Define Poisson’s ratio ? Does it have any unit ?

Explanation

### Step-by-Step Solution

1. **Definition of Poisson's Ratio**:
Poisson's ratio (denoted as \( \mu \)) is defined as the ratio of the lateral strain to the longitudinal strain when a material is deformed elastically.

2. **Understanding Strains**:
- **Longitudinal Strain (\( E_{longitudinal} \))**: This is the change in length per unit original length when the material is stretched. It can be expressed as:
\[
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