Basic Theoretical Physics: A Concise Overview P38. This concise treatment embraces, in four parts, all the main aspects of theoretical physics (I . Mechanics and Basic Relativity, II. Electrodynamics and Aspects of Optics, III. Non-relativistic Quantum Mechanics, IV. Thermodynamics and Statistical Physics). It summarizes the material that every graduate student, physicist working in industry, or physics teacher should master during his or her degree course. It thus serves both as an excellent revision and preparation tool, and as a convenient reference source, covering the whole of theoretical physics. It may also be successfully employed to deepen its readers’ insight and. | Some Semiquantitative Considerations on the Development of Stars 387 For free electrons with spin g-factor 2 we have kF U0 2V d3k h2k2 2n 3 2m Using d3k 4nk2dk we obtain the non-relativistic zero-point pressure Po 2U0 7 2 f kF with ef 3 V 15n2 h2k2p r 2m In the result for a classical ideal gas N r P ykBT one thus has to replace not only the thermal energy kB T by eF but also the number density N3 V by kF . essentially by the reciprocal of the third power of the separation of two electrons at the Fermi energy . In this way one again obtains the correct result apart from dimensionless constants. The zero-point pressure of an electron gas also referred to as degeneracy pressure is the phenomenon preventing the negatively charged electrons in metals from bonding directly with the positively charged atomic nuclei. This degeneracy pressure also plays an important part in the following section. Some Semiquantitative Considerations on the Development of Stars The sun is a typical main sequence star with a radius R 106 km and a surface temperature T 6000 K the mass of the sun is denoted below by M0. In contrast to the main sequence stars so-called white dwarfs . Sirius B typically have a mass M M0 of the same order as the sun but radii about two orders of magnitude smaller with R 104 km. So-called neutron stars have somewhat larger mass M M0 but R 10 km and so-called black holes which roughly put suck in all surrounding matter and radiation below a critical distance have a mass M 3 to 7 M0 or even Mq. The attractive force due to gravitation is opposed in the interior of the star by a corresponding repulsive force or internal pressure see below . Equilibrium between this internal pressure and the gravitational attraction in a spherical shell between r and r dr is found in general from the 388 53 Applications I Fermions Bosons Condensation Phenomena following identity A 2 r . M ri 2 4nr2 p r dr p r y 4nr2dr oM r . Here gM r is the mass density from
