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Shivam Sharma posted an Question
September 07, 2020 • 23:05 pm 30 points
  • CSIR NET
  • Earth Sciences

"point group" in crystallography is characterized by a set of symmetry operations such that all points in a crystal are affected by it no point in a crystal is

"Point Group" in crystallography is characterized by a set of symmetry operations such that all points in a crystal are affected by it no point in a crystal is affected by it at least one point in a crystal is affected by it at least one point in a crystal is unaffected by it What are the Miller indices of a plane that intercepts each of the crystallographic axes X, Y and Z, at 20 A? (Assume a primitive unit-cell with the dimensions a = 5 A,b =2Å and c = 4 A.) (111) (524) (425) (542)

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  • Shivam sharma

    Explain 1st question

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    point group is a group of geometric symmetries (isometries) that keep at least one point fixed. In simple words; point group is a combination of symmetry and even after application of all symmetry elements there should be a point which will remain unaffected by operations.

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    Sajan sarthak Best Answer

    1.At least one point is unaffected by it. 2.524 is the Miller indices

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    Explain 1st question

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    ok

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    In simple words we need at least one reference point to see the symmetric operation whether it's axis , point or plane.

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    This group is called the point group of that molecule, because the set of symmetry operations leave at least one point fixed (though for some symmetries an entire axis or an entire plane remains fixed). In other words, a point group is a group that summarizes all symmetry operations that all molecules in that category have.[9] The symmetry of a crystal, by contrast, is described by a space group of symmetry operations, which includes translations in space.

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    Rahul kumar best-answer

    Q1. (D) Atleast one point in a crystal is unaffected by it Q2. (B). (524) The intercepts are 4a, 10b, 5c. To get the miller indices we have to reverse the intercept and then normalise it. Reverse of intercept: 1/4, 1/10, 1/5 Normalising (multiplying by 20 in all) will give: (524) So miller indices is (524)

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