# maximum phase difference between two waves

#### PG1995

Joined Apr 15, 2011
816
Hi

I believe the maximum phase difference possible between two waves is 90°. Suppose we have two waves. When the wave A is just starting out which means its phase is 0∏ or 2π, the wave B is at its 3∏/4 (correction: 3∏/2) phase. From wave A's perspective, wave B is lagging behind by 90° but from wave B's perspective the wave A is leading it by 90°. Would there be a difference mathematically? Perhaps, in one way, phase difference is 90° but in other way it's -90°. Please help me with it. Thanks.

Regards
PG

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#### steveb

Joined Jul 3, 2008
2,436
Why can't there be a 180 degree phase difference?

#### samin

Joined Oct 14, 2011
32
I think it is 180 degree.

Because the two waves could be in opposition of phase, then it is 180 degrees.

Check the attached example.

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#### strantor

Joined Oct 3, 2010
5,226
From wave A's perspective, wave B is lagging behind by 90° but from wave B's perspective the wave A is leading it by 90°.
would be leading by 270 degrees, no?

#### t_n_k

Joined Mar 6, 2009
5,455
This raises an interesting problem. Suppose you were looking at the two waves [A & B] on an oscilloscope - where they are time dependent sine functions with the same frequency.

What is the maximum phase difference you would be able to discern on the scope? As stevb & samin note, the maximum difference you could possibly see would be 180° when the two signals are in exact anti-phase.

Could you discern a difference of B leading A by 270°? Would it not simply appear to an observer that wave B leads A by 90°.

BTW PG1995: In your post you suggested a case situation where "..the wave B is at its 3∏/4 phase." Keep in mind that 3∏/4 is 135°.

#### THE_RB

Joined Feb 11, 2008
5,438
The maximum phase difference is 359.99 (repeating) degrees.
The maximum +/- phase difference is 180 degrees.
Easy.