Behavior of light worksheet

Behavior of light worksheet
White Light Prism effect

Light is that form of energy that helps us see things. Without light, trees and plants cannot survive, and without trees, life on earth is impossible. Light is a type of radiation energy that does not look like other energies.

Therefore, we are able to see only those objects which have light energy. Light has been a mystery to humans since the beginning. Different philosophers have had different views regarding the appearance of objects. Six centuries before Christ, Pythagoras said that many small particles are produced from objects and when

Discovery of light

If the opaque object placed in the path of light is very small, then light shows a tendency to turn along its edges instead of running in a straight line – this effect is called diffraction of light. The optics, which use rays based on simple linear behavior, then fail. Light is considered as a waveform to explain phenomena like diffraction. Again, in the early 20th century it became clear that the wave theory of light is insufficient in its interaction with the matter of light and light often behaves like the flow of particles. This confusion about the true nature of light continued for a few years until the modern quantum theory of light emerged, in which light was neither considered a wave nor a particle. This new theory established harmony between the relative properties of light and the wave nature.

When they fall on the eyes, things start to appear to us. According to Empedoclees, only small particles released from the eyes make the object viewable. Plato told that celestial rays come out of the eyes, which meet the rays of the sun and fall on the object and then we see the object. Aristotle knew the rules of walking in direct lines of light and its reflection.

After this, there was no significant progress in the subject of optics for 1000 years. Around the 11th century, the famous Arabic philosopher Alhazen studied the structure of the eyes and explained the works of the eyes. He was well known in the rules of refraction. It is said that in the 13th century, Roger Baker made visionaries and microscopes by combining lenses.

Rare and dense media
The ability of a medium to refract light can also be expressed by its optical density. Optical density has a definite connotation. It is not the same as mass density. The terms rare medium and dense medium mean ‘optically rare medium’ and ‘optical dense medium’ respectively. When can we say that one medium is optically dense compared to another medium, the other with less refractive index is the optically rare medium. The speed of light in a rare medium is higher than that of a dense medium. Therefore, the beam of light that travels through the sparse medium into the dense medium slows down and tilts towards the normal. When it moves through the dense medium into the sparse medium, its speed increases and it moves away from the normal.

Many small and big inventions of light occurred in the 16th century, but the 17th century can be called the critical period of optics. In this era, scientists like Newton, Heigens and Roemer made important inventions in the field of optics. Newton proposed the Karpas cooler theory according to which light moves as particles. Hygens gave the wave theory of light and Roemer found the velocity of light in 1675.

James Clarke Maxwell stated in 1873 that when the magnetic or electric field in a circuit changes at a frequency, it is not limited to the circuit alone, but oscillations in the circuit produce a type of waves, which are called electric They are called magnetic waves, which propagate around the velocity of light. The diffusion of these waves is due to the periodic motion of the electric and magnetic fields. With these vibrations, electromagnetic waves propagate at the speed of light. When the frequency of electromagnetic or magnetic vibrations is in a certain range, we see these vibrations as visible light. The color of the light depends on the frequency of these vibrations. In 1887, Hertz proved that the electromagnetic waves had all the properties of light by generating electromagnetic waves in the laboratory. Electromagnetic waves have the following properties:

These waves can also move in vacuum and their velocity in vacuum is equal to the velocity of light.
Electromagnetic waves are transverse waves.
In addition to visible light, there are some waves which we cannot see, but can experience. Gamma rays, X rays, ultraviolet rays, infrared rays and radio waves are all electromagnetic waves.

In 1900 AD, Max Planck, while working on the radiation of the black body, observed that the experimental findings of the radiation and the prevailing theoretical deliberations do not match. He discovered a new theory called the quantum theory of light.

According to this theory, energy does not move continuously but in the form of packets. These small units of energy are called quantum. Scientists like Einstein etc. accepted the importance of this theory and also believed that light moves in the form of very small particles, called photons.

There are some phenomena in nature that cannot be explained on the basis of quantum theory. Scientists were confused by this dual nature of light, after all, how they considered light. In the end, this problem was solved with a new, regular and mathematical theory.

This new theory was formulated in 1924 by Heisenberg and Schrödinger. According to the French scientist, D. Broglie, ‘There is no difference in considering an electron as a particle or as a wave, it is only a wave of probability and the square of its amplitude is present in a particular place (in the system). Explains the possibility. ”Today’s scientist does not worry that light is a wave or particle.

Radiation Radiation

If energy is transmitted from one place to another without any fluid medium, it is called radiation. Radiation refers to electromagnetic radiation. Electromagnetic waves do not require any medium to move, nor do they have any effect on electric and magnetic fields. X-rays, infrared rays, radio waves and photons etc. are all radiation. Each radiation has its own wavelength and accordingly its properties. Visible light is also a type of radiation that is visible to the eyes. This is called visible radiation. The wavelength of visible radiation ranges from about 4000A ° to 8000A °. We cannot see the radiation whose wavelength is less than 4000A ° or more than 8000A °. Such radiations are called invisible radiation, such as infrared rays, ultraviolet rays, gamma rays, X rays etc.

Published items

Illuminated objects: Those illuminated by their own light, such as the sun, electricity, bulbs etc.

Unadulterated items: Those objects which do not have their own light but are visible when light comes, such as chair, table, book etc.

Transparent objects: Through which light rays pass through, such as glass.

Semi-observable objects: Objects on which some part of them gets absorbed by light rays and some part gets out, like oiled paper.

Non-opaque objects: Objects from which rays of light cannot come out, such as metals, wood etc.


