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The regular three dimensional arrangement of points in a crystal is known as crystal lattice and the smallest repeating pattern in the lattice is called unit cell. The unit cells are characterised by the edge lengths a, b, c and the angles between them `alpha, beta and gamma` respectively. Based on this, there are seven crystal systems. In a cubic unit cell: `a=b=c and alpha = beta=gamma=90^(@)` The number of points in simple, body centred and face centred cubic cells are 1,2 and 4 respectively In both the hcp and ccp of spheres, the number of tetrahedral voids per sphere is two while the octahedral voids is one. In a face centred cubic cell, an atom at the face contributes to the unit cellA. 1 partB. `1//2` partC. `1//4` partD. `1//8` part |
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Answer» Correct Answer - B In fcc unit cell, an atom at the face centre is in contact with two unit cells. It contribution to the unit cell `=1//2` |
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