.
pomonella versus all R. zephyria) was significant (Table 2). However, a CVA
using all six R. pomonella groups (data not shown) was not significant (P <
0.05), and a CVA using the two R. zephyria groups (data not shown) was not
significant (P > 0.05), so we could not distinguish populations within
species.” This demonstrates that there is a difference between the two
species, and that the difference within each species is not significant.
6.) All writing, even scientific writing, needs to tell a story to be interesting. In
one paragraph, what was the story in the apple maggot paper? Why would
anyone care about it?
Do to morphological similarities it is difficult to distinguish between R.
pomonella (which food source include commercial apples) and R. zephryia
(which food source, snowberry, and is not a menace). Due to their
similarities, pest control on orchards becomes difficult and crops may
undergo unnecessary pesticides spray to control R. pomonella populations.
By analyzing surstylus shapes along with aculeus shapes a method less costly
then current genitalic morphology tests could be developed saving time and
reducing costs in the apple industry. The results of the findings concluded
that surstylus can be used to correctly identify the species; while aculues
shapes did distinguish between the two, this distinguish was not as prevalent
as in the males but still proved to be advantageous.
Use of Voltage to Measure Electric Field Strength
Brooke Reed
Jenny Wachala, Laura Owczarzak, Rachel Singer
Department of Physics, Canisius College
Abstract:
Electric fields are created when an object is charged, this object is known as
the source charge. When this source interacts with its surrounding a electric
field is formed, this field has both magnitude and direction making it a vector
quantity. To illustrate the field, measurements of the voltage at specific
locations surrounding the source charge are reported and then transferred to
a map, outlining the field strength. To overcome the difficulty of measuring
the electric field directly, due to its vector qualities, the voltage of the field
was measured. These measurements were transferred to graph paper
mirroring the field. As a comparison a EMField computer simulator was used
produce the electric fields under the same source charge scenarios analyzed
in lab.
Introduction and theory:
Electric fields are formed when a charged object interacts with the space
around it. This non-contact force is complicated to illustrate, however there
many parallels between electric field strength and potential energy or
gravitational energy that help to demonstrate this phenomenon.
Topographic maps shows changes in elevation or potential energy of the
earth’s surface. Closer field lines indicate a steep change in energy or slope;
field lines that are father apart indicate a gradual slope because there is more
distance between the changing field lines. “Tightly spaced lines on a topo
map indicate a steep slope, so closely spaced voltage lines indicate a steep
slope and strong electric field line” (Reed 2015). The lines specify a
particular potential energy; this energy is held constant across the line for
equal height lines are equal energy lines. Therefore motion along a line
would not produce a change in electric potential. Similarly equipotential lines
indicate constant potential across a line. The electric fields lines also provide
magnitude and direction of the field, where the lines are closer the
magnitude is the highest and this direction decreases from high to low as you
go perpendicular to the lines.
The electric field produced by a charged object creates electric forces; this is
equal to electrical energy. Voltage describes the relationship of electrical
energy and charge, therefore voltage is used to measure the potential energy
of the field created by a source charge as illustrated in equation 1.
𝑉𝑜𝑙𝑡𝑎𝑔𝑒 (𝛍𝒆 ) =
𝑒𝑙𝑒𝑐𝑡𝑖𝑟𝑐𝑎𝑙 𝑒𝑛𝑒𝑟𝑔𝑦 (𝛍)
𝐶ℎ𝑎𝑟𝑔𝑒 (𝑞)
(1)
The electric field energy travels from a high energy to a low energy, as the
distance between the source charge increases the energy will decrease. This
is represented in equation 2.
𝑞
1 𝑞
=
𝑟 4𝜋ℰ0 𝑟
𝑉=𝐾
(2)
Using this formula we predicted that if there is only one source (q), the result
will be a uniform field and equal distances (r) from the source will result in
equal potential energies. Similarly the electric potential outside a charged
sphere is the same as that of a point charge. The electric potential of a
charged sphere can be calculated using equation 3.
𝑉=𝐾
𝑄
1 𝑄
=
𝑟 4𝜋ℰ0 𝑟
(3)
In equation 3, the (r) representative the radius of the sphere and (Q) is
representative of charge. In both equations 2 and 3 there is an inverse
relationship between the electric potential (V) and distance or radius (r).
Multiple sources will lead to either attractive or repulsion forces in the field
and the equal potential lines will be analogs to the electric field shape. When
there are two source charges the following equation can be used to calculate
the electric potential.