By placing an opaque object in front of a light source, the black shape formed behind the object is called a shadow. It depends on the shape of the light source. If the source is a point source, then the shadow formed is hidden and if the source is large, then the shadow formed is called the shadow.

Transmission of light

Although the light rays travel in a straight line, there is definitely some turning on the edges of the barriers. The feel is very short due to the wavelength being extremely small. The phenomenon of light turning along the barriers is called diffraction of light.

Speed ​​of light

The speed of light is different in different mediums. The speed of light is highest in air and vacuum. The speed depends on the refractive index of the medium. The higher the refractive index of the medium, the lower the speed of light in a medium, to find the speed of light in a medium, use the formula -u = c / μ, where u is the speed of light, c in the vacuum of light Speed ​​and μ is the refractive index of the medium.

Light speed in various mediums
Speed ​​of medium light (m / s)
Vacuum 3.00 x 108
Water 2.25 × 108
Glass 2.00 x 108
Turpentine Oil 2.04 x 108
Nylon 1.96 × 108
It takes about 500 seconds or 8 minutes for sunlight to reach the Earth.

Solar eclipse: When the moon comes between the sun and the earth, the sunlight does not reach the earth. This condition is called solar eclipse. This can only happen on Amavasya.

Moon Eclipse: When the Earth comes between the Sun and the Moon, the light emanating from the Sun is not found on the Moon. Such a situation is called lunar eclipse. This can happen only on the full moon.

Reflection of Light

When the light falls on a smooth or bright surface, most of it returns in different directions. In this way, the incident of light coming back after hitting a page is called reflection of light. If the page is opaque, some part of it is absorbed. If it is transparent, some part crosses the surface.

Smooth and glossy polished surfaces reflect most of the light. A plane mirror is the best reflector of light. The reflection perpendicular to the straight line perpendicular to the surface and the ray which falls on the reflecting plane, is called the incident ray and the ray which returns back after reflection is called the reflected ray.

The angle between the incident ray and the normal is called the angle of incidence and the angle between the normal and reflected ray is called the reflection angle.

Reflection of light is based on two rules:

The incident ray, reflected ray and the normal are in the same plane.
The angle of incidence is equal to the angle of reflection.
An image of an object at a point from a plane mirror is formed at the same distance behind the mirror as the distance the object is placed in front of the mirror. This image is virtual and is equal to the object.

If a person walks towards the mirror at n speed, then he will see his image in the mirror coming towards him with 2n speed.
If the mirror is rotated at a q ° angle keeping the incident ray fixed, then the reflected ray rotates at a 2q ° angle.
If a person wants to see his full image in the mirror, then the minimum height of the mirror should be half of the height of the human.
The image is imaginary, straight and latterly reversed by a plane mirror.
Refraction of Light

When light passes from one medium to another, the phenomenon of deviating from its linear path at the boundary of another medium is called refraction of light.

When the ray of light enters the dense medium through the sparse medium, the beam turns from the surface of the dense medium towards the normal. When the beam enters the sparse medium through a dense medium, it moves away from the normal from the surface of the sparse medium. But the ray which perpendicularly enters into any medium, does not bow down on either side and exits directly.

The reason for refraction of light is the variation of velocity in different mediums.

Imported volume angle

The refractive index of a medium varies for the light of different colors. The value of refractive index decreases as the wavelength of light increases. Red color has the lowest refractive index and maximum of purple color in visible light, because the red wavelength is the highest and the purple color is the lowest.

The value of refractive index decreases with increasing temperature. In the refraction process, the speed, wavelength and intensity of light change but the frequency does not change. Due to refraction, any wood or spoon immersed in water looks crooked when seen from outside.

The shimmer of stars at night, the depth of the pond seems to be low, the sun is visible even below the horizon, etc. are due to refraction. When the virtual depth of an object in water is known, multiplying the refractive index of water in it, the actual depth is known.

Incidence of light refraction

The straight rod, partially submerged in the fluid, appears crooked due to refraction.
The stars are seen flickering due to refraction of light.
At sunrise, the sun is still below the horizon (ie before sunrise), it is still visible.
At sunset, the sun goes below the horizon, meaning that it is visible even when it has actually set. This is due to refraction of light.
A coin lying in the bottom of a vessel appears to be lifted up, it is also the result of refraction.
Full internal reflection

When the light penetrates through the sparse medium, the refracted ray moves away from the normal. As the value of incidence angle increases, the refracted ray moves away from the normal. A situation occurs when the value of angle of refraction for the angle of incidence becomes 90 °. A situation in which the refracted angle has a value of 90 ° is called the incident angle, the critical angle. When the incident angle is enlarged further than the critical angle, the beam again returns to the medium through which it moved. This phenomenon is called full internal reflection of light.

There are many examples of this, such as – the sparkling of diamonds, the appearance of Marichika in hot and cold regions, the excess shine of broken glass, the silver-filled test tube filled with water, shining like silver, etc.

Medical, transmission of optical signals, sending and receiving of electrical signals uses optical fiber, which works on the principle of full internal reflection, some examples of which are:

The test tube lying in the water looks bright.
The cracks in the glass glow.
A ball smeared with soot glows in water.

When a ray of light enters a sparse medium through a dense medium, it retreats away from the normal. The refractive angle increases as the incident angle increases. At a certain value of the incident angle, the refracted angle becomes a degree of 90 °. This value of incident angle is called critical angle. When the value of the incident angle exceeds the critical angle, light does not go into the sparse medium, but is reflected in the dense medium itself. This is called complete internal reflection of light. There are many examples in nature of complete internal reflection. In the desert and cold regions, the cause of marichika is also the complete internal reflection of light.

