Angle of Reflection: Definition & Formula

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  • 0:05 Law of Reflection and…
  • 1:06 Specular and Diffuse…
  • 1:53 Reflection and Plane…
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Lesson Transcript
Instructor: Nissa Garcia

Nissa has a masters degree in chemistry and has taught high school science and college level chemistry.

When light hits an object, it bounces off the object's surface and reaches our eyes. All that we see around us is made possible by a phenomenon called reflection. This lesson covers the definition, angle, types of reflection, and the law of reflection.

Law of Reflection and Angle of Reflection

Our surroundings--the sky, trees, people, and our image in the mirror --are made visible to us by reflection, where light bounces off the surface of the object and this light reaches our vision. Most of these objects do not emit light, but we can see them because light is reflected off of these objects.

Let us consider a ray of light hitting the surface, which is called the incident ray. The incident ray comes in at an angle, which is called the angle of incidence. The ray of light that bounces off the surface is called the reflected ray, and the angle at which the reflected ray bounces off the surface is called the angle of reflection.

According to the law of reflection, the angle of incidence is equal to the angle of reflection. Here, we see an illustration of the law of reflection, where the vertical dashed line is normal (perpendicular) to the surface. The angles of incidence and reflection are measured relative to the dashed line.

 Figure 1: Law of reflection - the angle of incidence is equal to the angle of reflection.

We can, therefore, say that the law of reflection states that the angle of incidence (theta-i) is equal to the angle of reflection (theta-r).

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Specular and Diffuse Reflection

Reflection occurs on both smooth and uneven surfaces. If multiple incident rays parallel to each other reach a smooth surface, such as still water, the reflected rays are all bounced off at the same angle. This results in a clear image known as specular reflection on the surface.

Figure 2: reflection on a smooth surface resulting in a specular reflection

Some examples of objects that give off specular reflections are plane mirrors, smooth glass windows, and clear, still water.

When reflection occurs on uneven surfaces, the law of reflection is still observed, with multiple incident rays bouncing off at multiple reflected rays due to the texture of the surface. Light is diffused and a diffuse reflection occurs.

A diffuse reflection results from light reflected on rough/uneven surface

Some examples of objects that give off diffuse reflections are textured glass and a rough asphalt road.

Reflection and Plane Mirror Images

A plane mirror is a smooth surface that produces a specular reflection. It is very smooth, so when light hits the surface, the resulting image is not distorted. How does the law of reflection cause us to see an image of ourselves when we look into a mirror?

Figure 4: Production of an image from a plane mirror

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