Light is an electromagnetic radiation that moves at the speed of approximately 299 792 458 metres per second (m/s) in vacuum. This speed is maximum in our universe, no other object (having mass), can move with this speed. On the other hand, speed of sound is just 300 m/s. This is why you still see lightning before hearing thunder during a storm. Various properties of light are really unique, like it don’t need any medium to propagate, it always travels in straight line, it has dual nature (wave and particle), it has wavelength range from 400 nm to 700 nm and it consists of 7 different colors etc.
Our human eye can sense light as its wavelength is in the range of our visibility. Electromagnetic radiation has a broad variety of wavelengths, ranging from gamma rays with very less wavelengths to radio waves with wavelengths measured in meters. The wavelengths visible to humans, occupy a very small band within the wide spectrum, ranging from about 700 nanometers for red light to about 400 nanometers for violet light. The spectral regions adjacent to the visible band, infrared on one end and ultraviolet on the other, are often referred to as light.
From other properties of light, its dual nature is interesting. Light consists of tiny particles called photons. Each photon is considered as an energy packet having energy equal to hv (product of Plank constant and frequency of light). Speed of light is 3 x 108 m/s in vacuum.
Primary Colors of light
The primary colors of light are red, yellow, and blue. The secondary colors include orange, green and purple which can be created by mixing primary colors. Primary colors exist in light as well. However, these are not the same colors as we use in paint and markers. Red, green, and blue are the main colors of light. The secondary colors of light are cyan (blue and green combined), magenta (blue and red combined) and pink (made by combining green and red). The base of primary colors of light comes from the concept that when light is passed through a prism, it splits into 7 colors, each having different wavelength.
One interesting fact about light is that human eye can distinguish b/w the middle colors of spectrum more easily than others. Like if you go to a paint store and lay out all of the red and green paint choices, you’ll be amazed as you will be able to easily differentiate between the green shades than red. This is due to the fact that green is in the middle of the visible spectrum while red is in start of spectrum.
Properties of light waves
- Light is an electromagnetic wave which has fastest speed (3×108 m/s) in universe.
- It travels in straight line.
- Its velocity decreases by its actual value when enters certain medium.
- It has dual nature.
- Interference, scattering and diffraction prove its wave nature.
- Photo-electric effect, Compton Effect and pair production prove its particle nature.
It can show various properties when incident to some material, given below:
Reflection of Light
Reflection is a property of light which occurs when incident light strikes a material surface and material bounces off it, back to incident medium. The reflected light travels in straight line, but its direction is changed. The angle at which light is reflected is same at which light was incident i.e. the angle of incidence is equal to the angle of reflection. The angle of incidence means the angle that incoming light makes with a line perpendicular to the surface (also called normal). Similarly angle of reflection is the angle between the reflected light and normal.
Types of reflection: Reflection of light from a smooth surface is called specular reflection. Along a smooth surface, the normal always points the same way, so all of the light is reflected in the same direction. However, in case of a rough surface, normal at different spots along the rough surface points is in different directions due to which the reflected light travels in different directions. This is called diffuse reflection.
Refraction of light
Properties of light due to which, when light enters from one medium to another, then some of its part is reflected and remaining portion propagates in the second medium. The light ray changes its direction when enters in second medium, which is called refraction. This property of light is due to different speeds of light from different mediums.
In refraction, there can be 2 cases. Either refracted ray will bend towards normal or away from normal. If light enters from rarer medium to denser medium (with high refractive index), then it will bend towards normal. On the other hand if light enters from denser to rarer medium (with low refractive index) then it moves away from normal line.
Dispersion of light
Splitting of white light into its constituent colors caused by the wavelength of light and refractive index of the surface is known as dispersion of light. A prism can arrange the out coming beam into different colors in definite order, if incident ray consists of more than one wavelength. This is due to the fact that light has different speed through different mediums. Thus, a prism is a tool to disperse white light into its wavelengths.
Absorption of light
Light has a property to get absorbed by certain medium/material. Basically this light is converted into energy in that material. When the electrons of material atoms absorb energy, they get excited and move to higher levels. After 10-8 sec, they come back to ground state by releasing a photon of different energy than that of incident light. So, emitted light is of different color that incident ray.
Polarization of light
Polarization is from most important properties of light. Natural sunlight propagates in such a way that electric field vectors are perpendicular to the direction of propagation. This light will become polarized if electric field vectors are confined to a single plane. When filtration confines the electric field vectors to a single plane, the light is said to be polarized.
Sunglasses are best example to understand polarization of light. Polarizing filters are oriented vertically with respect to the frames on the lenses of sunglasses. The electric field vectors of the blue light waves in the figure are directed in the same direction as the polarizing lenses and they are therefore passed through it. The red light wave, on the other hand, is perpendicular to the filters and is thus blocked by the lenses. Polarizing sunglasses are very useful when driving in the sun or at the beach where sunlight is reflected from the surface of the road or water leading to glare that can be almost blinding.
Diffraction of light
It is a property of light by which it bends through some obstacle. However, the diffraction effects are more observable if the size of obstacle is of the order of the wavelength of light. This is the property due to which there is light in room even in evening time.
Frequently asked questions
Does light need a medium to travel?
No, since light is an electromagnetic wave, so it don’t need any medium to pass through. It can even travel through vacuum.
Does light travel in a straight line?
Yes, light always travel in straight line. Due to this reason, when some object is placed in path of light, we see its shadow.
Does light travel faster than sound?
Yes, light has maximum speed in this universe as it consists of massless photons. Nothing can travel faster than light. Speed of light is 3×108 m/s whereas speed of sound is 334 m/s.
Does light have mass?
No, light don’t has any mass. Since it consists of photons and photons have zero mass. So light also has no mass that’s why it has highest speed in universe.