Desert girl

Generally, travelers traveling in the desert during the afternoon of summer get the illusion of having water at some distance. This confusion is called the mirage of the desert or Marichika.

The sandy land of the desert becomes hot due to heat. Therefore the warm layers of air near the earth are sparse, but they are relatively dense as the upper layers are cold.

In such a state, the rays of light coming from the top of an object or tree are refracted from the various addresses of the air and move away from the normal. A situation arises when the angle of incidence of these rays on a layer of air exceeds the critical angle for consecutive addresses. This causes complete internal reflection of these rays. Now these rays are reflected in the upper medium and reach the eyes of the passengers. In this way, travelers see an inverted reflection of the tree. Inverse reflection makes them feel as if there is water ahead.

The deer also has the same feeling in the desert and he loses his life by running for want of water.

Cold in cold regions

This scene is also seen in cold regions like desert. It is called Marichika of cold state. There is also a village on the southern side of Italy, where people often see an inverted city in the nearby island of Sicily. It is called Fata Morgana.

In cold regions, the air near the ground becomes colder and denser, but the upper layers are relatively warm. In this way, different layers of air move upwards from the ground. A ray coming from a ship or other object floating in a distant sea is refracted from different layers of air and moves away from the normal and comes to a state when the incidence angle on a layer of air exceeds the critical angle And there is complete reflection of light. Due to reflection, this ray is refracted from various addresses of the air and bends towards the normal, and we see a ship floating in the sea or a view of a far distance hanging in the sky. In such a marina, up to about 120 degrees around the horizon, mountains and snowy peaks etc. are seen vomiting.

There are other examples of complete internal reflection, such as the cutting of diamonds at different angles, causing full reflection to add shine to it.

Two things are necessary for full internal reflection of light from a prism of 90 ° degree –

The ray of light must pass through the dense medium into the sparse medium.
The value of incidence angle in the compact medium must be greater than the critical angle.

Image Image Formation

When an object is placed in front of a mirror, the light rays moving from the object are reflected from the bottom of the mirror and fall on the eye of the viewer, causing the viewer to see the shape of the object, this shape is called the reflection of the object.

The point where the light rays from a source meet after reflection or refraction from a plane is called the actual image of the point source and the point where the light rays appear to propagate after reflection or refraction is the virtual point of the source. It is called image. A virtual image cannot be taken on screen, while a real image can be taken on screen.

An image of an object made of a plane mirror is formed at the same distance behind the mirror as the distance the object is placed in front of the mirror. The image in the mirror has lateral reversal, that is, if the person standing in front of the mirror raises his left hand, his right hand will be seen in the image. To see the entire image of the object in the mirror, at least the length of the mirror should be half of the object. In front of a mirror, if a person moves near or away from a trick, he will find his image moving near or away with double speed.

If you place an object between two plane mirrors tilted at an angle, then many images of that object are seen. The number of images depends on the angle between the two mirrors.

If two plane mirrors are placed parallel to each other, then an angle of zero degree will be formed between them and infinite images of the object placed between the mirrors will be formed. Two plane mirrors are tilted at 60 ° under the polymorphism, showing many images of the object.

Spherical mirror

A hollow sphere has spherical surfaces. It is of two types – convex and concave mirror. The embossed plane, in which the polish is turned inward, the convex mirror and the other with the bottom pressed, the polish is on the outer surface, called the concave mirror. Reflection of light in a convex mirror is from the exposed outer surface and in a concave mirror the reflection is from a buried internal surface.

The midpoint of the reflective plane of a spherical mirror (convex or concave) is called the pole of the mirror.

The center of the sphere of which the mirror is part is called the curvature center of the mirror.

The line joining the mirror to the curvature of the pole is called the principal axis of the mirror.

The rays parallel to the main axis of the mirror, the point at which they meet or appear after reflection from the mirror, are called the main focus. The distance between the main focus and the dust is called the focus distance. The focus distance falls exactly between the pole and the main focus.

A convex mirror always makes a virtual, straight and small image.
A concave mirror will create a virtual, straight and large image.
Only when the object is placed between P (pole) and F (focus) in front of the mirror.

Mirror detection

There are two methods to identify mirrors:

By Touch: If the reflective plane is perfectly flat then the mirror plane, if the reflective plane has emerged in the middle, then the convex and if the reflective plane is pressed in the middle, then the mirror will be a concave mirror.

By looking at the image: If the image in the mirror gets smaller when the object is moved away from the mirror, the mirror will be convex, if the image of the object is straight and increases when the object is moved away, then the mirror will be concave and if the image If the shape is constant then the mirror will be a plane mirror.
Uses of Spherical Mirrors

Concave Mirrors: The rays coming from the Sun are reflected from the mirror at a focus distance, it is used in solar cookers to collect heat from the Sun as it can collect a large amount of heat. Large concave mirrors are used in reflective telescopes to do photography of celestial objects, stars etc.

It is also used to examine the inner parts of the ear, nose and throat because if an object is fixed near a concave mirror at a distance less than its focus, then the object is made upright, virtual and larger than the size of the object. is. The parabolic concave mirror is used in the searchlight and headlights of the motorcycles because the light rays emitting from the bulb adjacent to it are reflected in the mirror and converted into intensity rays.

Convex Mirrors: The image of an object in a convex mirror is virtual and smaller and perpendicular to the object. That is, in a convex mirror, the image of a very large area becomes a small area.

