295 research outputs found
Four errors students make with inverse-square law vectors
In this paper, we discuss four errors introductory physics students make when
attempting to add two inverse-square law vectors. We observe multiple instances
in which students 1) add vectors as if they were scalars, 2) project the
(or ) in the denominator, instead of the entire vector, when attempting to
find the vector's components, 3) incorrectly apply the Pythagorean theorem when
attempting to calculate the magnitude of the resultant vector, and 4)
incorrectly relate the signs of the components of an electric field (or force)
to the signs of the electric charges. While these are not the only errors
students make, they are the most frequently occurring based on our analysis of
678 exams taken by students in either introductory mechanics or electricity and
magnetism (E&M). We then show how these errors can be encoded into a new type
of activity or assessment question which we call a ``student error task."
Introductory physics instructors can use the student error task in this paper
as a way to engage or assess their students' understandings of how to add two
inverse-square law vectors.Comment: 22 pages, 7 figures, submitted to the European Journal of Physic
Entropy creation inside black holes points to observer complementarity
Heating processes inside large black holes can produce tremendous amounts of
entropy. Locality requires that this entropy adds on space-like surfaces, but
the resulting entropy (10^10 times the Bekenstein-Hawking entropy in an example
presented in the companion paper) exceeds the maximum entropy that can be
accommodated by the black hole's degrees of freedom. Observer complementarity,
which proposes a proliferation of non-local identifications inside the black
hole, allows the entropy to be accommodated as long as individual observers
inside the black hole see less than the Bekenstein-Hawking entropy. In the
specific model considered with huge entropy production, we show that individual
observers do see less than the Bekenstein-Hawking entropy, offering strong
support for observer complementarity.Comment: 13 pages. This is a companion paper to arXiv:0801.4415; Added
reference
Clebsch-Gordan Construction of Lattice Interpolating Fields for Excited Baryons
Large sets of baryon interpolating field operators are developed for use in
lattice QCD studies of baryons with zero momentum. Operators are classified
according to the double-valued irreducible representations of the octahedral
group. At first, three-quark smeared, local operators are constructed for each
isospin and strangeness and they are classified according to their symmetry
with respect to exchange of Dirac indices. Nonlocal baryon operators are
formulated in a second step as direct products of the spinor structures of
smeared, local operators together with gauge-covariant lattice displacements of
one or more of the smeared quark fields. Linear combinations of direct products
of spinorial and spatial irreducible representations are then formed with
appropriate Clebsch-Gordan coefficients of the octahedral group. The
construction attempts to maintain maximal overlap with the continuum SU(2)
group in order to provide a physically interpretable basis. Nonlocal operators
provide direct couplings to states that have nonzero orbital angular momentum.Comment: This manuscript provides an anlytical construction of operators and
is related to hep-lat/0506029, which provides a computational construction.
This e-print version contains a full set of Clebsch-Gordan coefficients for
the octahedral grou
Using graphical and pictorial representations to teach introductory astronomy students about the detection of extrasolar planets via gravitational microlensing
The detection and study of extrasolar planets is an exciting and thriving
field in modern astrophysics, and an increasingly popular topic in introductory
astronomy courses. One detection method relies on searching for stars whose
light has been gravitationally microlensed by an extrasolar planet. In order to
facilitate instructors' abilities to bring this interesting mix of general
relativity and extrasolar planet detection into the introductory astronomy
classroom, we have developed a new Lecture-Tutorial, "Detecting Exoplanets with
Gravitational Microlensing." In this paper, we describe how this new
Lecture-Tutorial's representations of astrophysical phenomena, which we
selected and created based on theoretically motivated considerations of their
pedagogical affordances, are used to help introductory astronomy students
develop more expert-like reasoning abilities.Comment: 10 pages, 10 figures, accepted for publication in the American
Journal of Physic
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