Reflection and refraction are important concepts that help us understand how waves behave.

1. Reflection: Reflection happens when a wave bounces off a surface. The law of reflection says that the angle at which the wave hits the surface (the angle of incidence) is the same as the angle at which it bounces off (the angle of reflection). You can think of it like this: If you throw a ball at a wall, the angle it hits the wall is the same as the angle it comes back at you.

2. Refraction: Refraction is when a wave changes direction as it passes from one material to another. This change happens based on Snell's Law. This law tells us that the angles of the waves and how much they bend can be described with this idea:

   • Different materials have different abilities to bend waves, which we call the indices of refraction.
   • When a wave moves from one material to another, the angles at which it enters and bends are connected.

3. Critical Angle: The critical angle is a special angle when light moves from a denser material (like water) to a less dense material (like air). It can be figured out with a simple formula. If light hits the surface at this angle, it will reflect completely instead of passing through.

Understanding these ideas is important in optics. They help us predict how waves will act when they encounter different materials.