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FPSC · CSS 2023

Physics, Paper II

100 marks · 3 hours · 6 questions · official PDF, 1 page
This paper Physics · all yearsQ. 3 · Consider a pair of copper…Q. 4 · Give expressions for the following…Q. 5 · An atom is capable of…Q. 6 · Consider the elastic vibrations of…Q. 7 · Discuss density of states in…Q. 8 · Write Notes on any TWO…With this paperOfficial PDF1 pp← 20232024 →
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Part II

Q. 3
  1. (a)Consider a pair of copper wires 1 mm in diameter and 5 cm apart. In copper the number of conduction electrons per cubic meter is 8.45 x10 28 . Suppose their mean drift velocity v is 0.3 cm / s, calculate current in each wire. [8]
  2. (b)If the wires are 20 cm apart, calculate the magnetic force on the wires. [8]
  3. (c)Define electric current in a wire with respect to number of charges and their drift velocity. [4]
(20)
Q. 4

Give expressions for the following quantities in terms of e, h, c, k, m e and m p .

  1. (a)The energy needed to ionize a hydrogen atom. [5]
  2. (b)The difference in frequency of the Lyman alpha line in hydrogen and deuterium atoms. [5]
  3. (c)The magnetic moment of the electron. [5]
  4. (d)The spread in measurement of the π 0 mass, given that the π 0 lifetime is τ. [5]
(20)
Q. 5
  1. (a)An atom is capable of existing in two states: a ground state of mass M and an excited state of mass M + Δ. If the transition from ground to excited state proceeds by the absorption of a photon, what must be the photon frequency in the laboratory where the atom is initially at rest? [7]
  2. (b)Derive the energy levels of the hydrogen atom, from Coulomb's law and the simple quantization of angular momentum. [6]
  3. (c)In radio astronomy, hydrogen atoms are observed in which, for example, radiative transitions from n = 109 to n = 108 occur. What are the frequency and wavelength of the radiation emitted in this transition? [7]
(20)
Q. 6
  1. (a)Consider the elastic vibrations of a crystal with one atom in the primitive cell and calculate the frequency of an elastic wave in terms of the wavevector that describes the wave and in terms of the elastic constants. [12]
  2. (b)Describe vibrations of crystal. [8]
(12)
Q. 7
  1. (a)Discuss density of states in Three Dimension [8]
  2. (b)Describe Debye Model for Density of States [8]
  3. (c)Define phonon heat capacity. [4]
(20)
Q. 8

Write Notes on any TWO of the following:

  1. (a)Maxwell's Equations [10]
  2. (b)Magnetic Materials: (Ferro-Dia-Para) [10]
  3. (c)Black Body Radiation [10]
(20)

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About this paper

The 2023 CSS Physics paper set by the Federal Public Service Commission. Question wording only; questions marked “Not yet checked” have not been compared with the official paper yet. Open the official paper beside the questions to check any of them.

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