Refraction and its Uses Done by: Andrew Ong

Content Uses of refraction in Optic fibres Telescopes Glasses Cameras Magnifying glass Plus: 1)Water-filled spheres, known an lacemakers' condensors 2) Schlieren Photography 3) Mirages

Refraction Refraction is defined as the bending of a light wave when it passes from one medium to another at the surface separating the two media. It basically occurs due to the speed of light being different in different media of different densities.

Refraction Refraction of light waves is governed by the two Laws of Refraction: The incident ray, refracted ray and the normal at the point of incidence lie in the same plane. The sine of the angle of incidence bears a constant ratio with the sine of the angle of refraction for a given pair of media. This is also known as Snells Law. n 1 sinθ 1 = n 2 sinθ 2

r >i r <i Ray of light bends towards the normal when it enters a denser medium at an angle Ray of light bends away from the normal when it enters a less dense medium at an angle Refraction

Optic Fibres The light in a fiber-optic cable travels through the core by constantly bouncing from the cladding using a principle called total internal reflection. Because the cladding does not absorb any light from the core, the light wave can travel great distances.

Optic Fibres The core is the inner part of the fiber, which guides light. The cladding surrounds the core completely. The refractive index of the core is higher than that of the cladding, so light in the core that strikes the boundary with the cladding at an angle shallower than critical angle will be reflected back into the core by total internal reflection.

Total Internal Reflection The core is optically more dense than the cladding. The light ray will undergo total internal reflection as it strikes the interface between the core and cladding as the incident ray has exceeded the critical angle.

Diagram on how refraction/ total internal reflection works Medium of higher refractive index Medium of lower refractive index normal Angle of refraction = 90º Critical angle i c Refracted beam Partially reflected beam Total Internal Reflection – Critical Angle

Total Internal Reflection Snells law: qcqc Water (n=1.3) Air (n=1.0)

Advantages of Fiber Optics Why are fiber-optic systems revolutionizing telecommunications? Compared to conventional metal wire (copper wire), optical fibers are: Less expensive - Several miles of optical cable can be made cheaper than equivalent lengths of copper wire. This saves your provider (cable TV, Internet) and you money. Thinner - Optical fibers can be drawn to smaller diameters than copper wire. Higher carrying capacity - Because optical fibers are thinner than copper wires, more fibers can be bundled into a given-diameter cable than copper wires. This allows more phone lines to go over the same cable or more channels to come through the cable into your cable TV box. Less signal degradation - The loss of signal in optical fiber is less than in copper wire. Light signals - Unlike electrical signals in copper wires, light signals from one fiber do not interfere with those of other fibers in the same cable. This means clearer phone conversations or TV reception.

Advantages of Fiber Optics Low power - Because signals in optical fibers degrade less, lower- power transmitters can be used instead of the high-voltage electrical transmitters needed for copper wires. Again, this saves your provider and you money. Digital signals - Optical fibers are ideally suited for carrying digital information, which is especially useful in computer networks. Non-flammable - Because no electricity is passed through optical fibers, there is no fire hazard. Lightweight - An optical cable weighs less than a comparable copper wire cable. Fiber-optic cables take up less space in the ground. Flexible - Because fiber optics are so flexible and can transmit and receive light, they are used in many flexible digital cameras for the following purposes:

Telescopes(or Refractors) Commonly known as refractors, telescopes of this kind are used to examine the visible-light region of the electromagnetic spectrum. Typical uses include viewing the Moon, other objects of the solar system such as Jupiter and Mars, and double stars. Usually used to view objects at a great distance away from the viewer. The name refractor is derived from the term refraction, which is the bending of light when it passes from one medium to another of different density.

Telescopes(or Refractors) The focus is the point, or plane, at which light rays from infinity converge after passing through a lens and traveling a distance of one focal length. In a refractor, the first lens through which light from a celestial object passes is called the objective lens. It should be noted that the light will be inverted at the focal plane. A second lens, referred to as the eyepiece lens(used to invert the image formed from the first lens), is placed behind the focal plane and enables the observer to view the magnified, upright image.

Telescopes(or Refractors) Hence, in a telescope, light from a very faraway object(which gives out parallel rays of light), is refracted and converged to a smaller focus at the eye. This results in a clear, upright and magnified image forming at the eye. Image seen will be upright, magnified and clear

Glasses(Eye refraction disorders) Myopia Those with myopia see near objects clearly but far away objects appear blurred. With myopia, the eyeball is too long, or the cornea is too steep, so images are focused before the retina, rather than on the retina at the back of the eye. Hyperopia The opposite defect of myopia is hyperopia or "farsightedness" or "long-sightedness"this is where the cornea is too flat or the eye is too small.

