The phase difference between two points A and B on a given wavefront separated by distance \( \lambda \) is:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 0
A wavefront is defined as the surface of constant phase: the locus of all points that oscillate in the same phase. So any two points on the same wavefront are in phase, however far apart they are along it.
\( \displaystyle \Delta\phi = 0 \)
The separation \( \lambda \) gives a phase difference of \( 2\pi \) only for two points along the direction of propagation, not for two points on one wavefront.
NCERT (2026-27):
Huygens Principle – “… Clearly, all points on such a circle are oscillating in phase because they are at the same distance from the source. Such a locus of points, which oscillate in phase is called a wavefront; thus a wavefront is defined as a surface of constant phase.”