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Use of light:
All animals, birds are able to see the objects around them due to presence of eyes. But without light these eyes might be absolutely of no us . Because of light, the eyes can receive the image of the objects and send the information to the brain. From this visual information we comprehend the objects. Hence we can notice that in darkness we could see nothing. So light makes us able to see objects around.

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Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum. The word usually refers to visible light, which is visible to the human eye and is responsible for the sense of sight.[1] Visible light is usually defined as havingwavelengths in the range of 400–700 nanometres (nm), or 4.00 × 10−7 to 7.00 × 10−7 m, between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths).[2][3] This wavelength means a frequency range of roughly 430–750terahertz (THz).

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| Light travels very, very fast. The speed of light in a vacuum (an area empty of matter) is around 186,000 miles per second (300,000 kilometres per second).Light travels slower through different mediums such as glass, water and air. These mediums are given a refractive index to describe by how much they slow the movement of light. Glass has a refractive index of 1.5, meaning that lights travels through it at around 124,000 miles per second (200,000 kilometres per second). The refractive index of water is 1.3 while the refractive index of air is 1.0003, meaning that air only slightly slows down light.Light takes 1.255 seconds to get from the Earth to the Moon.Sunlight can reach a depth of around 80 metres (262 feet) in the ocean.One of the many things Italian scientist Galileo Galilei worked on was telescopes, producing telescopes with around 30x magnification in some of his later work. These telescopes helped him discover the four largest moons orbiting Jupiter (later named the Galilean satellites).Photosynthesis is a process that involves plants using energy from sunlight to convert carbon dioxide into food.  |

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In physics, light refers to electromagnetic radiation. The light we normally talk about in everyday life refers to the visible spectrum (the part of the electromagnetic spectrum that the human eye can see).

Other animals can see parts of the spectrum that humans can’t. For example, a large number of insects can see ultraviolet (UV) light.

UV light can be used to show things the human eye can’t see, coming in handy for forensic scientists.

The wavelength of infrared light is too long to be visible to the human eye.

Scientists study the properties and behaviors of light in a branch of physics known as optics.

Isaac Newton observed that a thin beam of sunlight hitting a glass prism on an angle creates a band of visible colors that includes red, orange, yellow, green, blue, indigo and violet (ROYGBIV). This occurred because different colors travel through glass (and other mediums) at different speeds, causing them to refract at different angles and separate from each other.

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Refraction is the bending of a wave when it enters a medium where its speed is different. fraction occurs when light passes across the boundary between two media. Refraction is also one of the several possible boundary behavior which a light wave could behave when it encounters a new medium. Light refracts whenever it travels at an angle into a substance with a different refractive index. This change of direction is caused by a change in speed.

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Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum. The word usually refers to visible light, which is visible to the human eye and is responsible for the sense of sight.[1] Visible light is usually defined as having wavelengthsin the range of 400–700 nanometres (nm), or 4.00 × 10−7 to 7.00 × 10−7 m, between theinfrared (with longer wavelengths) and theultraviolet (with shorter wavelengths).[2][3]This wavelength means a frequency range of roughly 430–750 terahertz (THz). The main source of light on Earth is the Sun.Sunlight provides the energy that green plantsuse to create sugars mostly in the form of starches, which release energy into the living things that digest them. This process ofphotosynthesis provides virtually all the energy used by living things. Historically, another important source of light for humans has been fire, from ancient campfires to modern kerosene lamps. With the development of electric lights and power systems, electric lighting has effectively replaced firelight. Some species of animals generate their own light, a process calledbioluminescence. For example, fireflies use light to locate mates, and vampire squids use it to hide themselves from prey. The primary properties of visible light areintensity, propagation direction, frequency or wavelength spectrum, and polarization, while its speed in a vacuum, 299,792,458 metres per second, is one of the fundamentalconstants of nature. Visible light, as with all types of electromagnetic radiation (EMR), is experimentally found to always move at this speed in a vacuum.[citation needed] In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not.[4][5] In this sense,gamma rays, X-rays, microwaves and radio waves are also light. Like all types of light, visible light is emitted and absorbed in tiny "packets" called photons and exhibits properties of both waves and particles. This property is referred to as the wave–particle duality. The study of light, known as optics, is an important research area in modern physics.

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Light refers to electromagnetic radiation of any wavelength, whether visible or not. Light is electromagnetic radiation that has properties of waves. The electromagnetic spectrum can be divided into several bands based on the wavelength.The speed of light in a vacuum is defined to be exactly 299,792,458 m/s which is approximately 186,282 miles per second. Refraction is the bending of light as it passes through materials of different density.

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Sun is a natural light source which provides light for plants🌱  and vegetables for them to photosynthesis and provide us food and oxygen.It also reflect light to the moon.Refraction is the change of propagation of any wave as a result of its travelling at different points along the wave front.And sunlight🌞 carries energy which warm up the earth and is the driving force behind all our weather and climate.Without sunlight,we can't see things and the earth and moon will be in dark.

