Uttarakhand PMT Uttarakhand PMT Solved Paper-2011

  • question_answer
    In an atom, two electrons move around the nucleus in circular orbits or radii R and 4R. The ratio of the times taken by them to complete one revolution will be

    A)  8 :1              

    B)  1 : 4

    C)  4 : 1              

    D)  1: 8

    Correct Answer: D

    Solution :

     From Keplars law \[{{T}^{2}}\propto {{R}^{3}}\] \[\therefore \] \[\frac{T_{1}^{2}}{T_{2}^{2}}=\frac{R_{1}^{3}}{R_{2}^{3}},\] Here,    \[{{R}_{1}}=R\] and \[{{R}_{2}}=4R\] \[\therefore \] \[{{\left( \frac{{{T}_{1}}}{{{T}_{2}}} \right)}^{2}}={{\left( \frac{R}{4R} \right)}^{3}}=\frac{1}{{{4}^{3}}}\] \[\frac{{{T}_{1}}}{{{T}_{2}}}=\frac{1}{{{4}^{3/2}}}=\frac{1}{{{2}^{3}}}=\frac{1}{8}\] \[{{T}_{1}}:{{T}_{2}}=1:8\]


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