JEE Main & Advanced Sample Paper JEE Main - Mock Test - 9

  • question_answer
    When photon of energy \[4.25\text{ }eV\]strike the surface of a metal A, the ejected photoelectrons have maximum kinetic energy \[{{T}_{A}}eV\] and de-Brolie wavelength \[{{\lambda }_{A}}\]. The maximum kinetic energy of photoelectrons liberated from another metal B by photon of energy \[4.70\text{ }eV\]is \[{{T}_{B}}=({{T}_{A}}-1.50)eV.\]. If the de-Broglie wavelength of these photoelectrons is \[{{\lambda }_{B}}=2{{\lambda }_{A}},\] then

    A) the work function of A is \[3.40\text{ }eV\]

    B) the work function of B is \[6.75\text{ }eV\]

    C) \[{{T}_{A}}=2.00\,eV\]

    D) \[{{T}_{B}}=2.75\,eV\]

    Correct Answer: C

    Solution :

    \[{{K}_{\max }}=E-{{W}_{0}}\]
    \[\therefore \,\,{{T}_{A}}=4.25-{{({{W}_{0}})}_{A}}\]
    \[{{T}_{B}}=({{T}_{A}}-1.5)=4.70-{{({{W}_{0}})}_{B}}\]
    Equation (i) and (ii) gives \[{{({{W}_{0}})}_{B}}-{{({{W}_{0}})}_{A}}=1.95\,eV\]
    De Broglie wave length \[\lambda =\frac{h}{\sqrt{2mK}}\Rightarrow \lambda \propto \frac{1}{\sqrt{K}}\]
    \[\Rightarrow \,\,\frac{{{\lambda }_{B}}}{{{\lambda }_{A}}}=\sqrt{\frac{{{K}_{A}}}{{{K}_{B}}}}\Rightarrow \,2=\sqrt{\frac{{{T}_{A}}}{{{T}_{B}}-1.5}}\Rightarrow {{T}_{A}}=2eV\]
    From equation (i) and (ii)
    \[{{W}_{A}}=2.25\,eV\] and \[{{W}_{B}}=4.20\,eV\]


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