It is clear that the convex mirror has a greater field of vision. It is used in motor vehicles to view behind-the-scenes shots of the driver. It is also used in reflective lamps on the road because they spread light over a large area.

Surrounded by two planks, the two floors of which are transparent blocks of two spheres, are called lenses. They are used in all optical instruments such as cameras, projectors, telescopes and microscopes. They are made of glass (mainly 🙂 or plastic. There are two types of convex lenses and concave lenses.

Convex lens: The convex lens is thicker in the middle and thinner at the edges. The convex lens shrinks the rays coming from infinity, hence it is also called convergent. There are three types of convex lenses – biconvex, plane convex, concave lens.

Concave lens: It is thin in the middle and thick at the edges. A concave lens extends the rays coming from infinity, it is also called a divergent lens. There are also three types – ambient, plane, concave and convex lens.

The line connecting the curvature of both the plane of the lens is called the principal axis of the lens. The lenses have two focus and two curvature centers. The second focus of the lens is also called the main focus. In a convex lens the focus is real and concave lens is virtual. The focus distance of a convex lens is positive, and that of a concave lens is negative.

The point in the center of the lens is called the lens center. If the medium on both sides of the lens is the same, then both focus distances of the lens are equal.

Refraction of light by lens

A refractive medium surrounded by two spherical pages is called a lens. There are two types of lenses – Convex Lens and Concave Lens.

Lens capacity

In a convex lens, when the light rays are incident on the lens moving parallel to the principal axis, this lens after refraction bends those rays towards the principal axis and the concave lens removes these rays away from the principal axis.

Thus the function of the lens is to bend the rays incident on it. This is called the efficiency of the lens. The more the lens which bends the rays, the greater its capacity. The shorter focus distance lenses are more efficient and the longer focus distance lenses are less efficient.

The unit of lens capability is diopter. The capacity of a convex lens is positive, and that of a concave lens is negative. Their capabilities are added when two lenses are placed close together. When convex and concave lenses of equal focus distance are interconnected, they behave like flat glass. Their capacity is zero and the focus distance is infinite.


[latex] P = \ frac {1} {F} [/ latex] (will be in f / m)

When the lens is dipped in a fluid, both the focus distance and the efficiency of the lens change.

If a lens is immersed in a fluid whose refractive index is less than the refractive index of the lens, the lens’s focus distance increases and the efficiency decreases. But the nature of the lens remains unchanged.

If the lens is immersed in a fluid whose refractive index is equal to the refractive index of the lens, the focus distance of the lens is infinite and the potential is zero and the lens will behave like a flat plate and will not be visible.

If a lens is immersed in a fluid that has a refractive index greater than the refractive index of the lens, the nature of the lens will change. This is why the air bubble immersed in water (has a convex nature) behaves like a concave lens, because the refractive index of water is greater than air.

The capacity of a convex lens is positive.

The capacity of a concave lens is negative.

Character deflection of light

When sunlight passes through a prism, due to refraction, it is divided into light of different colors along with bending towards the base of the prism. The group of colors obtained in this way is called spectral and the process of dividing light into different colors is called character deflection.

Among the colors obtained from sunlight, purple color is at the bottom due to high deflection and red color is at the top due to low deflection. The order of different colors from bottom to top is purple, purple, blue, green, yellow, orange and red respectively.

In short, it is called Baijnihapinala. The wavelength of red color is the highest and the refractive index is the lowest and the velocity is also the highest. Violet light has the lowest wavelength and also low velocity because its refractive index is high. Wavelength of light is measured in angstram. As the refractive index of light colors increases in a substance, its speed in the medium decreases.


The reason for becoming an Indradhanush is reflection, full internal reflection and refraction. The rainbow always appears in the opposite direction of the sun and it appears in the morning in the west and in the evening in the east. Indra bow is of two types – primary and secondary.

The primary rainbow is formed when the sun rays incident on the drops are reflected twice and reflect once. It has red color on the outside and purple color on the inside.

A secondary rainbow is formed when the sun rays incident on the drops are twice refracted and reflected twice. The red color in it looks somewhat blurred towards the inside.


It is formed at the time of rains or after rains. It is formed due to color-deflection by small drops of water.
When the white rays of the sun fall on the water-drops, its light has full internal reflection from the concave plane within the droplet.
When it starts coming out of the drop it deflects and thus different colors appear.
Sometimes two rainbows appear. The second rainbow is formed in the droplets twice due to internal reflection.
They both have the same center and are in the opposite direction of the Sun.
When two rainbows are formed, one is called primary and the other is called secondary rainbow.
Scattering of light

When the sunlight passes through the atmosphere, the light is spread in different directions by the particles present in the atmosphere, this process is called scattering of light. Scattering of a color depends on its wavelength. The color of light whose wavelength is short, its scattering is high and the scattering of more wavelength is less.

In sunlight, the scattering is the lowest due to the violet color wavelength being the lowest and the scattering being the lowest because of the red wavelength. Due to the highest scattering of purple color, the sky appears blue. And because of scarcity of red color, the sun appears red while sinking and rising because other colors are dispersed.

Sea water also appears blue due to scattering. The sky appears black to astronauts from space because there is no scattering of light due to lack of atmosphere. The sky also appears black from the moon.

[latex] S = \ frac {1} {{\ lambda} ^ {4}} [/ latex]

S → Scattering

λ → wavelength

Color of goods

When light rays fall on objects, they reflect into the object and enter the eyes of the beholder and the object starts to appear. Objects reflect some part of the light and absorb some part. The reflected part of the light determines the color of the objects. Like- Rose leaves look green and red due to the petals reflecting red light. The remaining light is absorbed. If the rose is seen in green light then the leaves appear green and the petals are black. She reflects light of that color and absorbs the light of the remaining colors.

