Question

Q.1 Differentiate between single crystal and polycrystalline.

Q.2 What do you mean by symmetry? Explain mirror symmetry

Answer 1

Single crystals have infinite periodicity, polycrystals have local periodicity. single crystal have same crystal parameter in entire crystal. but in polycrystalas crytal parameter is different in different range.

symmetry -

in translation or rotation of crystal if crystal repeat its structure than it is called symmetry in crystal.

A mirror symmetry operation is an imaginary operation that can be performed to reproduce an object.  The operation is done by imagining that you cut the object in half, then place a mirror next to one of the halves of the object along the cut. If the reflection in the mirror reproduces the other half of the object, then the object is said to have mirror symmetry. The plane of the mirror is an element of symmetry referred to as a mirror plane, and is symbolized with the letter m. As an example, the human body is an object that approximates mirror symmetry, with the mirror plane cutting through the center of the head, the center of nose and down to the groin.