Content Curator
Difference between reflection and refraction can be explained by stating reflection as the phenomenon of bouncing back of the light ray after hitting a surface whereas refraction refers to the bending of the rays of light on passing on from one medium to another.
| Table of Content |
Refraction Definition
Refraction is the phenomenon of bending light when it passes from one transparent medium to another. The medium in which the velocity of light is larger is called optically rarer medium and the medium in which the velocity of light is smaller is called the optically denser medium. The phenomenon of refraction is the result of different velocities of light in different mediums.
When a ray of light travels from an optically denser medium to an optically rarer medium, it gets bent towards the normal. Also when a ray of light travels from an optically rarer medium to a denser medium, it gets bent away from the normal. During the process of refraction, the velocity and wavelength of light change from their initial value, whereas the frequency of the light ray remains the same as that of the initial value.
First law of refraction – It states that the incident ray, refracted ray, and the normal to the interface of incidence point, all lie in the same plane.
Second law of refraction – This law is also known as the Snells Law. The law states that the ratio of the sine of the angle of incidence and the sine of the angle of refraction is a constant. The law is applicable for a specific pair of mediums and the color of light used.
Sin(i)/Sin(r) = Constant = n2/n1
The term n2/n1 is called the refractive index of the second medium with respect to the refractive index of the first medium.
Absolute Refractive Index
It is defined as the ratio of the velocity of light in a vacuum with respect to the velocity of light in a medium.
n = c/v
c = Speed of the light in vacuum
v = speed of the light in a medium
The Refractive index provides a measure of the velocity of light in a certain medium.
Reflection Definition
The process of bouncing back off a ray of light after striking a medium is called reflection. The crux of reflection is that the atoms of the reflecting surface absorb energy from the source and radiate energy in the form of light rays. Reflection happens in the same medium, the refractive index will be the same.
There are two different types of reflection: Regular reflection and irregular reflection.
Regular Reflection
Regular reflection occurs when the interface is optically plane. The Incident light and reflected light will have the same pattern.
Regular reflection normally occurs in objects like a plain mirror, and stainless steel.
Irregular Reflection
Irregular reflection is normally observed when the interface is a rough surface. This phenomenon is also called diffused reflection. The parallel rays of light incident on a rough surface will be reflected in different directions. No definite images are produced in irregular reflection, the person will be able to see the rough interface instead of the source of the light. Irregular reflection generally occurs on the surface of a wall, piece of paper, or a blackboard.
Laws of Reflection
The law states that the angle of incidence is equal to the reflection on an optically smooth surface. The incident ray, reflected ray, and the normal drawn at the point of incidence, all lie on the same plane
Difference between Reflection and Refraction
| Reflection | Refraction | |
| Definition | Bouncing back of light rays in the same direction in the same medium | The process of changing the direction or bending of light when propagating from one transparent medium to another |
| Types | Two types of reflection are regular reflection and irregular or diffused reflection | Refraction is only of one type. |
| Interface | Generally shown in the mirrors or other optically plane surfaces | Generally shown in the lenses |
| Change in the speed of light | Speed of the light is not affected in reflection | Speed of the light changes accordingly in optically denser and rarer mediums. |
| Angle of incidence | The angle of incidence is equal to the angle of reflection during the formation of an image. | The angle of incidence is unequal to the angle of refraction during the formation of an image. |
| The wavelength of light ray | The wavelength of the light ray does not change | The wavelength of light changes with the change in medium. |
| The direction of light ray | The direction of light remains the same | Light rays get bend when the medium changes |
Things to Remember
- Difference between reflection and refraction is a part of CBSE class 10 science syllabus.
- It comes under unit 3 Natural phenomena and this unit carries a total of 23 periods and 12 marks.
- Refraction occurs due to the different velocities of light in different media.
- Reflection is of two types, regular and irregular reflection.
- During refraction, velocity, and wavelength of light ray change, whereas frequency remains the same.
- Refractive index is the measure of the velocity of light in a specific medium, it is dimensionless.
- The angle of incidence, angle of reflection is the same in reflection, but not in refraction.
Sample Questions
Ques 1. State Snell's law? (1 mark)
Ans. The law states that the ratio of the sine of the angle of refraction to the sine of the angle of refraction is a constant.
Ques 2. What happens to the incident light rays in a diffused reflection? (1 mark)
Ans. The incident rays are reflected in different directions after a diffused reflection.
Ques 3. Define the term absolute refractive index? (1 mark)
Ans. The absolute refractive index is the ratio of the velocity of light in a vacuum or air to the velocity of air in a medium.
Ques 4. Explain how the direction of light rays changes when the medium is changed? (1 mark)
Ans. When a light ray moves from an optically denser medium to a rarer medium, it bends towards the normal and when the light propagates from an optically rarer medium to a denser medium, it bends away from the normal.
Ques 5. What happens when a light ray strikes an obstacle? (1 mark)
Ans. When a light ray strikes an obstacle in its path, a portion of it gets reflected, another portion gets refracted and the remaining portion of the light ray gets absorbed by the obstacle.
Ques 6. What do you mean by refraction and reflection of light? (1 mark)
Ans. Reflection is the phenomenon of bouncing back of the light ray after hitting a surface whereas refraction refers to the bending of the rays of light on passing on from one medium to another.
Ques 7. What are the objects used to identify reflection and refraction of light? (1 mark)
Ans. Reflection is generally observed on mirrors or plane optical surfaces, but refraction is observed in lenses.
Ques 8. State the difference between reflection and refraction in terms of the angle of incidence? (1 mark)
Ans. The angle of incidence is equal to the angle of reflection but unequal to the angle of refraction during the formation of an image.
Ques 9. WHat is the speed of light in reflection and refraction? (1 mark)
Ans. The speed of the light is not affected in reflection but it changes accordingly in optically denser and rarer mediums in case of refraction.
Ques 10. State any two differences between reflection and refraction. (2 marks)
Ans. Two differences are:
| The wavelength of the light ray does not change | The wavelength of light changes with the change in medium. |
| The direction of light remains the same | Light rays get bend when the medium changes |
Comments