This question was previously asked in

HPPSC AE Civil 2016 (PWD-HIMUDA) Official Paper

Option 4 : Permeameter length is changed

**Explanation:**

**Flow net:**

(i) The entire pattern of flow lines and equipotential lines is referred as a flow net. It is the solution of Laplace's equation for relevant boundary conditions. Thus, a flow net is a graphical representation of the head and direction of seepage at every point.

(ii) **Flow net **is a **function of only boundary condition** and is **independent of permeability, head loss, or number of flow lines and equipotential lines**. Hence the flow length will alter if permeameter length is changed.

__Additional Information__

**Properties of flow net:**

(i) Flow lines and equipotential lines meet each other orthogonally.

(ii) There can be no flow across the flow line and velocity of flow is always perpendicular to equipotential lines.

(iii) Area bounded between two adjacent flow lines is called flow channel or flow path and quantity of water flowing through each channel is same.

(iv) Area bounded between two adjacent equipotential lines and adjacent flow lines are referred to as a flow field.

(v) For isotropic medium, flow field is rectangular which may either be linear or curvilinear.

(vi) Loss of head between two equipotential lines i.e. equipotential drop remain constant for all the equipotential lines.