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Explain how each sphere (particles) contributes in formation of particular unit cell. |
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Answer» Solution : To study the contribution of atoms or particles per unit cell following POINTS are noted : (i) Each ATOM located at the corner of the unit CELLS is shared between eight adjacent unit cells i.e., four unit cells of same layer and four unit cells of the immediate upper or lower layer. Hence, `(1/8)^(th)`part of the atom belongs to a one only unit cell.  (ii) An atom present at the centre of the face of the cubic unit cell is shared EQUALLY by two unit cells having the COMMON face. Hence, the atom present at the centre of the face of a cubic unit cell contribute only `(1/2)` of a particular cell  An atom located at the centre of body of a cubic unit cell belongs to that particular cell only. Hence, the atom at body centred of unit cell contributes 1 to a particular unit cell.  (iv) An atom located at the centre of edge of a cubic unit cell is shared equally by four unit cell. Hence, the atom at edge centre of unit cell contributes `(1/4)^(th)` to a unit cell.  .
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