Optionals IAS Mains Physics: Questions 139 - 144 of 307

In semiconductor physics, the band gap of a semiconductor is of two types, a direct band gap and an indirect band gap. The minimal – energy state in the conduction band and the maximal – energy state in the valence band are each characterized by a certain crystal momentum vector in the Brillouin zone. If the vectors are the same, it is called a …

For , the radius of the zone, the relation can be written as

is the distance of the source from the zone plate and is the distance of screen from the plate. Since (given) , the relation becomes

• Density of states, is the total number of available electronic states (or orbitals) per unit energy range at energy . To obtain the expression for , we consider the linear momentum which, in quantum mechanics, is represented by the operator

• This equation represents a standing wave solution. it is however more convenient to work with the plane trav…

• Van Laue treated the phenomenon of diffraction in a more general way by considering the scattering of X – rays from individual atoms in the crystal followed by their recombination to obtain in the direction of the diffraction maxima. It will be shown below that diffraction maxima appear in some specific directions which obey certain conditions know…

• Transistor consists of a silicon or germanium (preferably silicon because of its smaller cut off current , smaller variations in due to variations in temperature and higher operating temperature) crystal in which a layer of type material is sandwiched between two layers of type material, as shown in fig (1a) . Alternatively, a transistor may con…

.

Time as measured by stationary observer

Time measured by moving object

Time measured by the observer on the earth will be whereas the lifetime of the particle in its own frame of reference was .