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Light travel in a straight line.Water can bend light.Light is needed for us to see.

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1) Sunlight can reach a depth of 80 metres in the ocean. Roughly 2000 metres deeper lives the bioluminescent anglerfish, which has a "lure" of glowing flesh to attract prey. Also it's hideout.
2) Plants are green because they reflect green light and absorb the other colours for photosynthesis. If you put a plant under green light, it will probably die.
3) The world longest-lasting light bulb, the centennial light in California, has reportedly been burning since 1901, with a few interruptions during power failures.

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The main source of light on Earth is the Sun.Sunlight provides the energy that green plantsuse to create sugars mostly in the form of starches, which release energy into the living things that digest them. This process ofphotosynthesis provides virtually all the energy used by living things. Historically, another important source of light for humans has been fire, from ancient campfires to modern kerosene lamps. With the development of electric lights and power systems, electric lighting has effectively replaced firelight. Some species of animals generate their own light, a process calledbioluminescence. For example, fireflies use light to locate mates, and vampire squids use it to hide themselves from prey.

Light is genrally important in our daily lives🌍🔥

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Light is all around us. It is the primary way we come to know the universe, and thus is very important to physicists. Until the middle of 1800’s, light was taken to be a stream of tiny particles. This was the stance advocated by Newton. However, by the late 1800’s the particle theory was replaced by the wave theory. This was because light exhibited certain properties that could only be explained by the wave theory. One of the properties of light is that it reflects off surfaces. Among other things, this reflection allows us to see images in mirrors. We see the images in mirrors as apparently coming from behind the mirror because our eyes interpret it in this manner. But when we see ourselves reflected in the mirror and raise our left arm, the image apparently raises its right arm. Another property is the speed of light, which is the fastest anything has been observed to move. In a vacuum, the speed is 300 million meters per second. At that speed, it takes light one ten thousandth of a second to travel around the earth. When light enters a material, it slows down. The amount depends on the material it enters and it’s density. For example, light travels about 30% slower in water than it does in a vacuum, while in diamonds, which is about the most dense material, it travels at about half the speed it does in a vacuum. This slowing down of light plays a role in another property, refraction. Refraction means that light bends when it passes from one medium to another. When light enters a denser medium from one that is less dense, it bends toward a line normal to the boundary between the two media. The greater the density difference between the two media, the more the light bends. This property is used with respect to optical devices such as microscopes, corrective lenses for vision, magnifying lenses, and so on. You may have noticed that, when you look into the surface of a lake or pond while fishing, the fish you catch seems larger when under the water than when you actually land it. This is due to refraction. Since the air is less dense than water, the light beds away from the normal as it emerges. Another common example is that your feel look larger and closer to the surface underwater than they really are. Another property that combines both refraction and reflection is total internal reflection. This is an interesting concept. When light coming from the air strikes water, part is reflected and part is refracted. When the angle of incidence of the light striking the water is large enough, it gets totally reflected and in fact cannot leave the water. Fiber optics uses this property of light to keep light beams focused without significant loss, as long as the bending of the cable is not too sharp. TV and telephone cables use fiber optic cable more and more since it is much faster and more efficient than electrons in an electric current. Dispersion is another property of light. This refers to the ability to break white light into its constituent colors. White light consists of all of the colors we are able to see. If white light enters a prism, what emerges from the other side is a spread out beam of multi-colored light. Blue light, with longer wavelengths, gets bent more by the different angles of the prism than red light, and the other colors are in between blue and red on the wave spectrum. Rainbows are natural phenomena that exemplify all of the above properties of light. They use refraction, dispersion, and internal reflection to produce their amazing hues. White light enters raindrops from the sun and gets dispersed and refracted inside the raindrops. When the dispersed light hits the back of the raindrop, it gets internally reflected, and when it emerges it gets dispersed even more. Because it refracts more, the blue is always sat the top of the rainbow and the red on the bottom. The color you see most vividly depends on the angle of your eye. Generally, you must look higher in the sky to see the red, and lower to see the blue. What you actually see is the red on the top and the blue on the bottom, with all of the other colors in between. The arc of the rainbow depends on the angle that your line of sight makes relative to the sun behind you. Diffraction is yet another property of light. This term refers to the fact that light bends as it goes through an opening. While it is hard to give an everyday example of this, the closest would be when there is a light source shielded by a door such that only a limited amount of light can get through the opening. However, even the area shielded is a little brighter, reflecting some actual reflection and diffraction as well. An easier example is with another wave form, sound. When someone speaks from in front of an open door, a person standing way around the corner from the door will still hear the diffracted sound waves. Interference is another property of light. It is a phenomenon that occurs when two beams of light meet. Depending on both the nature of the two beams and when they meet, they can either merge and enhance one another and give a brighter beam, or they might interfere in such a way as to make the merged beam less bright. The former is called constructive interference, and the latter is destructive interference. It is not all that usual for us to encounter light interference in our everyday lives. One situation that is illustrative is where there is oil or gasoline floating on the surface of a puddle. Sometimes, you will see a brilliant pattern of colors given off by the oil or gas, even when the gas or oil is subjected to white light. What happens is that different potions of the film cause different colors in the white light to interfere constructively or destructively, depending on the thickness of the film. One region of the film might look red because the red light bouncing off the top of the film interferes constructively with red light passing through the film and is then reflected back off the water below it. We can see this more clearly with sound. When you are in the back of an auditorium, sound can reach you in a great may ways. It can take a direct path, be reflected off a ceiling, or walls, or the floor. All of these will reach you at slightly different times, and sometimes not at all. They can actually cancel each other out and you hear nothing when you sit in one area (a so called dead zone), and sitting in another, you can hear an abnormally loud sound. These are examples of destructive and constructive interference and the reason that modern auditoriums use sound absorbing materials on ceilings, walls and floors. One experiment used to demonstrate how light signals can interfere with one another is called “Young’s double slit experiment” after the physicist who used it for demonstrating the interference phenomenon. He set up a screen with two small slits and behind it set up another screen some distance away. When he subjected the first screen to a single light source, he found that there were alternate light and dark spots on the distance screen, corresponding to points where light rays coming from the two different slits underwent constructive and destructive interference. The light rays did not interact with one another in that one ray did not exert a force on the other. This is only possible when we think of light in terms of waves. So, what you “see” as you look out over your favorite landscape is a combination of light being reflected, refracted, dispersed, internally reflected, and diffracted. The computer inside your head (your brain) interprets all of the signals it receives from your eyes and makes a “picture” that we interpret as “seeing” that landscape. When they say beauty is in the eye of the beholder, it is really true. 

