Elements of Modern Physics — DU B.Sc. (Prog.) Physical Science courses pertaining to Electronics Previous Year Question Papers

Scheme/Mode of examinations: V - Semester Q1 Answer any five of the following: (ii) Define work function of a metal. Radiation of wavelength 5400Å falls on a metal plate with work function 1.9 eV. Find the kinetic energy of emitted photoelectrons and their stopping potential. (iii) Which law explains the continuous spectrum emitted by a Blackbody? Write its expression. Draw the energy distribution curve between wavelength (2) and energy density (Ed)) at two different temperatures. (iv) Evaluate the commutator of position and momentum operators. (v) Define mass defect and binding energy. Draw the graph between Binding energy per nucleon and atomic mass number. (vi) State Moseley's.law and write its significance. [5x3] (b) Describe gamma ray microscope thought experiment to validate Uncertainty principle. 19,6] Q3 (a) The wave function for a free particle is given by 4(x, t) = Aexpl-i/n(Et- px)], where symbols have their usual meanings. Obtain momentum (P), energy (E) and Hamiltonian (Hy operators based on this wave function and hence obtain one- dimensional time dependent Schrodinger equation. (b) What is Normalized wave function? Obtain the normalisation constant for wave function (F ofia particle confined to a box of width L. Given Ya = Alsia (nx/L) and 0 <x<L [6] Q4 (a) Explain how Sommerfield theory could overcome the limitations of Bohr's atomic theory. 17) (b) Write a relation between wavelength and Rydberg Constant (R) for hydrogen spectra and hencerfind and name the series whose wavelength lies in the visible region ofielectromagnetic spectrum. Also find the shortest and longest wavelengths of this series. 15] (c) State Bohr's correspondence principle. 13] Q5 (a) Describe in detail the construction and working principle of Van de Graaff generator using a well labelled diagram [7] (b) Obtain semi-empirical mass formula to calculate the binding energy of a nucleus. Describe all the five terms used in the formula. Useful physical constants h = 6.62 x 10 Js, Rest mass of electron, m. - 9.1 x 103 kg c = 3 x 10° m/s Rydberg's constant (R) = 1.097 x 10' m