Specular and Diffuse Reflection

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Introduction to Specular and Diffuse Reflection

One of the essential concepts due to which objects are visible to us is reflection. But how does this work? What is the phenomenon behind it? What are the different types of reflection? These are the basic concepts of science that every student must be well acquainted with. We provide insight into what reflection is and all that you need to know. This will help the students in getting a clear understanding of the concepts for better comprehension. We also provide these notes in PDF downloadable form allowing the students to study easily anytime, anywhere they want. 


Specular Reflection

It is also called regular reflection. This reflection usually takes place on smooth surfaces making the angle of incidence and angle of reflection equal. 


Diffuse Reflection

It is also called irregular reflection. This reflection usually takes place on rough surfaces, following which the angle of incidence and angle of reflection are unequal. 


Do all objects emit their own light? No. Rather, the visibility of objects is due to the reflection of light. Most objects reflect natural or artificial lights. The reflection of lights is tremendously impacted by the smoothness and roughness of the surface/object. 


Difference Between Regular Reflection and Diffused Reflection

Before understanding the difference, let us know the meaning of a beam and a ray of light. 


A beam of light consists of multiple individual light rays which are parallel to each other. And each ray of right follows the laws of reflection. But, this happens only in the case of smooth surfaces. On rough surfaces, every ray of light has a different orientation after reflection. 


Now, let us understand the difference between regular and diffuse reflection. 


Consider two different surfaces. Let one be a mirror (smooth surface), and the other be any rough surface (reddish). When white light is reflected on the mirror, it reflects all the white light components at the same angle as the incident light. The mirror does not absorb any component of any wavelength. However, this varies for a rough surface. When white light is reflected on the rough surface, it does not reflect all the wavelengths; rather, the blue and green are absorbed on the surface. Only the red light is reflected, causing the red colour of the surface. The colour is also visible due to the scattering of light on the surface. 


Specular and Diffuse Reflection Examples

There are several examples and applications of reflection that we experience daily. Here are some of the most interesting ones:

  • Driving on a wet road at night becomes difficult because of reflection. This happens as a result of the glare that is caused because of the headlights. The glare happens as a result of the specular reflection. While usually, diffuse reflection takes place on the surface, it does not happen in case of wet roads. Water fills up the roads' crevices, making it smooth, which further makes the light undergo specular reflection. 

  • Another common example can be observed with photography. Many times we have seen photographs in which the photographer captures the reflection of the surface in water. This also occurs as a result of specular reflection. The light which reflects off the water undergoes specular reflection allowing the photographer to capture the shot easily. 


Does Diffuse Reflection Follow the Law of Reflection?

The law of reflection states that, for a smooth surface, when a ray of light is incident on the surface, the angle of incidence is equal to the angle of reflection. 


In the case of diffused reflection, the law of reflection is not followed because the rays scatter in different directions. 


Applications of Specular and Diffuse Reflection

Diffuse reflection and specular reflection can be used in a variety of ways. However, we will focus on two of the more notable applications here:


One application involves the challenge of driving at night on a wet asphalt highway as opposed to a dry asphalt roadway. Most drivers are aware that driving at night on a wet road is difficult due to glare from oncoming headlights. Glare is caused by the specular reflection of an oncoming vehicle's light beam. Rough road surfaces generally generate diffuse reflection, but when wet, water fills the cracks and smoothes the surface. Light rays from an approaching car's headlights strike this smooth surface, undergo specular reflection, and remain focused in a beam. The driver notices an obnoxious glare as a result of this concentrated beam of reflected light. The light rays strike this surface and are reflected in a specular direction.


The second use is related to photography. Most of us have seen a snapshot of a magnificent natural scene with a calm body of water in the foreground taken by a photographer. If the water is calm, we may see the specular reflection of light from the subject of the shot. Light from the subject can either hit the camera lens directly or through a longer path that includes reflections from the water. Because the light reflected off the water is specularly reflected, the incident rays stay focused (instead of diffusing). As a result, the light may travel together to the camera's lens and generate a picture (an identical reproduction) of the subject that is powerful enough to be perceived in the photograph.


Laws of Reflection

The behavior of light is well-known to be very predictable. The law of reflection states that if a ray of light approaches and reflects off a flat mirror, the light's behavior as it reflects will follow a predictable pattern. The Law of reflection states that:

  • According to the law of reflection, the angle of the reflected ray is equal to the angle of the incident ray when reflected off a smooth finish surface with regard to the normal to the surface, which is a line parallel to the surface at the point of contact.

  • At the point of contact with the incident ray, the reflected ray is always in the plane defined by the incident ray and the normal to the surface.

FAQs (Frequently Asked Questions)

1. Can the readers read easily from a rough page or a glossy page? Why?

The readers can read easily from a rough page. This happens because the light rays scatter in various directions causing diffused reflection, making it easier to read. However, a glossy page's smooth surface leads to specular reflection making the pages shine and reflect. Due to these reasons, the readers tend to view and are attracted by the pictures on glossy pages.


2. Why do parallel rays scatter in different directions after undergoing reflection?

The parallel rays incident on a surface undergoes diffused reflection because every ray strikes the surface at different angles. This makes the orientation and normal different for all incident lights.

3. What does reflection mainly depend on, and how can it be changed?

Reflection mainly depends on the incident surface, and if you want to change the effect of reflection, you can do so by changing the angles of the incidence. This can lead to the scattering of light.

4. What Causes A Beam of Light to Scatter When It Hits A Rough Surface?

A beam of light is made up of a collection of parallel light beams. Each individual ray follows the law of reflection for every type of reflection. However, due to the roughness of the material, each individual ray collides with a surface that is oriented differently. Various rays have different normal lines at the moment of the incident. Individual rays disperse in different directions when they reflect off the rough surface according to the law of reflection. As a result, light rays strike the surface in a concentrated bundle, which is then diffused upon reflection. The rule of reflection controls each individual beam of light. Individual light rays, on the other hand, collide with a rough surface that has a different orientation. In other words, for different rays, the normal line at the site of incidence is varied. Individual rays disperse in different directions when they reflect off the rough surface according to the law of reflection.

5. What is irregular reflection?

Irregular waves are reflected when a light beam strikes a surface that is not completely smooth and polished, such as a wall, wood, or paper, and various areas of the surface reflect light in different directions. Due to the non-uniformity of the surface, parallel light rays are incident in various directions and reflect in opposite directions. The irregular or diffused reflection is a type of light reflection caused by an uneven surface. As a result, the uneven reflection is caused by irregularities in the reflecting surface. For instance, consider the reflection of light off the surface of a flowing stream.

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