What is voltage sensitivity? State its SI unit.

Explanation

### Step-by-Step Solution:

1. **Understanding Voltage Sensitivity**:
- Voltage sensitivity refers to the measure of how much deflection (or angular displacement) occurs in a galvanometer or a similar device when a unit voltage is applied. It indicates the responsiveness of the device to changes in voltage.

2. **Defining Voltage Sensitivity Mathematically**:
- Mathematically, voltage sensitivity (S) can be expressed as:
\[
...