Question

The ratio $N_f/N_d$ is known as shape factor, where $N_f$ is the number of flow lines and $N_d$ is the number of equipotential drops. Flow net is always drawn with a constant b/a ratio, where b and a are distance between two consecutive flow lines and equipotential lines, respectively. Assuming that b/a ratio remains the same, the shape factor of a flow net will change if the

• A. upstream and downstream heads are interchanged
• B. soil in the flow space is changed
• C. dimensions of the flow space are changed
• D. head difference causing the flow is changed

Answer 1

The correct option is C dimensions of the flow space are changed

$Flowdependsongivenboundaryconditionsandiftheboundaryconditionsdoesnotchange,\frac{N_f}{N_D}willnotchange.$

If dimensions of flow space are changed, i.e. boundary condition is changed, it will result in change in shape factor.