JEE Main & Advanced Physics Atomic Physics Question Bank Self Evaluation Test - Atoms

  • question_answer
    The wavelength \[{{K}_{\alpha }}\] of X-rays for two metals 'A' and ?B? are \[\frac{4}{1875R}\] and \[\frac{1}{675R}\] respectively, where 'R' is Rydberg constant. Find the number of elements lying between A and B according to their atomic numbers

    A)  3

    B)  1     

    C)  4

    D)  5

    Correct Answer: C

    Solution :

    [c] Using v\[\frac{1}{\lambda }=R{{\left( Z-1 \right)}^{2}}\left[ \frac{1}{n_{2}^{2}}-\frac{1}{n_{1}^{2}} \right]\] For \[\alpha \] particle, \[{{n}_{1}}=2,{{n}_{2}}=1\] For metal A: \[\frac{1875R}{4}=R{{\left( {{Z}_{1}}-1 \right)}^{2}}\left( \frac{3}{4} \right)\Rightarrow {{Z}_{1}}=26\] For metal B: \[675R=R{{\left( {{Z}_{2}}-1 \right)}^{2}}\left( \frac{3}{4} \right)\Rightarrow {{Z}_{2}}=31\] Therefore, 4 elements lie between A and B.


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