Viscous force is represented as `F=etaA(dv)/(dx).` Where,`eta` is proportionaly constant called as

Options

A. coefficient of viscosity
B. coefficient of velocity
C. surface tension constant
D. None of the above

Explanation

To solve the question regarding the proportionality constant `eta` in the equation for viscous force, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Viscosity**:
- Viscosity is a measure of a fluid's resistance to flow. It describes how thick or sticky a fluid is.

2. **Identifying the Equation**:
- The equation given is \( F = \eta A \frac{dv}{dx} \), where:
- \( F \) is the viscous force,
- \( \eta \) is the proportionality constant,
- \( A \) is the area,
- \( \frac{dv}{dx} \) is the velocity gradient.

3. **Proportionality Constant**:
- In the context of this equation, the constant \( \eta \) represents the fluid's viscosity.

4. **Naming the Constant**:
- The proportionality constant \( \eta \) is specifically referred to as the **dynamic viscosity** or simply **viscosity** of the fluid.

5. **Conclusion**:
- Therefore, the answer to the question is that \( \eta \) is called **viscosity**.