When a wave undergoes reflection at a denser medium, what will be the phase change?

When a wave undergoes reflection at a denser medium, it experiences a phase change of 180 degrees or π radians. This means that the wave is inverted or flipped over.

Here are the steps to understand this:

1. When a wave travels from a less dense medium to a denser medium (like from air to water), and it hits the boundary at an angle, it slows down and bends towards the normal line. This is called refraction.

2. However, if the wave hits the boundary straight on (perpendicular or normal incidence), it will not bend but it will slow down.

3. In both cases (refraction or normal incidence), if the wave is reflected back into the less dense medium, it undergoes a phase change of 180 degrees.

4. This phase change means that the wave is inverted. If you imagine the wave as a series of peaks and troughs, after reflection at a denser medium, the peaks become troughs and the troughs become peaks.

5. The reason for this phase change is due to the change in speed of the wave. In a denser medium, the wave slows down. When it is reflected, this slower speed results in a phase change.