Assuming that path difference of λ gives constructive interference: Similar to the path difference of λ, path difference of 2λ, 3λ … nλ also constructively interfere, as displayed in Figure 2.08.

All Constructive interference:

Figure 2.08: Schematic of path difference between more planes.

It may be noted that if the path difference between Ray-1 and Ray-2 is λ then the path difference between Ray-1 and Ray-3 is 2λ and Ray-1 and Ray-4 is 3λ, etc.

Similarly, one could go across different planes as shown in Figure 2.09.

Figure 2.09: Schematic of path difference going across planes.