ECED 7 | Science, Health and Nature Study
Merylou M. Castellvi Prof. Josseme Tendido-Castro
ECED 7 | Science, Health and Nature Study
through small pores in the latex which are larger than the helium atoms. Ballo...
ECED 7 | Science, Health and Nature Study
For decades, people have also celebrated with balloon releases. This practice ...
ECED 7 | Science, Health and Nature Study
Flying machines
Large balloons filled with hot air or buoyant gas (often hydro...
ECED 7 | Science, Health and Nature Study
pressure inside would expand based on the high amount of internal forces, and ...
ECED 7 | Science, Health and Nature Study
Three major groups of rocks are defined: igneous, sedimentary, and metamorphic...
ECED 7 | Science, Health and Nature Study
Volcanic or extrusive rocks result from magma reaching the surface either
as l...
ECED 7 | Science, Health and Nature Study
mineral types or else into other forms of the same minerals, such as by recrys...
ECED 7 | Science, Health and Nature Study
Mining of stone and metal has been done since pre-historic times. Modern minin...
ECED 7 | Science, Health and Nature Study
India. Mirrors of speculum metal or any precious metal were hard to produce a...
ECED 7 | Science, Health and Nature Study
A low aluminium glass mirror is manufactured by coating silver and two layers...
ECED 7 | Science, Health and Nature Study
In a convex mirror, parallel beams become divergent, with the rays appearing ...
ECED 7 | Science, Health and Nature Study
rear-view sunglasses, the left end of the left glass and the right end of the...
ECED 7 | Science, Health and Nature Study
Atomic mirrors are devices which reflect matter waves. Usually, atomic mirror...
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  1. 1. ECED 7 | Science, Health and Nature Study 1 Merylou M. Castellvi Prof. Josseme Tendido-Castro BEEd 3A SCIENCE MATERIALS AND EQUIPMENTS INSIDE THE PRESCHOOL CLASSROOM Objectives: At the end of the lesson, the student will be able to: Introduce different materials and equipments inside the preschool classroom Demonstrate the different uses of science equipments Subject Matter: Topic: Science Materials and Equipments inside the Preschool Classroom Reference: Materials: visual aids, handouts, science materials Lesson Content: 1. Balloons A balloon is a flexible bag which can be inflated with a gas, such as helium, hydrogen, nitrous oxide, oxygen, or air. Modern balloons are made from materials such as rubber, latex, polychloroprene, or a nylon fabric, while some early balloons were made of dried animal bladders, such as the pig bladder. Some balloons are used for decorative purposes, while others are used for practical purposes such as meteorology, medical treatment, military defense, or transportation. A balloon's properties, including its low density and low cost, have led to a wide range of applications. The rubber balloon was invented by Michael Faraday in 1824, during the course of experiments with various gases. Party balloons are mostly made of a natural latex tapped from rubber trees, and can be filled with air, helium, water, or any other suitable liquid or gas. The rubber's elasticity makes the volume adjustable. As shown in the photo to the right, they can come in different colors like the rainbow such as red, orange, yellow, green, blue, purple, etc. Filling the balloon with air can be done with the mouth, a manual or electric inflater (such as a hand pump), or with a source of compressed gas. When rubber or plastic balloons are filled with helium so that they float, they typically retain their buoyancy for only a day or so, sometimes longer. The enclosed helium atoms escape
  2. 2. ECED 7 | Science, Health and Nature Study 2 through small pores in the latex which are larger than the helium atoms. Balloons filled with air usually hold their size and shape much longer, sometimes for up to a week. Even a perfect rubber balloon eventually loses gas to the outside. The process by which a substance or solute migrates from a region of high concentration, through a barrier or membrane, to a region of lower concentration is called diffusion. The inside of balloons can be treated with a special gel (for instance, the polymer solution sold under the "Hi Float" brand) which coats the inside of the balloon to reduce the helium leakage, thus increasing float time to a week or longer. Beginning in the late 1970s, some more expensive (and longer-lasting) foil balloons made of thin, unstretchable, less permeablemetallised films such as Mylar (BoPET) started being produced. These balloons have attractive shiny reflective surfaces and are often printed with color pictures and patterns for gifts and parties. The most important attribute of metalized nylon for balloons is its light weight, increasing buoyancy and its ability to keep the helium gas from escaping for several weeks. Foil balloons have been criticized for interfering with power lines Balloon modeling and balloons in art Balloon artists are entertainers who twist and tie inflated tubular balloons into sculptures (see balloon modeling). The balloons used for sculpture are made of extra-stretchy rubber so that they can be twisted and tied without bursting. Since the pressure required inflating a balloon is inversely proportional to the diameter of the balloon these tiny tubular balloons are extremely hard to inflate initially. A pump is usually used to inflate these balloons. Decorators may use helium balloons to create balloon sculptures. Usually the round shape of the balloon restricts these to simple arches or walls, but on occasion more ambitious "sculptures" have been attempted. It is also common to use balloons as table decorations for celebratory events. Balloons can sometimes be modeled to form shapes of animals. Table decorations normally appear with three or five balloons on each bouquet. Ribbon is curled and added with a weight to keep the balloons from floating away. Balloon drops and releases A decorative use for balloons is in balloon drops. In a balloon drop, a plastic bag or net filled with air-inflated balloons is suspended from a fixed height. Once released, the balloons fall onto their target area below. Balloon drops are commonly performed at New Year's Eve celebrations and at political rallies and conventions, but may also be performed at celebrations, including graduations and weddings.
