Why amorphous solids are called isotropic whereas crystalline solids are called anisotropic ?

Answer

To understand why amorphous solids are called isotropic while crystalline solids are called anisotropic, we can break down the explanation into clear steps:

### Step-by-Step Solution:

1. **Definition of Amorphous Solids**:
- Amorphous solids are materials that lack a well-defined long-range order in their atomic arrangement. This means that the arrangement of atoms is random and does not repeat in a regular pattern.

2. **Properties of Amorphous Solids**:
- In amorphous solids, properties such as electrical conductivity, refractive index, and thermal expansion are uniform in all directions. This means that if you measure these properties in any direction, you will get the same value.

3. **Isotropy**:
- Because the properties of amorphous solids are identical in all directions, they are described as isotropic. Isotropic materials exhibit the same physical properties regardless of the direction in which they are measured.

4. **Definition of Crystalline Solids**:
- Crystalline solids, on the other hand, have a well-defined long-range order. The atoms in crystalline solids are arranged in a highly ordered and repeating pattern.

5. **Properties of Crystalline Solids**:
- In crystalline solids, properties such as electrical conductivity, refractive index, and thermal expansion vary depending on the direction of measurement. For example, the conductivity might be higher in one direction than in another.

6. **Anisotropy**:
- Since the properties of crystalline solids differ in different directions, they are described as anisotropic. Anisotropic materials exhibit different physical properties when measured along different axes.

7. **Conclusion**:
- Therefore, amorphous solids are called isotropic because their properties are the same in all directions, while crystalline solids are called anisotropic because their properties vary with direction.