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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 distances 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

- upstream and downstream heads are interchanged
- soil in the flow space is changed
- dimensions of the flow space are changed
- head difference causing the flow is changed