Waves can be reflected at the boundary between different mediums. When a wave is reflected, it stays in the same medium instead of passing through.
Light reflection is when light waves bounce off a surface and change direction.
Reflection from smooth, flat surfaces is known as specular reflection. In this case, light meeting the surface in one direction is reflected in only one direction. This can include surfaces like mirrors or calm water and in specular reflection, an image can form.
An example of specular reflection is in the picture below.
Specular reflection is taking place because the water is smooth and calm. So, there is a clear image of the trees and mountains in the water.
Diffuse reflection occurs when a surface is rough. Each light ray is still reflected normally, but the reflected light is scattered in many different directions due to the rough surface. This is why an image does not form when diffuse reflection occurs.
For example, when you look at a rough wall, you do not see your reflection.
We can use ray diagrams to show how light travels and what happens when it reaches a surface (boundary).
In the diagram above, the grey block is a mirror, which is called a plane mirror because it is a flat surface. The dashes at the bottom show the back side of the mirror.
The incident ray hits the surface of the mirror and is reflected back as the reflected ray.
In ray diagrams, we draw a vertical line at a 90° angle to the mirror, which is called the normal. We use this line to calculate the angle of incidence and the angle of reflection.
The law of reflection states that:
The angle of incidence = The angle of reflection
So, if the angle of incidence is 40°, the law of reflection states that the angle of reflection is also 40°. They must always be equal.