Mix of colors

Other colors can be obtained by mixing blue, red and green colors in the above mentioned quantities. These are called primary colors. These are used in color television. Yellow, Magenta, Peacock – Blue is called the secondary color. The two colors which combine to produce white light are called complementary colors.


The vital body part acts like a camera. The outer portion is covered with a hard opaque membrane called the shear. The embossed portion behind the cornea is called the cornea. (The cornea is extracted in the eye donation.) The back of the cornea is filled with a transparent fluid called Netrod.

The curtain iris behind the cornea controls the light entering the eye, which spreads in less light and shrinks in more light. That is why when entering a room with less light from outside, we see less for some time. The inverted, small and real image of the object is formed on the retina by the lens located behind the pupil.

The muscles in the eye keep increasing the curvature of the surface by putting pressure on the lens, which also reduces the focus distance. The acting panel absorbs light and the light is not reflected. The light rays moving through an object fall on the lens after passing through the cornea and the ophthalm, refracted from the lens and fall on the retina passing through the glassy fluid, forming an inverted and real image of the object on the retina.

The image of the image reaches the brain through the visual cells and the object is visible to the viewer.

There are two types of cells in the eye.

Cone Shaped → For Color
Rod Shaped → For light intensity
Eye sensitization

To see clearly it is necessary that the rays moving from the object are focused on the retina itself. The object will not be visible when the rays are focused back and forth. Slowly bring the object closer to the eye and keep the focus distance the same, then the rays moving from the object will begin to focus behind the retina and the object will not be visible.

As soon as the object is brought closer to the eye, the perivascular muscles adjust the lens so that the image of the object remains on the retina, reducing the focus distance of the lens. In this way, the property of adjusting the focus distance of the eye by the muscles of the eye is called the adjusting capacity of the eye.

The nearest distance in front of the eye, where the object is clearly visible to the eye, is called the minimum distance of clear vision of the eye. For a normal eye it is 25 cm. This is called the nearest point of the eye. Like a near point it is also a distant point, for a normal eye it is infinite. The human eye extends from 25 cm to infinity.

Vision defects and their prevention

Myopia: If the eye sees a nearby object but is unable to clearly see a distant object beyond a certain distance, then there is a defect of myopia in that eye. In this case, the image of a distant object does not form on the retina and is formed ahead of it.

Prevention: Concave lenses of suitable focus distance are used to correct myopia defects.

Distant vision: In this defect, the distant object is visible to the eye, but the object nearby is not visible clearly. The person has difficulty in reading the book.

Prevention: To correct this defect, a convergent (convex) lens is required to be used in the glasses.

Other vision defects

Visibility: In this, the eye cannot see the horizontal and vertical lines simultaneously clearly. To prevent this, cylindrical lenses are used. It is also called toric lens.
Varnadhata: The eye becomes sensitive to a particular color. The reason for this is that any cone of the retina becomes insensitive.
A little vision: Due to old age, neither near nor distant objects are seen. It is equipped with bifocal lens glasses.
Diffraction of light

The diffraction of light at the edges of barriers is called diffraction of light. The edges of the shadow of the barrier are not sharp due to diffraction. For this reason, the image of the stars in the telescope does not appear as sharp points and appears as obscure spots.

Diffraction of light depends on the size of the barrier. If the resistor is of the same wavelength of light, the diffraction is obvious, and if the barrier size is much larger than the wavelength of light, the diffraction will be negligible.

Diffraction confirms the wave nature of light. Sound waves are easily deflected by obstructions and reach the listener.

Interference of light waves

When two light waves of equal frequency and same amplitude are transmitted in the same direction from basically the same light source, the intensity of light at some points of the medium is found to be maximum and at some points the intensity is minimum.

This phenomenon is called interference of light waves. Interference at the points at which the intensity of light is maximum is called combinatorial interference and points at which the intensity is minimum is called destructive interference.

Light waves emanating from two independent sources do not cause interference. The colorful appearance of kerosene and soap bubbles spread on the surface of the water is an example of interference.

The energy of zero intensity places is not lost in the interpolation, the same energy is released at the places of maximum intensity.

Polarization of light waves

Light waves are a type of electromagnetic waves in which the electric and magnetic fields are perpendicular to each other and vibrate in perpendiculars to the direction of transmission of the waves. Electricity companies are mainly responsible for the transmission of light.

Since light waves are transverse waves, these electric vibrations are perpendicular to the direction of wave transmission. When these vibrations are distributed randomly in every direction located in the plane, then such waveform is called unfinished wave and if the electric vibration is not distributed uniformly in all directions in the plane in the same direction, then light waves are called polar waves. .

The film made of a mixture of nitro cellulose and herpethite is placed between two glass plates and is polarized by forming a polaroid. It is also used to avoid the glare of reflected light and to watch three-dimensional cinema.

Polaroid Uses

In sun glasses to remove the glare of light.
The windscreen of the motor car and the cover glass of the headlight are mounted on the polaroid. The axes of polaroids tilt at an angle of 45 ° from the vertical.
In controlling the intensity of light entering the aircraft and the train.
In viewing images with three dimensions.
In the study of the optical properties of metals.
In Polaroid Photography and Camera.
The camera

The actual image is obtained with the help of a convex lens in the camera. The camera is a metal anti-light box. The inner wall is blackened to absorb the incident ray. The lens in the front part and the last part consists of a thin layer of celluloid film coated with silver bromide and gelatin.