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Light is all around us. It is the primary way we come to know the universe, and thus is very important to physicists. Until the middle of 1800’s, light was taken to be a stream of tiny particles. This was the stance advocated by Newton. However, by the late 1800’s the particle theory was replaced by the wave theory. This was because light exhibited certain properties that could only be explained by the wave theory. One of the properties of light is that it reflects off surfaces. Among other things, this reflection allows us to see images in mirrors. We see the images in mirrors as apparently coming from behind the mirror because our eyes interpret it in this manner. But when we see ourselves reflected in the mirror and raise our left arm, the image apparently raises its right arm. Another property is the speed of light, which is the fastest anything has been observed to move. In a vacuum, the speed is 300 million meters per second. At that speed, it takes light one ten thousandth of a second to travel around the earth. When light enters a material, it slows down. The amount depends on the material it enters and it’s density. For example, light travels about 30% slower in water than it does in a vacuum, while in diamonds, which is about the most dense material, it travels at about half the speed it does in a vacuum. This slowing down of light plays a role in another property, refraction. Refraction means that light bends when it passes from one medium to another. When light enters a denser medium from one that is less dense, it bends toward a line normal to the boundary between the two media. The greater the density difference between the two media, the more the light bends. This property is used with respect to optical devices such as microscopes, corrective lenses for vision, magnifying lenses, and so on. You may have noticed that, when you look into the surface of a lake or pond while fishing, the fish you catch seems larger when under the water than when you actually land it. This is due to refraction. Since the air is less dense than water, the light beds away from the normal as it emerges. Another common example is that your feel look larger and closer to the surface underwater than they really are. Another property that combines both refraction and reflection is total internal reflection. This is an interesting concept. When light coming from the air strikes water, part is reflected and part is refracted. When the angle of incidence of the light striking the water is large enough, it gets totally reflected and in fact cannot leave the water. Fiber optics uses this property of light to keep light beams focused without significant loss, as long as the bending of the cable is not too sharp. TV and telephone cables use fiber optic cable more and more since it is much faster and more efficient than electrons in an electric current. Dispersion is another property of light. This refers to the ability to break white light into its constituent colors. White light consists of all of the colors we are able to see. If white light enters a prism, what emerges from the other side is a spread out beam of multi-colored light. Blue light, with longer wavelengths, gets bent more by the different angles of the prism than red light, and the other colors are in between blue and red on the wave spectrum. Rainbows are natural phenomena that exemplify all of the above properties of light. They use refraction, dispersion, and internal reflection to produce their amazing hues. White light enters raindrops from the sun and gets dispersed and refracted inside the raindrops. When the dispersed light hits the back of the raindrop, it gets internally reflected, and when it emerges it gets dispersed even more. Because it refracts more, the blue is always sat the top of the rainbow and the red on the bottom. The color you see most vividly depends on the angle of your eye. Generally, you must look higher in the sky to see the red, and lower to see the blue. What you actually see is the red on the top and the blue on the bottom, with all of the other colors in between. The arc of the rainbow depends on the angle that your line of sight makes relative to the sun behind you. Diffraction is yet another property of light. This term refers to the fact that light bends as it goes through an opening. While it is hard to give an everyday example of this, the closest would be when there is a light source shielded by a door such that only a limited amount of light can get through the opening. However, even the area shielded is a little brighter, reflecting some actual reflection and diffraction as well. An easier example is with another wave form, sound. When someone speaks from in front of an open door, a person standing way around the corner from the door will still hear the diffracted sound waves. Interference is another property of light. It is a phenomenon that occurs when two beams of light meet. Depending on both the nature of the two beams and when they meet, they can either merge and enhance one another and give a brighter beam, or they might interfere in such a way as to make the merged beam less bright. The former is called constructive interference, and the latter is destructive interference. It is not all that usual for us to encounter light interference in our everyday lives. One situation that is illustrative is where there is oil or gasoline floating on the surface of a puddle. Sometimes, you will see a brilliant pattern of colors given off by the oil or gas, even when the gas or oil is subjected to white light. What happens is that different potions of the film cause different colors in the white light to interfere constructively or destructively, depending on the thickness of the film. One region of the film might look red because the red light bouncing off the top of the film interferes constructively with red light passing through the film and is then reflected back off the water below it. We can see this more clearly with sound. When you are in the back of an auditorium, sound can reach you in a great may ways. It can take a direct path, be reflected off a ceiling, or walls, or the floor. All of these will reach you at slightly different times, and sometimes not at all. They can actually cancel each other out and you hear nothing when you sit in one area (a so called dead zone), and sitting in another, you can hear an abnormally loud sound. These are examples of destructive and constructive interference and the reason that modern auditoriums use sound absorbing materials on ceilings, walls and floors. One experiment used to demonstrate how light signals can interfere with one another is called “Young’s double slit experiment” after the physicist who used it for demonstrating the interference phenomenon. He set up a screen with two small slits and behind it set up another screen some distance away. When he subjected the first screen to a single light source, he found that there were alternate light and dark spots on the distance screen, corresponding to points where light rays coming from the two different slits underwent constructive and destructive interference. The light rays did not interact with one another in that one ray did not exert a force on the other. This is only possible when we think of light in terms of waves. So, what you “see” as you look out over your favorite landscape is a combination of light being reflected, refracted, dispersed, internally reflected, and diffracted. The computer inside your head (your brain) interprets all of the signals it receives from your eyes and makes a “picture” that we interpret as “seeing” that landscape. When they say beauty is in the eye of the beholder, it is really true. 

