Light has some interesting phenomena when passing through different objects. The characteristics of light are even peculiar when we observe in different media. Here, we will deal with two phenomena of light: Reflection and Refraction which are integral parts of waves and optics.
Understanding Reflection: How Light Bounces Back
Light is counted to have the properties of both wave and matter. One of the fundamental properties of light when it is regarded as a wave is the reflection. The light coming from a source is fully absorbed by the transparent object and allows it to pass through them. The light can only transmit partially through the translucent object. Lastly, opaque objects block light from passing through them. These three types of objects existing in nature show either fully or partially the phenomenon of reflection.
Reflection is the process by which light meets the surface of a medium and returns to that same medium. Thus, reflection is responsible for making any object visible to us. Another point to remember is that if an object allows all of the light to pass through it, the object cannot be observed, discarding the process of reflection, whose suitable example is air. Thus, to be visualized, an object should either completely or partially show the process of reflection.
- Terms used in reflection:
It is important to note about some useful terms before going through the phenomenon of reflections. Some of them are listed below:
- Reflecting surface:
The surface where the incoming ray of light hits and the process of reflection appears is known as the reflecting surface.
- Incident ray:
The ray of light that comes from the luminous source and interacts with the reflecting surface is called an incident ray.
- Reflected ray:
The reflected ray is a beam of light that returns to the same medium after meeting a surface.
- Normal:
It is a perpendicular line drawn above the surface at the point of incidence or reflection.
- Angle of incidence:
It is the angle made by the incident ray and the normal at the point of incidence, denoted by ‘i’.
- Angle of reflection:
It is the angle made by the reflected ray and the normal at the point of reflection, denoted by ‘r’.
- Glancing angle:
The angle of the incident light and the surface of reflection is defined as glancing angle which is denoted by ‘g’.
- Angle of deviation:
It is the angle between the original direction of the incident ray and the reflected ray, which is denoted by ‘ẟ’.
Exploring Refraction: How Light Bends
When the type of medium is different while the passage of light, it shows some other features. The ray of light appears to deviate from the initial path when the medium changes, creating an illusion of a false position of the object to an observer. This process of bending light when media are different is known as refraction of light. For example, when an object is placed in water, it appears to be bent.
- Terms used in Refraction:
We regard incident ray to be equal in both cases.
. Other terms used in refraction are as follows:
- Refracted ray:
The incident ray, after entering another medium, changes its direction and takes another way than the incident ray. This emerging ray after entering another medium because of the change in speed of light is known as refracted ray.
- Angle of Refraction:
The angle of refraction is defined as the angle formed by the refracted light and the normal. It is also denoted as ‘r’
- Rarer medium:
It is a medium for which the speed of light is a bit higher than the other medium.
- Denser medium:
It is a type of medium where the speed of light is relatively less.
- Refractive index:
The refractive index compares the speed of light in a medium with the air.. Mathematically,
μ = c/v [Equation 1]
Where,
- μ is the refractive index.
- c is a constant quantity which means the speed of light in air and
- v differs as per the medium.
- Real depth and Apparent depth:
The actual depth of an object from the surface of another medium when immersed from one medium to another is known as real depth. Yet the false depth of the object that appeared when viewed from the other medium is known as apparent depth. For example, when a coin is immersed in water, it seems to be raised slightly, which is called the apparent depth. Whereas the true position of the coin is called the real depth.
- Critical angle:
When light passes from denser to rarer medium, a specific condition arises where the angle of incidence is such that the corresponding angle of refraction tends to be 90°. This angle of incidence where it gives 90° of refraction angle is known as the critical angle.
- Total internal reflection:
When we keep on increasing the angle of incidence further than the critical angle, the light completely comes back to the same medium. This situation is defined as total internal reflection. We have to remember that for total internal reflection, the light must travel from denser to rarer medium, and the angle of incidence must go above the critical angle.
Key Differences Between Reflection and Refraction:
There are certain laws of reflection and refraction, which are written below:
- Laws of Reflection:
- The incident ray, the reflected ray and the normal at the point of incidence (or reflection) all are on the same plane.