The gelatin curtain just behind the lens is called a diaphragm. The holes of the diaphragm can be enlarged or enlarged as necessary. The light (from 1/10 to 1/50 second) is applied to the film by opening the valve behind the lens. The film throws light on it, it is called Udbhasan Kaal.

It depends on the intensity of light. After washing the film in water, the washed film is poured into an aqueous solution of sodium thiosulfate (hypo). After washing and drying it, you get it negative, so that the real image is obtained on paper. White parts, black and black parts, white appear in the negative.

Viewing angle

The angle the object makes to the eye is called the viewing angle. The size of the object depends on it. When the angle of vision is large, the object will be big and small when it appears. The virtual size of the object can be increased by increasing the viewing angle through the visionary and microscope.

Simple microscope

This is such a device, with the help of which one can see subtle things. It has a convex lens of short focus distance. When an object is placed in front of the lens, less than its focus distance, a virtual, straight and large image of the object is seen.

It is used for viewing bacteria, checking for fingerprints and reading small scales. Electron microscopes are used to see superfluous particles, in which electrons are used instead of light rays. It shows the size of objects 5000 times larger than ordinary microscopes.

Joint microscope

Combined microscopes are used to obtain greater magnification capability than simple microscopes. It consists of two convex lenses. One is called the invisible and the other is called the nectar. The less focus distance lenses are used in the eye and the lens, the greater the magnification capacity of the microscope. It is used in observing microscopic flora and fauna and in checking blood and mucus.


It is used to see celestial bodies, moons, stars and other planets etc. It consists of two convex lenses one on the visual and the other on the eye. The visual lens is located on one side of a cylindrical tube and the ophthalmic lens is on the other side of the tube. Reflective telescopes are now being made with the difficulty of manufacturing large lenses, using concave mirrors as the reflective plane. Parabolic mirrors are also being used in some telescopes.

Astronomical telescope

The telescope was invented in 1608 by Hans Liparshi of Netherland. In 1909, the Galileans studied Jupiter’s moons and Saturn’s rings, making it the first successful telescope.

Astronomical telescope It is useful to see celestial bodies or objects located at extremely high distances. This device usually consists of two convex lenses, which are placed in a metal tube on the same common axis. The lens which is towards the object is invisible and the one which is towards the eye, it is called the eye.

The aperture of the astigmatism is larger and the focus distance is greater than that of the eyelet. A focusing knob is provided to change the distance between the two lenses. In this type of visionary, an inverted reflection of the object is formed. Prisms are used to straighten the reflection.

Reflective telescope

Newton invented the reflective telescope in 1668. This used curved mirrors instead of lenses. After this, N. Casigren developed other similar visionaries.

The reflector has a larger aperture in the reflecting telescope. There are no defects of chromatic aberration and spherical aberration. Reflective telescopes have very little absorption of light, so the reflection made from this is much clearer than in refractive telescopes.

The world’s largest reflecting telescope is the Gran Telescopio Canarias (GTC) in Spain. Whose mirror diameter is 10.4 m. is.

Radio telescope

They have a large metal antenna shaped like a dish, which can be rotated in any direction. It receives radio waves coming from celestial bodies. These radio waves go into the receiver. In this way information about stars and planets is obtained.

The largest telescope of this variety is located on a hill in the port of Arecibo, Puerto Rico. The diameter of its dish is 304. 80 m. is. It is capable of receiving radio waves coming from distances up to 1500 million light years.

A light year is the distance a light travels over a year. Its value is 9.46 x 1012 km. is. France also has one such powerful radio telescope.

Just a few years ago, scientists orbited the Hubble space telescope to orbit the Earth in space with the help of a space shuttle, which is ten times more powerful than any Earth telescope. The name of this telescope is Hubble Space Telescope.


In 1666, Newton poured sunlight through a prism through a hole in a window of a closed room, resulting in a strip of seven colors on the screen, with yellow at one end and violet at the other. Was. Seven colors were red, orange, yellow, green, blue, sky, and purple in this band respectively.

Newton called the spectrum a spectrum. These are represented in English by a word made of the first letters of these colors. With this experiment he proved that sunlight is actually a mixture of seven colors. It was only with this experiment that spectrum science started.

We see many examples of spectrum every day. The pieces of glass in the ceiling divide the white light into various colors like a prism. In the rainy season, rainbow is formed due to sunlight falling on innumerable water particles hanging in the sky.

The rainbow appears on the opposite side of the sun. It is made in the morning or evening only, not in the afternoon. Sometimes a double rainbow is also seen. In these, the order of the colors of the second rainbow is reversed.

After experimenting on the spectrum for a long time, it was found that even after the colors purple and red, there are colors, which cannot be seen with the eyes, but their effect can be easily seen on a photo film. These rays are called ultraviolet and infrared rays respectively.

Later many tests showed that there is more radiation than infrared and ultraviolet radiation. Now, based on theoretical calculations and experiments, it has become certain that all these waves, i.e. from gamma rays to radio waves, are part of the same family.

This family of them is called electromagnetic spectrum. Therefore, waves of different colors are divided on the basis of wavelength rather than color, because colors are arranged in the same order of wavelength.

The portion of visible light is much smaller than the entire electromagnetic spectrum, so this arrangement of characters according to wavelength is called spectrum.

