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c P I F C 2. Tetragonal P I 3. Orthorhombic P I F C 4. Hexagonal P 5. Trigonal P 6. Monoclinic P C 7. Triclinic P Shiv K. Gupta Department of Applied Mechanics, IIT Delhi Couldn’t find his photo ML Frankenheim 15 lattices 18111863 Auguste Bravais 14 lattices Your photo 13 lattices Shiv K. Gupta Department of Applied Mechanics, IIT Delhi What is the basis for classification of lattices into 7 crystal systems and 14 Bravais lattices? Shiv K. Gupta Department of Applied Mechanics, IIT Delhi Lattices are classified on the basis of their symmetry Shiv K. Gupta Department of Applied Mechanics, IIT Delhi What is symmetry? Shiv K. Gupta Department of Applied Mechanics, IIT Delhi If an object is brought into selfcoincidence after some operation it said to possess symmetry with respect to that operation. Symmetry Shiv K. Gupta Department of Applied Mechanics, IIT Delhi Rotational symmetry A rectangle es into selfcoincidence by 180 degrees rotation Shiv K. Gupta Department of Applied Mechanics, IIT Delhi If an object e into selfcoincidence through smallest nonzero rotation angle of ? then it is said to have an nfold rotation axis where ?0360?n