Discussion
A propagating wave is reflected at a barrier. The phase of the wave changes in the act of reflection by :
Answer: C
The phase changes by \(\pi\).
When a wave is reflected at a rigid barrier, or more generally at a boundary with a denser (higher impedance) medium, the reflected wave is inverted. For a string fixed at one end, the displacement at the fixed point must stay zero, which forces the reflected wave to cancel the incident one there: a phase change of \(\pi\) (half a wavelength). Light reflected from a medium of higher refractive index behaves the same way.
A change of zero occurs only at a free end or a rarer medium, which a barrier is not, and a shift of \(\pm\pi/2\) is not produced by simple reflection at such a boundary.
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