What is Poisson's ratio? On what does its magnitude depend?

(N/A) Poisson's ratio is defined as the ratio of lateral strain to longitudinal strain produced in a material when it is subjected to a tensile or compressive force.
When a tensile force is applied to a wire,its length increases (longitudinal strain),while its cross-sectional diameter decreases (lateral strain).
Conversely,when a compressive force is applied,the length decreases,and the diameter increases.
Mathematically,Poisson's ratio $(\mu)$ is given by:
$\mu = -\frac{\text{lateral strain}}{\text{longitudinal strain}}$
If the original diameter is $d$ and the change in diameter is $\Delta d$,the lateral strain is $\frac{\Delta d}{d}$. If the original length is $L$ and the change in length is $\Delta L$,the longitudinal strain is $\frac{\Delta L}{L}$.
Therefore,$\mu = -\frac{(\Delta d / d)}{(\Delta L / L)}$.
Since it is a ratio of two strains,it is a dimensionless and unitless quantity.
The magnitude of Poisson's ratio depends solely on the nature of the material of the body.