Glasses Corrective lenses are used to correct refractive errors of the eye by modifying the focal length of the lens in order to solve the effects of conditions such as: 1)nearsightedness (myopia), 2)farsightedness (hyperopia)

Diagrams of Myopia, Hyperopia Myopia Hyperopia

Vision(Eye) The process of vision begins when light rays that reflect off objects and travel through the eye's optical system are refracted and focused into a point of sharp focus. For good vision, this focus point must be on the retina. The retina is the tissue that lines the inside of the back of the eye, where light-sensitive cells capture images in much the same way that film in a camera does when exposed to light. These images then are transmitted through the eye's optic nerve to the brain for interpretation. The eye's pupil widens or constricts to control the amount of light that reaches the retina. In dark conditions, the pupil widens. In bright conditions, the pupil constricts.

Vision(Eye) When light travels through water or a lens, for example, its path is bent or refracted. Eye structures have refractive properties similar to water or lenses and can bend light rays into a precise point of focus(at the retina) essential for sharp vision. Most refraction in the eye occurs when light rays travel through the curved, clear front surface of the eye (cornea). The eye's natural (crystalline) lens also bends light rays. Even the eye's tear film and internal fluids (aqueous humor and vitreous) have refractive abilities.

Camera A camera's aperture (called the diaphragm) is used to adjust the amount of light needed to expose film in just the right way. The optical component of the camera is the lens. At its simplest, a lens is just a curved piece of glass or plastic. Its job is to take the beams of light bouncing off of an object and redirect them so they come together to form a real image -- an image that looks just like the scene in front of the lens.

Cameras Just like the eye, the camera lens has a different optical density than the surrounding environment. Hence, parallel light beams from a faraway object would converge at a single point, forming a diminished and inverted image. Hence, at the eyepiece, there is another piece of lens which causes the image to appear upright and magnified, which the human eyes picture.

Magnifying Glass A magnifying glass is a convex lens which is used to produce a magnified image of an object. A magnifying glass works by creating a magnified virtual image of an object behind the lens. The distance between the lens and the object must be shorter than the focal length of the lens for this to occur. Otherwise, the image appears smaller and inverted, and can be used to project images onto surfaces.

Magnifying Glass Diagram of Magnifying Glass

Lacemakers condensors The refraction of light can be used for various purposes. Water-filled spheres, known an lacemakers' condensors, were used in the early nineteenth century by lacemakers to help them see their work. Light passing through these condensors was bent and refracted in such a way, so that the rays meet and converge at a small and concentrated point and light up only a small area of the cloth to enable the lacemaker to focus on it.

Schlieren Photography(Apparent Depth) Schlieren Photography, which uses the fact that air at different temperatures bends light by different amounts. The refractive index of a particular substance which occurs in a huge quantity such as a water reservoir can also be used to measure its real depth by measuring the apparent depth. Since light coming from a denser medium such as glass or water is bent away from the normal, the depth at which an object inside that medium appears to be less than its real depth.

Schlieren Photography(Apparent Depth) An object seen in the water will usually appear to be at a different depth than it actually is, this is due to the refraction of light rays as they travel from the water into the air. Apparent depth

Schlieren Photography(Apparent Depth)

Mirage When light travels from a rarer medium to a denser one, it bends towards the normal. When it travels from a denser medium to a rarer one, it bends away from the normal. This bending of light has many implications, one of which is quite prominent in nature - mirage. A mirage occurs in very hot conditions, when a layer of warm air, next to the ground is trapped by the relatively cooler air above. Light is successively bent by these different layers of different densities towards the horizontal line of vision and eventually is made to travel upwards by total internal reflection at one of these layers. When these light rays reach the human eye, the human brain perceives them as coming from the image of the object, beneath it, thus giving the wrong impression of a pool of water at some distance. This phenomenon is most prominent on long roads on very hot days and in hot deserts.

Mirage Another type of mirage, called looming, occurs in extemely cold conditions, when a layer of relatively warm air, lies over another of cool air. The light rays travelling from the cold to the warm layer are bent away from the normal, and finally reflected downwards, to give an impression of an image looming above the real object.

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