Wavelength of light in different parts of visible light

Color wavelength in Å

Violet 3900– 4460
Blue 4460-4650
Sky 4650-5000
Green 5000-5700
Yellow 5700-5900
Orange 5900-6200
Red 6200-7600

Electromagnetic spectrum

Name in Wavelength (Angstram)

Gamma rays 103 Å to 0-01 Å
X rays 0–1Å to 100Å
Ultraviolet rays 100 Å to 4000Å
Visible light 4000Å to 8000Å
Infrared rays 8000Å to 107Å
Micro waves 107Å to 1011Å
Radio waves 1011 Å

Woleston made efforts to obtain pure spectrum. Fronhofer obtained a pure spectrum with the help of a prism and invented plane grating. Fronhofer’s work is of specific importance in the advancement of spectrum science. In 1860, Kirchhoff and Bunsen studied the spectrum of many elements and studied them.

He explained that the spectrum of each element has certain characteristics. When a substance is excited, it can absorb the same wavelengths it emits at low temperature.

There are two types of spectrum – emission spectrum and absorption spectrum.

Energy is given to the molecules or atoms of that object to obtain the emission spectrum of an object. Due to this external energy, molecules or atoms get excited and when they come to their original state from the excited state, the energy changes, consequently light starts coming out of them.

This light can be visible and invisible, two. If the wavelength of the emitted light is less than the wavelength of the purple color, an ultraviolet spectrum is formed. If the wavelength is longer than the red color wavelength, then an infrared spectrum is formed. Both of these are invisible radiation. The spectrum obtained from all glowing objects is called the emission spectrum.

If the spectrum emitted from an object is again passed through the vapor of the same object, it is absorbed by the vapor. If sodium vapors are filled in a tube and allowed to pass light from a source that produces a continuous spectrum, two black absorption lines are seen in the yellow part of the spectrum.

These lines are sodium lines. Taking the spectrum of the Sun by the spectrum, black lines appear everywhere in the spectrum. These are deciduous lines and were known by Fronhofer.

The emitted spectrum is also of two types – linear emitted spectrum and continuous emitted spectrum. The absorption spectrum is of three types – linear absorption spectrum, band spectrum and continuous absorption spectrum. Prism or Grotting spectrographs are used to study the spectrum. Now-a-days recording spectrographs are used, on which the spectrum is recorded on chart paper.

Solar spectrum and electromagnetic spectrum

The solar spectrum is called the emission spectrum of the sun. The spectrum consists of black multiple lines between continuous and bright lines. These black lines were first known by Colston in 1802. In 1815, Fronhofer rediscovered them and studied them.

These lines are called Fronhofer lines. Fronhofer named the lines on the basis of letters, but no conclusions could be drawn about their origin.

In 1860, Kirchhoff and Bunsen gave the reason for the origin of these lines. According to him, if the emitted lines of an object are again passed through the vapor of that object, then the lines emitted by the vapor are absorbed. It is also clear from this that the elements emitting these lines are present in the Sun.

About 20,000 Fronhofer lines have been known so far. It is known from the study of these lines. That there are about 36 elements present in the Sun, which are also found on Earth. There are some elements whose first existence was found in the sun itself.

The existence of the helium element was first known from the Sun and later Ramsey obtained it from Cleavite on Earth. We have learned many things about the internal structure of the Sun by studying Fronhofer lines.

The Sun is made up of gaseous substances, whose temperature is not the same everywhere. The temperature of the center is the highest and the outer is the lowest.

Lens capacity
Many optical instruments have multiple lenses. They are combined to make the image more magnified and clear. Thus the total capacitance of the lenses in contact is the algebraic sum of the individual capacitances of those lenses. like-

P = P1 + P2 + P3 + …….

For glasses makers, it is quite convenient to use the capabilities in place of the focus distance of the lenses. While testing the eyes, the goggler places the glasses inside the test frame, keeping in touch several different combinations of modifying lenses of known ability.

The glasses maker calculates the required lens capacity by simple algebraic sums. For example, the combination of two lenses with 2.0D and 0.25D capacities is equivalent to a single lens of + 2.25D capacity. This property of the compatibility of lens capabilities can be used to reduce some of the defects in reflections made by single lenses.

Lens bodies made by placing multiple lenses in contact with each other are commonly used in the design of cameras’ lenses and microscopes and visionaries.

By the color of light, we can tell the different colors in the sky by looking at the stars, whose temperature is low and whose temperature is high, such as light red star less hot, dark red star more hot, orange red star and more hot, yellow star than that. The warmer and the white star is the hottest.

Electromagnetic spectrum

Radio waves, infrared rays, ultraviolet rays, visible light, X-rays and gamma rays are all electromagnetic in nature. The range of infrared waves starts from a red colored edge to a wavelength of 4 × 102 cm. This is followed by the field of micro waves and radio waves.

Radiation of short wavelengths from visible light is called ultraviolet. Its range is 1 × 108 m. Wavelength. The area before it is called the area of ​​X rays. The area of ​​the x ray is 1 × 108 to 4 × 1012 m. Happens till then. Before this, the area of ​​gamma rays falls.

A fixed line cannot be drawn between any two areas, they are joined to each other. The cluster of all these fields is called the electromagnetic spectrum. In this group the field of visible light is very small.

Ultraviolet spectrum

Ritter discovered the ultraviolet spectrum in 1801. Some part of the Sun’s spectrum spreads under the purple part, which, while invisible to the eye, performs chemical activity. Its extension is 4 × 107 m. Wavelengths ranging from 1 × 108 m. Happens till.

These rays chemically act on photographic films. Due to the high temperature of the Sun, they are high in sunlight, but most of it is absorbed by atmospheric gases. In fact, these rays are highly energetic photons.

These rays are produced by artificial means and they are used to destroy germs of many diseases. These rays are also used in the treatment of many diseases. These rays produce fluorescence and phosphorescence in some substances.

