# Do the amplitudes have to be the same for two waves to be in phase and construct?

## Main Question or Discussion Point

Just curious...I know that constructive interference occurs when two waves are "in phase" but does this mean that the heights of the waves have to be the same? In other words... can two waves that are in phase with each other constructively interfere if one wave has a higher amplitude than the other?

Related Classical Physics News on Phys.org
George Jones
Staff Emeritus
Gold Member
Just curious...I know that constructive interference occurs when two waves are "in phase" but does this mean that the heights of the waves have to be the same?
No.

In other words... can two waves that are in phase with each other constructively interfere if one wave has a higher amplitude than the other?
Yes.

Thank you, that has been bothering me for a while...

rbj
it might not have been an issue, but i'm thinking that a good thing to point out is that the two waves don't have be perfectly in-phase to be constructive interference. but they have to be within 90o of each other to constructively interfere. only for totally destructive interference (where the result is nothing) must both the phase and amplitude be exactly something (180o outa phase and equal amplitude). otherwise either the phase or amplitude can be sloppy.

I intend to experiment with interference and superpostioning and its good to know that i don't have to be dead on for it work. Thanks...

James R