[heba1]

the conditions of the interference:
1)same frequency
2)same state of polarization(same plane)
3)collinear(same direction)
4)coherent(phase difference=constant)
but the conditions of standing waves:
1-same wavelength
2_same amplitude
3_opposite direction this is important condition one of wave is original wave and othere is reflected wave
so the conditions of interference doesnnot varied in standing waves