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Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum. The word usually refers to visible light, which is visible to the human eye and is responsible for the sense of sight.The main source of light on Earth is the Sun.Sunlight provides the energy that green plantsuse to create sugars mostly in the form of starches, which release energy into the living things that digest them. This process ofphotosynthesis provides virtually all the energy used by living things. Historically, another important source of light for humans has been fire, from ancient campfires to modern kerosene lamps. With the development of electric lights and power systems, electric lighting has effectively replaced firelight. Some species of animals generate their own light, a process called bioluminescence. For example, fireflies use light to locate mates, and vampire squids use it to hide themselves from prey.In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not.[4][5] In this sense,gamma rays, X-rays, microwaves and radio waves are also light. Like all types of light, visible light is emitted and absorbed in tiny "packets" called photons and exhibits properties of both waves and particles. This property is referred to as the wave–particle duality. The study of light, known as optics, is an important research area in modern physics.

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The study of light and the interaction of light andmatter is termed optics. The observation and study of optical phenomena such as rainbows and theaurora borealis offer many clues as to the nature of light.

Refraction

Main article: Refraction

An example of refraction of light. The straw appears bent, because of refraction of light as it enters liquid from air.

A cloud illuminated by sunlight

Refraction is the bending of light rays when passing through a surface between one transparent material and another.

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Mr Ong

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                                                Welcome!

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                                                Welcome!

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Please contribute to the class Padlet discussion on Light! Your discussion can focus on one or more of the following areas:

1) Properties of light (e.g. light travels in a straight line)

2) Light as a wave (e.g. electromagnetic spectrum, wavelength, frequency)

3) Uses of light around us (e.g. colour, lasers)

4) Reflection of light and its applications (e.g. mirrors, periscopes, interior design, optical fibres in fibre optic internet, one-way mirrors, curved mirrors)

5) Refraction of light and its applications (why is light refracted, optical illusions involving refraction, concave and convex lens, lenses in our eyes)
6) Any other issue related to light (e.g. how our eyes detect images, light in defence systems)