Students' Understanding of Direct Current Resistive Electrical Circuits

Research has shown that both high school and university students' reasoning patterns regarding direct current resistive electric circuits often differ from the currently accepted explanations. At present, there are no standard diagnostic examinations in electric circuits. Two versions of a diagnostic instrument called Determining and Interpreting Resistive Electric circuits Concepts Tests (DIRECT) were developed, each consisting of 29 questions. The information provided by the exam provides classroom instructors a means with which to evaluate the progress and conceptual difficulties of their students and their instructional methods. It can be used to evaluate curricular packages and/or other supplemental materials for their effectiveness in overcoming students' conceptual difficulties. The analyses indicate that students, especially females, tend to hold multiple misconceptions, even after instruction. During interviews, the idea that the battery is a constant source of current was used most often in answering the questions. Students tended to focus on current in solving the problems and to confuse terms, often assigning the properties of current to voltage and/or resistance. Results indicated that students do not have a clear understanding of the underlying mechanisms of electric circuit phenomena. On the other hand, students were able to translate easily from a "realistic" representation of a circuit to the corresponding schematic diagram.Comment: This article has been accepted for publication in the American Journal of Physics - Physics Education Research Supplement. No known publication date as ye

Electrode boundary layers in direct-current plasma accelerators

One of the problems that must be faced in the development of direct-current plasma accelerators is that of boundary-layer growth on the electrode surfaces. These surfaces must be maintained at a somewhat lower temperature than is desirable in the bulk of the gas flow. The associated reduction in electrical conductivity near the electrode surface, together with the continuous current through the boundary layer, may result in greatly augmented Joule heating near the surface, and increased heat transfer. This phenomenon is treated within the framework of boundary layer theory. It is found that similar solutions for the thermal and viscous boundary layers exist for a certain class of accelerated flows in which the velocity varies as a power of the streamwise coordinate. The solutions show that the heat-transfer rate at Mach numbers near unity may be as much as ten times that which would be expected for a normal boundary layer. At higher Mach numbers, the similarity is not precisely valid; however, the analysis indicates qualitatively that a stagnation enthalpy overshoot may occur in the high-temperature portion of the boundary layer as a result of the electromagnetic acceleration

Signal generator converts direct current to multiphase supplies

Multiphase wave generator uses multivibrators in a feedback control mode that produces output signal pairs that are impressed on the primary windings of inverter transformers sequentially with a 120 degree phase shift from each other

Kohn-Sham equations for nanowires with direct current

The paper describes the derivation of the Kohn-Sham equations for a nanowire with direct current. A value of the electron current enters the problem as an input via a subsidiary condition imposed by pointwise Lagrange multiplier. Using the constrained minimization of the Hohenberg-Kohn energy functional, we derive a set of self-consistent equations for current carrying orbitals of the molecular wire

On the calibration of direct-current current transformers

Modern commercial direct-current current transformers (DCCT) can measure currents up to the kA range with accuracies better than 1E-5. We discuss here a DCCT calibration method and its implementation with commercial instruments typically employed in low resistance calibration laboratories. The primary current ranges up to 2 kA; in the current range below \SI{100}{\ampere} the calibration uncertainty is better than 3E-7. An example of calibration of a high-performance DCCT specified for primary currents measurement up to 900 A is discussed in detail.Comment: Accepted for publication in IEEE Trans. Instr. Meas. Copyright IEE

Magnetometer and direct-current resistivity studies in Alaska

During the past year and a half, the territorial Department of Mines in Alaska has conducted a modest experimental program for the purpose of determining the extent to which magnetic and resistivity methods can be used in interior Alaska in connection with prospecting, mining and geological studies. Since little information is available concerning previous work, and since conditions differ considerably from those in most other regions, it was considered advisable to make a general study of the possibilities and limitation[s] of the two methods, rather than a detailed study of any single problem.Foreword -- Problems -- Instruments and methods -- Location of buried placers -- Thawed and permanently frozen overburden -- Underground water -- Conclusions -- References