Optics

# light reflection

Reflection of light is an optical phenomenon in which a visible electromagnetic wave strikes a given medium, returning to the original medium in which it propagated. There are two types of reflection, called regular and diffuse reflection .

## light reflection concept

Reflection of light happens when a ray of light strikes a reflective surface and returns to its original medium. This phenomenon allows us to see all bodies that do not produce their own light , called secondary sources of light or simply illuminated bodies.

In the total absence of light, these bodies would not be visible, therefore, in order to see them, they need to reflect the light coming from some light source. It is worth saying that not all objects that reflect light allow us to see our reflection. In such cases, we say that the reflection suffered by the light is diffuse .

When we look at a reflective surface and we can see some reflection, we say that the light is undergoing a regular reflection , which can also be called specular reflection and is the one in which we can see the formation of reflected images.

## regular reflection of light

Regular reflection of light occurs when the incident and reflected light ray obey the laws of light reflection , as we will see later. The following figure helps us understand how the regular reflection of light works. Watch:

In regular reflection, the angle of incidence of light is equal to the angle of reflection. This angle, in turn, is measured with respect to the direction normal to the plane of reflection.

## diffuse reflection of light

In diffuse reflection, the incident and reflected light rays do not form the same angle with respect to the normal direction and do not need to be contained in the same plane. The following figure illustrates a situation where diffuse reflection of light occurs. Watch:

## Examples of light reflection

Check out some examples in which we can observe the reflection of light.

• When we see our reflection in a mirror, rear view mirror or even on the surface of a puddle of water, we are observing the regular reflection of light.
• When we see any object that is not emitting its own light, but we do not see our reflection in it, we are observing the diffuse reflection of light.

## Laws of light reflection

The laws of light reflection indicate what conditions are necessary for regular reflection of light to occur.

• The first law of reflection states that incident and reflected light rays must form the same angle with respect to the normal direction.
• The second law of light reflection states that incident and reflected light rays must be contained in the same plane.

## Solved exercises on the reflection of light

Question 1 — A ray of light is incident at an angle of 25º in relation to a reflecting surface, thus undergoing a regular reflection. The angle of reflection of this ray of light is equal to:

a) 45th

b) 65th

c) 90º

d) 115th

Resolution:

Since the angle of incidence and the angle of reflection are equal in regular reflection, the angle formed between the reflected ray of light and the surface is 65º (remember that between the surface and the normal direction there is a 90º angle); therefore, the correct alternative is the letter B .

Question 2 — For regular reflection of light to occur, it is necessary that:

a) the incident and reflected light rays are contained in different planes.

b) the incident and reflected light rays form different angles with respect to the normal.

c) the incident and reflected light rays are contained in the same plane.

d) the incident and reflected light rays are equally polarized.

Resolution:

According to the 2nd law of reflection , for regular reflection of light to occur, it is necessary that the incident and reflected light rays are contained in the same plane, so the correct alternative is the letter C