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Modern Physics Test - 3
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Modern Physics Test - 3
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  • Question 1/10
    4 / -1

    Order of magnitude of density of uranium nucleus is, [mp = 1.67 × 10–27kg]

    Solutions

    Nuclear density of an atom of mass number A,

  • Question 2/10
    4 / -1

    22Ne nucleus, after absorbing energy, decays into two aparticles and an unknown nucleus. The unknown nucleus is

    Solutions

    The new element X has atomic number 6. Therefore, it is carbon atom.

  • Question 3/10
    4 / -1

    Binding energy per nucleon vs mass number curve for nuclei is shown in the Figure. W, X, Y and Z are four nuclei indicated on the curve. The process that would release energy is

    Solutions

    KEY CONCEPT : Energy is released when stability increases. This will happen when binding energy per nucleon increases.

  • Question 4/10
    4 / -1

    Imagine an atom made up of a proton and a hypothetical particle of double the mass of the electron but having the same charge as the electron. Apply the Bohr atom model and consider all possible transitions of this hypothetical particle to the first excited level. The longest wavelength photon that will be emitted has wavelength λ (given in terms of the Rydberg constant R for the hydrogen atom) equal to

    Solutions

    KEY CONCEPT :

    For ordinary hydrogen atom, longest wavelength

    With hypothetical particle, required wavelength

  • Question 5/10
    4 / -1

    The electron in a hydrogen atom makes a transition from an excited state to the ground state. Which of the following statements is true ?

    Solutions

    NOTE : As the electron comes nearer to the nucleus the potential energy decreases

  • Question 6/10
    4 / -1

    Two radioactive materials X1 and X2 have decay constants 10λ and λ respectively. If initially they have the same number of nuclei, then the ratio of the number of nuclei of X1 to that of X2 will be 1/e after a time

    Solutions

  • Question 7/10
    4 / -1

    Electrons with energy 80 keV are incident on the tungsten target of an X-ray tube. K-shell electrons of tungsten have 72.5 keV energy. X-rays emitted by the tube contain only

    Solutions

    KEY CONCEPT :

    Energy of incident electrons is greater than the ionization energy of electrons in K-shell, the K-shell electrons will be knocked off. Hence, characteristic X-ray spectrum will be obtained.

  • Question 8/10
    4 / -1

    The electron emitted in beta radiation originates from

    Solutions

    Note : In a nucleus neutron converts into proton as follows n → p+ + e–1 Thus, decay of neutron is responsible for b-radiation origination

  • Question 9/10
    4 / -1

    The transition from the state n = 4 to n = 3 in a hydrogen-like atom results in ultraviolet radiation. Infrared radiation will be obtained in the transition

    Solutions

    For 2 to 1, 3 to 2 and 4 to 2 we get energy that  n = 4 to n = 3,

    I.R. radiation has less energy than U.V. radiation.

  • Question 10/10
    4 / -1

    The intensity of X-rays from a Coolidge tube is plotted against wavelength λ as shown in the figure. The minimum wavelength found is λC and the wavelength of the Kα line is λK. As the accelerating voltage is increased

    Solutions

    KEY CONCEPT :

    In case of Coolidge tube

    Thus the cut off wavelength is inversely proportional to accelerating voltage. As V increases, λc decreases. λk is the wavelength of K∝ line which is a characteristic of an atom and does not depend on accelerating voltage of bombarding electron since λk always refers to a photon wavelength of transition of e– from the target element from 2 → 1.
    The above two facts lead to the conclusion that λk – λc increases as accelerating voltage is increased.

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