Reflection phase change

Okay, so when you look in a mirror, you see your reflection, right? That's because the mirror reflects light - the light bounces off of you and goes into the mirror, then bounces back out and goes into your eyes.

Now, imagine that instead of you looking at yourself in a mirror, there's a beam of light traveling through the air. If it hits something - like a wall, or a mirror - some of the light will bounce back and some will keep going. The amount of light that bounces back depends on what the thing it hits is made of, and how it's shaped.

In some materials - like glass, water, or air - the light can also change direction when it hits the material. This is called refraction.

So, sometimes when light hits a surface, like a wall or a mirror, it bounces back and changes direction at the same time. This is called a phase change. It happens because the light wave that's bouncing back is inverted (kind of like turning upside down), so when it combines with the wave that's still travelling forward, they cancel each other out and create a "null" or "zero" wave - basically, a place where the light waves completely cancel each other out.

This can have some interesting effects. For example, if you have a plane wave (like a laser beam) hitting a flat mirror at an angle, the reflected wave will be "out of phase" with the incoming wave - meaning the peaks and valleys of the waves won't line up anymore. This can cause interference patterns, where the light waves can either reinforce each other or cancel each other out, depending on where they are in relation to each other.

So, in short, reflection phase change is when light waves bounce off of a surface and invert their phase, cancelling out parts of the original wave and creating interesting interference patterns.