Abstract. The derivation of the efficiency of Carnot cycle is usually done by calculating the heats involved in two isothermal processes and making use of the associated adiabatic relation for a given working substance's equation of state, usually the ideal gas. We present a derivation of Carnot efficiency using the same procedure with Redlich-Kwong gas as working substance to answer the calculation difficulties raised by Agrawal and Menon [1]. We also show that using the same procedure, the Carnot efficiency may be derived regardless of the functional form of the gas equation of state.

We consider the problem of designing an Ansatz for the fermion-photon vertex function, using threedimensional quantum electrodynamics as a test case. In many existing studies, restrictions have been placed on the form of the vertex Ansatz by making the unsubstantiated assumption that in the quenched, massless limit the Landau gauge Dyson-Schwinger equations admit a trivial solution. We demonstrate, without recourse to this assumption, the existence of a nonlocal gauge in which the fermion propagator is the bare propagator. This result is used to provide a viable Ansatz for part of the vertex function. ͓S0556-2821͑98͒00220-3͔

We investigate the destroying of charged and rotating black holes in Einstein-Maxwell-(dilaton) theory. We show that a test particle with some appropriate properties in the black hole background can turn the black hole into a naked singularity. In this work, we neglect the self-force, self-energy, and radiative effects as considered by some others in literature. As the result, we are able to show that the Kerr-Newman and Kaluza-Klein black holes can be destroyed by the test particle. Furthermore, for Kaluza-Klein black hole, we consider the overspinning of the black hole by a neutral test scalar field.

A short comment regarding the derivation of Lorentz transformation proposed by Iyer and Prabhu (2007 Eur. J. Phys. 11 183–90) is given. It is shown that the proposed derivation is similar to that appearing in the standard textbooks of classical mechanics, electrodynamics and the theory of relativity. In fact, those textbooks also provide an elegant form of the Lorentz matrix for the (3+1)-dimensional case, which Iyer and Prabhu claim to be difficult to attain because of its algebraic complexity. We also provide the derivation of the (3+1)-dimensional version of the Lorentz matrix using a method analogous to that proposed by Iyer and Prabhu, and show that the result is completely equivalent to the (3+1)-dimensional version appearing in the textbooks.

Abstract-Electromagnetic concepts are abstract, difficult and complex concepts. There are different conceptions understood by students in learning electromagnetic concept. This study aims to identify and describe the conception of high school students who have been studying electromagnetic. Descriptive method used in this research. The subjects consist of 27 respondents of 12th grade students. The data collection done by providing an essay test instruments referred to test models of Electromagnetism Concept Inventory (EMCI) those includes subconcepts of Electrostatic, Magnetism, Electromagnetic induction and Electromagnetic waves. The result of data analysis shows that only 2% of respondents answered correctly on the subconcepts of magnetism. In other sub-concepts there were no respondents who answered correctly. Moreover, the conceptions understood by respondents about electromagnetic concept were very diverse.