- The angle made by the incident ray with the normal and that made by the reflected ray and the normal (angle of incidence and angle of reflection) are equal (i = r).
- A ray of light incident normally on a surface is reflected back to the same initial path of the incident ray.
- Laws of Refraction:
- When a beam of light moves from a rarer to a denser medium, it deviates towards the normal (i > r).
- When a beam of light moves from a denser to a rarer medium, it deviates away from the normal (i < r)
- The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant.
sin i/sin r = μ [Equation 2]
This statement is also known as Snell’s law.
Real-Life Examples of Reflection in Daily Life
We experience reflection in our daily lives. Some of them are listed below:
- Eyes: The reflection of light made by our eyes is the reason we have eye-sight. Everything around us is made visible because of the reflection of light by our eyes.
- Mirrors: They are used in ordinary cases as looking glass and for advanced scientific purposes as in periscope, kaleidoscopes, etc.
- Water: When a beam of light falls on water, it refracts nearly all of the light. However, some portion of light is sent back and shows reflection.
- Jewelry: Various ornaments and accessories shine and are observable because they show reflection.
- Coloured objects: A monochromatic ray of light is incident on the surface of the object, which is almost absorbed, and only some portion is reflected back at different wavelengths. This variation in wavelengths introduces different colours of objects.
- Metals: Metals are natural light-reflecting objects and have a shining property.
Common Instances of Refraction Around Us
The most common examples of refraction in everyday circumstances are as follows:
- A pencil dipped inside water appears to be bent.
- A bowl drowned in water seems to be up.
- When light rays fall on a prism, it is refracted at different angles.
- Pickles kept in a glass jar appear to be larger than their actual size because of refraction.
- The lens of human eyes too refracts light and sends it to the brain through the optic nerve.
- The glittering of stars happens by the refraction of light as light beam passes through various layers of atmosphere.
- Diamonds glitter due to total internal reflection, which is also a special case of refraction.
The Science Behind Mirrors and Lenses
- Types of mirrors: Mirrors are often made up of highly polished surfaces that bounce light back. They completely follow the principle of reflection.
- Plane mirror: It is a smooth surface that produces a virtual image of an object. The image formed is inverted. A clear image is formed by plane mirrors.
- Concave mirror: Its surface is curved inward and produces a magnified view of the image. It is also called the converging mirror. The image formed may be real or virtual, which depends on the position of the object.
- Convex mirror: Its surface is curved outward and produces a diminished view of an object.It diverges any light falling on it. A virtual and erect image if formed by this mirror.
- Types of lenses:
- Lenses are composed of transparent things with curving surfaces. Lenses are made up of different objects; that’s why when light in an air medium enters the lens, it is bent following the principle of refraction. The types of lenses are :
- Concave lens: It is also known as a diverging lens that produces diminished, virtual, and erect images. It is narrower in the center than the borders, and the parallel beams of light entering it deviate from the focal point. A common eye defect called myopia or shortsightedness is corrected using this lens.
- Convex lens: The the incoming parallel rays of light after reaching the lens meet at the focal point. The center is thicker than the edges. A magnified, real (or virtual) and inverted image is formed by a convex lens. It is used in cameras, magnifying glasses, and eye-glasses to treat the defect of hypermetropia (long-sightedness).
Applications of Reflection and Refraction in Technology
Various scientific equipment and technologies utilize the principle reflection and refraction of either one or both in combination.
Applications of Reflection:
- In Vehicles: Vehicles use convex mirrors as rearview and side mirrors so that the image of the vehicles behind is diminished and is viewed clearly. Hence, it enables safety on roads.
- In telescopes, microscopes, and periscopes, a concave mirror is used in telescopes to obtain magnified views of distant stars. Similarly, plane mirrors are used in telescopes and periscopes to get better illumination without any obstacle.
- Optical Fibers: Light signals are passed through thin fibers in telecommunications, endoscopy, and sensors employing the principles of reflection.
- Laser Cavities: Mirrors are used inside laser cavities that reflect and amplify light and produce coherent light beams.
Applications of Refraction
- To correct eye-sight: concave lenses are used for the correction of shortsightedness, whereas convex lenses are used for the correction of longsightedness.
