J & K CET Engineering J and K - CET Engineering Solved Paper-2009

  • question_answer
    The unit cell of a binary alloy composed of ,A and B metals, has a ccp structure with A atoms occupying the corners and B atoms occupying centres of each face of the cube. If during the crystallisation of this alloy, in the unit cell two A atoms are missed, the overall composition per unit cell is

    A) \[A{{B}_{6}}\]

    B) \[A{{B}_{4}}\]

    C)  \[A{{B}_{8}}\]

    D)  \[{{A}_{5}}{{B}_{24}}\]

    Correct Answer: B

    Solution :

     In the ccp structure, the A atoms are present at eight corners, so the number of A atoms per unit cell \[=8\times \frac{1}{8}\] \[=1\text{ atom}\] But two A atoms are removed per unit cell So, the number of A atoms per unit cell\[=6\times \frac{1}{8}\] \[=\frac{3}{4}\] The number of B atoms per unit cell \[=6\times \frac{1}{2}\]   \[=3\] \[\therefore \]The overall composition per unit cell \[={{A}_{3}}{{B}_{3}}\] or                            \[=A{{B}_{4}}\]


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