Light- Reflection, Refraction, Dispersion, and Scattering
Light, Reflection, Refraction, Dispersion, and Scattering are the properties of light, reflection of light is bouncing back of the light ray when it incidents on an opaque surface. Refraction of light is the deviation of a light ray from its own way and dispersion is splitting up of light ray into seven colors, when light ray enters the fluid, the particles of medium spread the light around them, this phenomenon of light is known as scattering.
The branch of physics in which the characteristics of light are studied is known as Optics. The concept that light is a wave had been discovered in ancient Greece in 5 BC to 3 BC. The reflection, diffusion, and vision were summarized by Euclid (300 -275 BC) in his book Optics. The observations of astronomy have led the theory of light in modern optics. Initially, the scientist observes the varying size of the moon, the position of the stars and visual perceptions. Newton in 17 th century also embedded one more concept when he introduced that light is made of particles, this theory was opposed by Huygens and advocates the theory of light as a wave because of the light’s characteristic of reflection and refraction, later Maxwell introduces that light is an electromagnetic wave. In the 20 th century, the greatest scientist Einstein concluded to the fact from Hertz’s discovery of the photoelectric effect of light that light is made of the photon. In modern physics, the light is supposed as a wave due to the characteristics of reflection, refraction, diffraction, scattering, and interference in contrast to the concept of light as particles due to its phenomenon of dispersion and the photoelectric effect, therefore it is supposed that light has dual nature,it behaves as particles and as a wave.
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Here we are discussing the following phenomenon of light.
1- The reflection
1- The reflection
We see everything in this world due to the presence of light, light rays fall on the object and then send back to our eyes and image of the object formed on the retina of our eyes and thus we become capable to see the object. The sun is the largest source of light to us. it can be said that the Sun is the largest source of energy on the earth, it is because of the virtue of light reflection we use microscope, telescope, radar, etc. When light rays fall on the surface of an object, the surface of the object sends back light rays by a certain angle to another direction, in other words, the phenomenon that light ray bounces off an object is known as reflection.
The rule of reflections
(1) When light rays fall on a smooth surface of an object, the incident ray reflected ray and the normal to the surface on the incident point all lies in the same plane
(2) When light rays fall on a smooth surface of an object, the angle between the incident ray and normal known as the incident angle is always equal to the angle between normal and reflected angle known as the reflected angle.
When light rays fall on a rough surface then these are reflected in all directions and rules of reflection are not followed, it is called diffused reflection.
Application of reflection of light- (i) We become capable to see everything due to the reflection of light.
(ii) The 30% radiations of total light energy exposed to the earth are reflected back to space regulates the temperature in the earth, this phenomenon of reflection of light keeps us away from the excess temperature in the earth.
When light travels from one medium to another medium it deviates from its own path this phenomenon of light is known as refraction. When the light ray transports from rare medium to dense medium it bents towards the normal and when light rays transport from dense medium to rare medium then it bents away from the normal.
Rules of refraction
(1) When light rays refracted from one medium to another medium then the incident ray, refracted ray and normal lies on the same plane.
(2) The ratio between the sine of an incident angle to the sine of the refracted angle is always constant for a given pair of medium or given pair of the color of light.
Where i is incident angle and r is refracted angle this constant shows the index of refraction. If light rays transport from a medium to another medium which is denser then this constant increases because of the decrease in refracted angle and when light travels from dense medium to rare medium then the constant decreases with the increase in refracted angle. This constant tells how much light ray is refracted so it is also known as the refractive index of one medium with respect to another medium.
The angle of refraction depends on the speed of the light between two medium if as compared to the incident angle the angle of refraction is less means the speed of light is slower and if the angle of refraction is more then the speed of light is more, therefore the refractive index of one medium with respect to another medium is given by the ratio of speed between two mediums.
Let the speed of light in medium 1 is and in medium 2 is then refractive index of the medium 2 with respect to medium 1 is given by
The Refractive index of medium 1 with respect to medium 2 will be as follows
Absolute refractive index
When the light ray passes to any medium from the vacuum or air then the refractive index of the medium the ratio between the speed of light in air or vacuum to speed of light in the medium is known as the absolute refractive index. It is represented by μ.
Where c is the speed of light in the vacuum and v is the velocity of light in the medium
When a light ray travels from a denser medium to rare medium then the angle of incidence for which the angle of refraction become 90°. This is the angle if the increased whole of the incident light reflected back to the denser medium which is known as total internal reflection.
The causes of diamond shine
The diamond is an allotropic form of carbon, carbon has four valance electrons, each carbon atoms form covalent bonds with one another and arranged in the shape of a tetrahedron. In this way whole of the diamond, crystal is made of tiny prisms when light enters into it converted into 7 colors. The critical angle of the diamond is 24° which is the least among all substances, this led the total internal reflection of the light is maximum inside it. The refractive index of diamond is higher i.e 2.42. Therefore the causes of the diamond shines are the total internal reflection, the higher amount of refraction and dispersion inside it.
The splitting of light rays into seven colors is known as the dispersion of light. The dispersion of light occurs because all colors have different wavelengths and different speeds, when light enters in a refracting medium these colours deviates from the original path of the light ray so all colors are refracted in increasing order of wavelength i.e VIBGYOR, V-Violet, I-Indigo, B- Blue, G- Green, Y-Yellow, O-Orange, R-Red.
Scattering occurs due to the individual particles available in the medium, the particles absorb the light and then scatter it in all directions except to the direction of incoming rays. The scattering of light depends on the size of particles. light ray enters into the particle that is absorbed and particles get illuminated. Particles of small size like molecules absorb the lower wavelength colors from the spectrum of light then scatter the same color of light. The color of the sky looks blue because molecules of the gas available in the atmosphere absorb and scatter lower wavelength colors, violet, indigo blue and green among them primary colors are blue and green makes the color of the sky .