BCECE Engineering BCECE Engineering Solved Paper-2015

  • question_answer
    The threshold frequency for certain metal is\[3.3\times {{10}^{14}}Hz.\] If light of \[8.2\times {{10}^{14}}Hz\]frequency is incident on the metal, then the cut-off voltage of the photoelectric current will be

    A) \[\text{3V}\]                    

    B) 4 V

    C) \[\text{2 V}\]                                    

    D) \[~\text{2}.\text{5 V}\]

    Correct Answer: C

    Solution :

    In photoelectric effect, energy is conserved. In photoelectric effect, Einstein's equation is given by Photon energy = kinetic energy of electron + work function i.e.                          \[hv=e{{V}_{s}}+h{{v}_{0}}\] where, \[{{V}_{s}}\] is the stopping potential and \[{{v}_{0}}\] is the threshold frequency \[\therefore \]  \[{{V}_{s}}=\frac{h}{e}(v-{{v}_{0}})\]                                      ? (i) Given,    \[{{v}_{0}}=3.3\times {{10}^{14}}Hz,v=8.2\times {{10}^{14}}Hz\] \[h=6.6\times {{10}^{-34}}J-s,e=1.6\times {{10}^{-19}}C\] Substituting these values in Eq. (i), we get \[{{V}_{s}}=\frac{6.6\times {{10}^{-34}}({{8.210}^{14}}-3.3\times {{10}^{14}})}{1.6\times {{10}^{-19}}}\] \[{{V}_{s}}=\frac{6.6\times 4.9}{1.6}\times {{10}^{-1}}=2V\] \[\Rightarrow \]               \[{{V}_{s}}=2V\]


You need to login to perform this action.
You will be redirected in 3 sec spinner