12th Class Physics Atomic Physics Question Bank

done MCQs - Atoms Total Questions - 8

• question_answer1)
  \[{{\operatorname{O}}_{2}}\] molecule consists of two oxygen atoms. In the molecule, nuclear force between the nuclei of the two atoms
  A)
  is not important because nuclear forces are short-ranged. done clear
  B)
  is as important as electrostatic force for binding the two atoms. done clear
  C)
  cancels the repulsive electrostatic force between the nuclei. done clear
  D)
  is not important because oxygen nucleus have equal number of neutrons and protons. done clear
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• question_answer2)
  A set of atoms in an excited state decays.
  A)
  in general, to any of the states with lower energy. done clear
  B)
  into a lower state only when excited by an external electric field. done clear
  C)
  all together simultaneously into a lower state. done clear
  D)
  to emit photons only when they collide. done clear
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• question_answer3)
  Two H atoms in the ground state collide inelastically. The maximum amount by which their combined kinetic energy is reduced, is
  A)
  10.20 eV done clear
  B)
  20.40 eV done clear
  C)
  13.6 eV done clear
  D)
  27.2 eV done clear
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• question_answer4)
  Taking the Bohr radius as \[{{a}_{0}}\] = 53 pm, the radius of \[{{\operatorname{Li}}^{++}}\]ion in its ground state, on the basis of Bohr's model, will be about                             
  A)
  53 pm. done clear
  B)
  27 pm. done clear
  C)
  18 pm. done clear
  D)
  13 pm. done clear
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• question_answer5)

  The binding energy of a H-atom, considering an electron moving around a fixed nuclei (proton), is

  \[\operatorname{B}=\frac{m{{e}^{4}}}{8{{n}^{2}}\varepsilon _{0}^{2}{{h}^{2}}}\] (m = electron mass). If one decides

  to work in a frame of reference where the electron is at rest, the proton would be moving around it.  By similar arguments, the binding energy would be

  \[\operatorname{B}=\frac{m{{e}^{4}}}{8{{n}^{2}}\varepsilon _{0}^{2}{{h}^{2}}}\] (M= proton mass).

  This last expression is not correct because

  A)
  n would not be integral. done clear
  B)
  Bohr-quantisation applies only to electron done clear
  C)
  the frame in which the electron is at rest is not inertial. done clear
  D)
  the motion of the proton would not be in circular orbits, even approximately. done clear
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• question_answer6)
  The simple Bohr model cannot be directly applied to calculate the energy levels of an atom with many electrons. This is because
  A)
  of the electrons not being subject to a central force. done clear
  B)
  of the electrons colliding with each other. done clear
  C)
  of screening effects. done clear
  D)
  the force between the nucleus and an electron will no longer be given by Coulomb's law   done clear
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• question_answer7)
  For the ground state, the electron in the H-atom has an angular momentum = h, according to the simple Bohr model. Angular momentum is a vector and hence there will be infinitely many orbits with the vector pointing in all possible directions. In actuality, this is not true,
  A)
  because Bohr model gives incorrect values of angular momentum. done clear
  B)
  because only one of these would have a minimum energy. done clear
  C)
  angular momentum must be in the direction of spin of electron. done clear
  D)
  because electrons go around only in horizontal orbits. done clear
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• question_answer8)
  Choose the correct alternative from the clues given at the end of each statement:
  A)
  The size of the atom in Thomson's model is .......... the atomic size in Rutherford's model. (much greater than/no different from/much less than) done clear
  B)
  In the ground state of ........... electrons are in stable equilibrium, while in .......... electrons always experience a net force. (Thomson's model/Rutherford's model) done clear
  C)
  A classical atom based on ............. is doomed to collapse. (Thomson's model/Rutherford's model) done clear
  D)
  An atom has a nearly continuous mass distribution in ............. but has a highly non-uniform mass distribution in ............ . (Thomson's model/Rutherford's model) done clear
  E)
  The positively charged part of the atom possesses most of the mass in ............. . (Rutherford's model/both the models) done clear
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