Light and its Fundamentals
In the previous post we discussed what is optical fiber communication and how does it work and, in this post, we will discuss Light and its Fundamentals.
Introduction to Light:
Light is made up of electromagnetic radiation that can be detected by the human eye. This radiation is made up of different wavelengths, which we see as different colors. The human eye can see a small portion of this electromagnetic spectrum, which we call visible light.
Colors of Visible Light:
Visible light is made up of red, orange, yellow, green, blue, and violet light. Each of these colors has a different wavelength. Red light has the longest wavelength, while violet light has the shortest wavelength. Light waves travel through the air and are absorbed and reflected by objects. When light waves hit an object, some of the waves are reflected off the object. This is how we see objects.
Interaction of Light with Objects:
The color of an object is determined by the wavelength of light that is reflected off of the object. For example, a red object reflects red light and absorbs all other colors. White objects reflect all colors, while black objects absorb all colors.
Importance of Light:
Light is essential for us to see the world around us. Without it, we would be in complete darkness. It can be used to communicate, to signal danger, to illuminate dark areas, and to provide warmth. It can also be used for medical purposes, such as in lasers and x-rays.
Light Rays:
When a lamp is turned on, it gives us light. Apart from this, there are other light sources such as candles, fluorescent tube lights, LEDs and the sun etc. Light travels in all directions from the light-emitting object. The light traveling in any one direction in a straight line is called a ray of light. A group of light rays given out from a source is called a beam of light.
Behavior of Light Rays:
Suppose we have a light source such as a light bulb and a light ray from it hits an object surface. Now what will happen
When a light ray is strikes an object, it can do one of three things depending on the object’s material: reflect, refract, or become absorbed into the material (Out of these three we will discuss refract and reflect). If light reflected off an object, it still travels in straight lines, but in a new direction. If the light enters our eyes, we see the object (i.e., our eyes can detect light).
Reflection of Light
Introduction to Reflection:
Reflection is the act of reflecting something back at itself. In physics, reflection occurs when a wave hits an object, bounces off, and returns to its original position. This can happen for many reasons, but most often it happens when light hits a shiny surface like metal or water.
Mirrors as Reflective Surfaces:
A mirror is a perfect example of how reflection works. The process of reflection occurs when light tries to pass from one medium to another and is bounced back by that medium.
Types of Reflection:
When we talk about reflection, we are talking about how light bounces off surfaces. There are two types of reflections: specular and diffuse. Specular reflections happen when the angle of incidence equals the angle of reflection, and there is no change in brightness or color. Diffuse reflections happen when the angles are not equal, and there is a change in brightness and color. Here I have mentioned two terms angle of incidence and angle of reflection, let’s understand them in simple terms.
Understanding Key Terms:
If we draw a line that goes straight up at 90 degrees to the mirror surface, is called the normal and a ray of light that hits mirror surface is called incident ray. The angle which the incident ray makes with the normal is called angle of incidence. The angle which the reflected ray makes with the normal is called angle of reflection. The law of reflection states that when light strikes a mirror, it will be reflected off at an equal but opposite angle to the original ray.
Refraction of Light
Introduction to Refraction:
Refraction, similar to reflection, involves the behavior of waves, particularly light waves. However, instead of bouncing back, as in reflection, refraction occurs when a wave bends around an object. A common observation of refraction is seen when looking at water droplets on a window, where light passing through glass changes direction due to differing air densities inside and outside the glass.
Understanding Refraction in Simple Terms:
You may have seen refraction happen when looking at water droplets on a window. When light passes through the glass, it changes direction due to the different density of air inside and outside the glass. Refraction can be seen when looking at a stick that is partially submerged in water, since the stick appears to bend at the surface of the water.
In other and simpler words, Refraction is the bending of light as it passes from one medium to another OR When light moves from one medium to another it changes speed and direction. That change in direction is called refraction.
Factors Influencing Refraction:
The amount of bending depends on the wavelength of the light, the angle at which it strikes the object, and the composition of the object. When a light passes from one medium to another, the light may change speed. The speed of light in a vacuum is about 299,792 kilometers per second (186,282 miles per second). The speed of light in water is about 225,000 kilometers per second (140,000 miles per second), and in glass it is about 199,000 kilometers per second (124,000 miles per second).
Effect of Medium Density on Light Speed:
1. Varied Mediums for Light Travel:
There are many different types of mediums that light can travel through. Some of these mediums are denser than others, and some are less dense. The amount of density of a medium will affect how the light travels through it.
2. Impact of Medium Density on Light Speed:
In a denser medium, light travels more slowly. This is because the denser medium will have more particles that the light has to interact with. This interaction will cause the light to slow down.
On the other hand, light will travel more quickly through a less dense medium. This is because there are fewer particles for the light to interact with. This means that the light will not be slowed down as much, and will be able to travel faster.
3. Refraction and Medium Transition:
For example, light will travel more slowly through a denser medium. When light passes from a denser medium to a less dense medium, the light is refracted towards the normal. When light passes from a less dense medium to a denser medium, the light is refracted away from the normal.
Index of Refraction:
Light is refracted only when it hits a medium at an angle, so if light goes straight (angle of 90° or along the normal) down into a substance it will continue to move straight down.
The index of refraction is a number that describes how light bends when it passes through a material. The higher the index of refraction, the more the light bends.
Calculation Example:
The index of refraction measures how much light bends in a material. It’s calculated by dividing the speed of light in a vacuum by the speed of light in the material. For instance, if vacuum speed is 3.00 x 10^8 m/s and material speed is 2.00 x 10^8 m/s, the index of refraction is 1.50. This number is always greater than 1.
Total Internal Reflection
Critical Angle and Reflection:
The critical angle is the angle of incidence at which light is no longer refracted, but is instead reflected. This angle is dependent on the index of refraction of the material; the higher the index of refraction, the smaller the critical angle. When the angle of incidence is greater than the critical angle, the light is said to be “total internal reflected.”
Total Internal Reflection and Fiber Optic Cables:
Total internal reflection is what allows for fiber optic cables to work. Light is injected into one end of the cable at a low angle of incidence. The light then bounces around inside the cable, undergoing total internal reflection at the interfaces between the core and cladding. This process continues until the light reaches the other end of the cable, where it is then emitted.
if you want to simulate the reflection, refraction and total internal reflection you can try PhET Interactive Simulations.
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