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JEE Main & Advanced Sample Paper JEE Main - Mock Test - 11

  • question_answer
    Photoelectric effect experiments are performed using three different metal plates p, q and r having work functions \[{{\phi }_{p}}=2.0eV,\] \[{{\phi }_{q}}=2.5eV\] and \[{{\phi }_{r}}=3.0eV,\] respectively. Alight beam containing wavelengths of \[550\text{ }nm,\] \[450\text{ }nm\] and \[350\text{ }nm\] with equal intensities illuminates each of the plates. The correct \[I-V\] graph for the experiment is [Take\[hc=1240\text{ }eV\,nm\]]

    A)           

    B)

    C)          

    D)

    Correct Answer: A

    Solution :

    The energy possessed by photons of wavelength \[550\,\,nm\] is \[\frac{1240}{550}=2.25eV\]
    The energy possessed by photons of wavelength \[450nm\] is \[\frac{1240}{450}=2.76\,eV\]
    The energy possessed by photons of wavelength \[350nm\] is \[\frac{1240}{350}=3.54eV\]
    For metal plate p:\[{{\phi }_{P}}=2eV.\]
    All the wavelengths are capable of ejecting electrons. Therefore, the current is maximum. Also as the work function is lowest in p, the kinetic energy of ejected electron will be highest and therefore, the stopping potential is highest.
    For metal plate q: \[{{\phi }_{q}}=2.5eV\]
    Photons of wavelength \[550\text{ }nm\]will not be able to eject electrons and therefore, the current is smaller than p.
    The work function is greater than q therefore the stopping potential is lower in comparison to p.
    For metal plate r: \[{{\phi }_{r}}=3\,eV\]
    Only wavelength of \[350\text{ }nm\]will be able to eject electrons and therefore, current is minimum. Also the stopping potential is least.


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