- In cameras, convex lenses are used to focus light to form sharp images on sensors.
- Microscopes and Telescopes: Lenses are used to magnify the image of tiny objects or distant objects by refracting light.
- Magnifying Glasses: Convex lenses are used to produce magnified images of objects for close observation.
- Prisms: Prisms show the phenomena of refraction and separate light into various spectrums for chemical analysis.
- Fiber Optics: In telecommunications, data is sent by refraction and total internal reflection, providing high-speed internet.
- Projectors: Projectors use lenses to refract light and form large images on the screens.
- Optical sensors: Lenses and prisms are used by devices such as photodiodes to focus light for accurate measurements.
Combined Applications of Reflection and Refraction
- Optical Instruments: Devices such as spectrometers and interferometers need both reflection and refraction for performing precise measurements.
- Binoculars: Binoculars use mirrors or prisms for adjusting light paths by reflection and lenses for magnification utilising refraction.
- Compact Discs (CDs) and DVDs: Laser light reflects from the disc surface in CDs and DVDs, and refraction sends light to read data.
- Camera Lenses: The camera focuses light by refraction and enhances clarity of image by using reflecting coatings to minimize light-flare.
- Advancements in optics:
There are also several modern technologies developed on the basis of reflection and refraction. Some of them are pointed out below:
- Holography: Holography is a technology where 3D images are created based on reflection and refraction of light. These images are used as a source of entertainment and also for security purposes.
- Smart Mirrors: A smart mirror is a complex reflective surface that has been digitally merged to provide more features and information than an ordinary mirror.
- Photonic Crystals: Photonic crystals successfully modify light in fiber optics and lasers by making use of refraction and reflection.
Experiments to Demonstrate Reflection and Refraction
Here are some simple experiments that can be performed at home or in a classroom. Reflection and Refraction Using a Water Surface
Materials:
- Transparent water vessel
- Laser pointer
- White sheet of paper
- Ruler
Procedure:
- Firstly fill the vessel with water and set on a level surface.
- Set the laser towards the water’s surface at some angle.
- Observe the light as it reflects off the surface and refracts into the water.
- Sketch the reflected and refracted rays on a white paper sheet.
Observations:
- The reflected ray follows the laws of reflection.
- The refracted ray bends depending on the angle of incidence and the difference in the refractive index of air and water.
- Bending of Light Through a Prism
Objective: To observe the dispersion and refraction of light.
Materials:
- Glass prism
- White light source (e.g., flashlight with white light)
- Dark room
- White screen or wall
Procedure:
- Put the prism in a dark room.
- Light the white light beam at one side of the prism at an angle.
- On a white screen or wall, see the light that leaves the prism’s opposite end.
Observations:
- Light deviates as it passes through the prism (refraction).
- The white light scatters into its spectrum due to the varying refractive indices for different wavelengths.
These are the two simplest ways of experiments to study the phenomena of reflection and refraction.
Conclusions
Reflection and refraction are two basic properties of light that describe how it interacts with various materials and surfaces. Refraction illustrates how light bends as it passes through different media, whereas reflection enables light to bounce back from surfaces. These phenomena serve as the foundation for many optical technologies, such as mirrors, lenses, and fiber optics, and are crucial to comprehending natural phenomena. We can better understand how light behaves and how it is used in both ordinary life and forefront scientific instruments by researching these concepts.
References
Rao, K. R. (2001). Back to basics: Reflections on refraction. Current Science, 81(8), 875-879.
Andrews, S. S. (2023). Refraction. In Light and Waves: A Conceptual Exploration of Physics (pp. 211-245). Cham: Springer International Publishing.
Lekner, J. (2016). Theory of reflection. Springer Series on Atomic, Optical, and Plasma Physics, 87.
Yu, N., Genevet, P., Kats, M. A., Aieta, F., Tetienne, J. P., Capasso, F., & Gaburro, Z. (2011). Light propagation with phase discontinuities: generalized laws of reflection and refraction. science, 334(6054), 333-337.
https://www.geeksforgeeks.org/physics/difference-between-reflection-and-refraction/
https://byjus.com/physics/difference-between-reflection-and-refraction/
