Two-Point Source Interference Pattern

The interference of water waves in a ripple tank. There is destructive interference along the lines marked by N_{n} (Lines of Nodes) and constructive interference between these lines A_{n}(lines of antinodes).

Antinodes (X_{An}): **d _{2} - d_{1} = n l**; Nodes (X

The waves fronts from S_{1} and S_{2} combine at P. Assuming l >> d, such that **q** is very small (tan **q** = sin **q**), and by tan **q** = x/l, sin **q** = (d_{2} - d_{1})/d [d_{2} - d_{1 }= n**l**, for antinodes], we have approximately that

x = n(**l**l/d) (for antinodes)

and

x = (n + 1/2)(**l**l/d) ( for nodes).