Infrared spectrum

William Harschel discovered the infrared spectrum in 1800. Some part of the Sun’s spectrum is also spread over the red part, which is not visible to the eyes, but produces a thermal effect. Its expansion is 7.8 × 107 m. Wavelengths ranging from 1 × 103 m. Wavelength.

For the treatment of various types of pain, the body is compacted with these rays. They can be photographed in the dark without light. Everything from an infrared telescope can be seen at night, in the same way as these telescopes are used during war in airplanes and tanks in daylight.

What is vision defect

Damage to any part of the vision system or malfunctions can cause significant damage to vision functions. For example, any structure involved in light transmission (eg cornea, pupil, eye lens, ophthalmic and vitreous fluid) or retina-like structure (which are responsible for converting light into electrical signals), or visual nerve (which Carries these signals to the brain), even when damaged produces an aural deformity.

You must have realized that when you enter a dimly lit room with intense light, initially you are not able to see the objects of that room for some time.

However, after some time you can see the objects of the same dimly lit room. The pupil of the eye acts like a variable gasket, whose shape can be changed with the help of an iris. When the light is too bright, the iris shrinks and makes the pupil smaller, allowing less light to enter the eye.

But when the light is dim, the spiral makes the pupil larger, allowing more light to enter the eye. In this way, the pupil opens completely due to the laxity of the iris in dim light.

radio waves

Different radio waves are used for different tasks. The main use of these rays is being used in modern communication systems like radio, TV, telephone, fax etc. Some important radio waves are as follows-

Special time signals for VLF (Extremely Low Frequency) scientists.

LF (Low Frequency or Long Waves) radio signal and AM for ship communication. (Import modulated) for radio.

HF (High Frequency or Shortwave) in non-intrusive radio.

V.H.F. (Very high frequency) FM (frequency modulated) radio in black and white television.

For MF (Medium Frequency or Medium Wave) Police Radio and MF (Dimension Modulated) Radio.

UHF (Ultrahigh Frequency) in color television.

SHF (Super High Frequency) for space and communication satellites.

The entire electromagnetic spectrum is extremely useful to humans.

Fluorescence and phosphorescence

Fluorescence: There are some substances on which when some light is thrown, different types of light are emitted from them for a very short time. Such a substance is called fluorescent material and this activity is called fluorescence.

Fluorescence absorbs matter when a light of less wavelength, ie more energy, is applied. Some of the absorbed energy is emitted as heat and the remaining as light of longer wavelength. The energy of this emitted light is less than the light emitted.

Fluorescence nowadays has many practical uses, such as the tubelight used in homes. It is a long thick glass tube. Its walls are covered with magnesium, tungstate and beryllium silicate. Two tungsten metal electrodes are placed at both its ends.

After removing the air inside the tube, fill neon gas and put two to four drops of mercury in it. There is an immersion in the tube when given electricity. Ultraviolet rays emit mercury immersion. These rays are absorbed by the object on the glass wall and are again emitted as visible rays.

When ultraviolet rays are added to the acidic quinine solution, the solution begins to glow blue.

Sphuradipti: You may have noticed that even after the television is turned off, its screen keeps flashing for a long time. If the substance is brightened by any radiation and the substance remains glowing even after the radiation is stopped, then such substances are called phosphorescence substance and this action is called fluorescence.

This is because after absorbing the light, the molecules or atoms of the object return to their original state after being in the excited state for too long. The longer the molecule remains in the excited state, the substance keeps on glowing. Some objects are such that they glow until hours after the radiation ends.

Some special types of paints and paints contain phosphorescent substances, such as fluorescein, eosin, rhodamine and stillbine. They are used in advertisement boards and street signs.

Now they are also used in watches and electrical switches. These are coated with such substances, which absorb light in the day and shine in the darkness of night. Similarly, when calcium sulfide is brightened in ultraviolet light, it glows for a long time in a dark room. It is caused by phosphorescence.

Why do we have two eyes for sight, why not only one?

We have many benefits of having two eyes instead of one eye. This expands our field of vision. The horizontal field of vision of a human eye is about 150 degrees, while it goes about 180 degrees by two eyes. In fact, the capability of detecting the publication of a dimly lit object is increased by two detectors rather than one.

The two eyes of the prey animals are usually located in opposite directions on their head, so that they can get maximum wide field of view. But both our eyes are situated in front of the head. In this way our field of vision is reduced, but we get the benefit of stereoscopic eye.

Close one eye, you will find the world flat-only two-dimensional. Open both eyes, you will see the third dimension of depth in the objects of the world. Because there is a separation of a few centimeters between our eyes, each eye sees a slightly different reflection of an object.

Our brain makes a reflection by combining both reflections. In this way, using additional information, we tell how close or far an object is to us.

Tyndall Effect Tyndall Effect

Earth’s atmosphere is a heterogeneous mixture of microscopic particles. These particles include smoke, microscopic droplets of water, suspended particles of dust and air molecules. When a beam of light hits such fine particles, the path of that beam starts appearing.

The light diffused by these particles is reflected and reaches us. The phenomenon of scattering of light by colloid particles produces a Tyndall effect, when a thin light beam from a microscopic hole enters a room full of smoke, this phenomenon can be seen.

Thus, scattering of light makes particles visible. When sunlight passes through the canopy of a dense forest, the Tyndall effect develops.

The color of the scattering light depends on the size of the scattering particles. Extremely fine particles mainly scatter light below, while larger-sized particles scatter light of greater wavelength. If the scattering particles are very large, then the scattering light may also appear white.


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