𝑈𝑒𝑙𝑒𝑐 = 𝐾
𝑞𝑞′
1 𝑞𝑞′
=
𝑟
4𝜋ℰ0 𝑟
(4)
The electric potential equation (4) can be used to calculate both positive and
negative charges. Equation (4) is equally valid for opposite charges and the
electric potential as a result is negative indicating that the potential energy of
the two charges decreases as the distance between them decreases.
Procedure:
Three carbon sheets with electrodes on them where analogous to three
source charge scenarios (one with a single source charge, one with two
parallel line of different voltages and one between two separate charges). To
map out the equal voltage surfaces graph paper representing the field was
used as a template. Voltage readings of the carbon sheet were measured and
transferred to the same location on the template. Equal voltages were
connected, creating the equal potential energy lines. Using equation (4), the
direction of the field was found since the voltages either increased of
decreased from the source charges. The direction was indicated on the
template using an arrow symbol. An EMField simulator was used to compare the
results of the carbon sheet study and a computer-simulated scenario.
Data and analysis:
To better understand electric fields, three different scenarios and their
electric fields were analyzed. The first scenario was a small, heavy, circular
asteroid in space. The resulting energy surfaces are diagramed in figure 1.
Figure 1
Figure 1. The black circle in the circle represents the asteroid. The surrounding lines
indicate the equal energy surfaces and the arrow is in the direction of gravity.
The field strength becomes weaker as the distance from the asteroid increases. The
asteroid is also the center of gravity.
The next scenario analysis the equal energy lines on earth over a flat landscape such
as the desert. The resulting energy surfaces are diagrammed in figure 2.
Figure 2
Figure 2. The equal potential lines are located above the earth’s surface, the arrows
Earth’s surface
indicating the direction of gravity.
The field strength in figure 2 decreases as the distance from earth increases; the
direction of gravity is towards the earth’s surface.
The last scenario denotes two stars in parallel with each other. The equal potential
lines are diagrammed in figure 3.
Figure 3
Figure 3. The stars are in parallel with each other and the lines in between them represent
equal potential. The arrows indicate the direction of gravity.
The stars depicted in figure 3 have equal potential lines that increase as the distance
between each star decreases. The area directly in between the stars experience equal but
opposite forces therefore the potential energy is zero.
The impact of charges was explored for each of the pervious scenarios. The direction
of gravity was analogous to the location of the negative charge. The positive charge was
located in the surround field of the negative. The charge shows the direction of the field, the
center of the field is negative and the positive charge is directed towards it, this is similar to
the direction of gravity as depicted in figures 1-3. The field is altered based whether the
charges are positive or negative, for opposite charges attract and objects with the same
charge (positive-positive or negative-negative) will repel. If the center of the field was
positive and the outer field charges were negative the direction of the charge would reverse.
To compare these to the charges applied in lab an EMField simulator was used to simulate
the models and compare to the charge scenarios. The simulator reflected the previous
results, indicating that the direction of the forces were in accordance with our prediction.
The carbon sheets were analysis and the templates produced are represented in figures 4
and 5.
Figure 4
Figure 4: The template produced in lab of the single source charge scenario
The template of a single source charge scenario is analogous to that found in figure one and
the EMField simulator. The source charge voltage at the center is 14.5V, this value decreases
to 6V, 4.5V, 2V, and 1V as the readings are taken further away from the source charge.
Arrows show the direction of energy as potential energy decreases from a high energy to a
low energy in the field.
Figure 5
Figure 5: The template produced in lab of the desert scenario of two parallel equal
potential source charges.
The template of two source charges in a parallel lines depicted in figure 5 were analogous to
those analyzed in the desert scenario and the EMField simulator. Furthermore, the equal
potential lines decrease from 9V to 0V, indicating the directionally of the field from right to
left. The curves of the equal potential lines are a result of fringing.
The last scenario could not be measured in lab due to faulty carbon sheets that were unable
to provide accurate voltage readings. We would have expected the results to be similar to
those found in figure 3.
Conclusion:
The use of voltage provides an accurate representation of potential energy of a field
surrounding a single source charge or several. The equal potential voltages give rise to
equal energy field lines, when connected these lines are helpful in visualizing energy
changes due to the presence of a charge. Further analysis of their voltages and distances
from the source charge can be graphed to test whether the equations 1-3 produce an
inverse relationship of voltage and distance from the charge.
Work Cited:
Reed, Brooke. “PHY 202: Electric Field Mapping.” Experiment of General Physics Lab
(2015). 1-2.
Knight, Randall Dewey., Brian Jones, and Stuart Field. College Physics: A Strategic
Approach. San Francisco: Pearson/Addison Wesley, 2007. Print.