why copper is considered to be anisotropic in nature although the size of copper atoms arealmost equal?
Anistropy is determined by the arrangement of particles and not size of particles. Anisotropy basically means that certain physical properties such as electrical resistance, refractive index etc show different values when measured along different directions. Crytsalline solids are anisotropic in nature because of different arrangement of particles in different directions. Thus, because copper exits as crystalline solid, it is anisotropic in nature.