  3. 3. ECED 7 | Science, Health and Nature Study 3 For decades, people have also celebrated with balloon releases. This practice has been discouraged by the balloon industry, as it has posed problematic for the environment and cities. In recent years, legislation, such as the California Balloon Law, has been enacted to enforce consumers and retailers to tether helium-filled foil (BoPET) balloons with a balloon weight. This ensures that the helium-filled balloons do not float into the atmosphere, which is both potentially injurious to animals, the environment, and power lines. Many states now have banned balloon releases, and organizations such as Balloons Blow have been created to educate people about the environmental issues At many events, the balloons may contain prizes, and party-goers can pop the balloons to retrieve the items inside. Balloon publicity Balloons are used for publicity at major events. Screen printing processes can be used to print designs and company logos onto the balloons. In January 2008, the Jewish Community Relations Council of New York organized a display of 4,200 red balloons outside the United Nations Headquarters Also in the 1950s at the start of the Cold War, activists in Western Europe uses balloons for propaganda purposes that would float east over Eastern Europe, which would release newspapers and pamphlets. Today, South Korean activists are using the same balloon method to get information to those in North Korea. Water balloons Water balloons are thin, small rubber balloons filled with a liquid, usually water, instead of a gas, and intended to be easily broken. They are usually used by children, who throw them at each other, trying to get each other wet, as a game, competition, or practical joke. By forcing water out the open end of a water balloon, it is possible to use it as a makeshift water gun. Balloon rockets Balloons are often deliberately released, creating a so-called balloon rocket or rocket balloon. Rocket balloons work because the elastic balloons contract on the air within them, and so when the mouth of the balloon is left open, the gas within the balloon shoots out, and, due to Newton's third law of motion, the balloon is propelled forward. This is the same way that a rocket works.
  4. 4. ECED 7 | Science, Health and Nature Study 4 Flying machines Large balloons filled with hot air or buoyant gas (often hydrogen or helium) have been used as flying machines since the 18th century. The earliest flights were made with hot air balloons using air heated with a flame, or hydrogen; later, helium was used. Unlike an airship, a balloon travels with the wind. Medicine Angioplasty is a surgical procedure in which very small balloons are inserted into blocked or partially blocked blood vessels near the heart. Once in place, the balloon is inflated to clear or compress arterial plaque, and to stretch the walls of the vessel, thus preventing myocardial. A small stent can be inserted at the angioplasty site to keep the vessel open after the balloon's removal. Balloon catheters are catheters that have balloons at their tip to keep them from slipping out. For example, the balloon of a Foley catheter is inflated when the catheter is inserted into the urinary bladder and secures its position. Insertion of balloons subsequently filled with air or liquid can be used to stop bleeding in hollow internal organs such as stomach or uterus. Air pressure Once inflated with regular, atmospheric air, the air inside the balloon will have a greater air pressure than the original atmospheric air pressure. Air pressure, technically, is a measurement of the amount of collisions against a surface at any time. In the case of balloon, it's supposed to measure how many particles at any in any given time space collide with the wall of the balloon and bounce off. However, since this is near impossible to measure, air pressure seems to be easier described as density. The similarity comes from the idea that when there are more molecules in the same space, more of them will be heading towards a collision course with the wall. The first concept of air pressure within a balloon that is necessary to know is that air pressures "try" to even out. With all the bouncing against the balloon wall (both interior and exterior) there will be a certain amount of expansion/contraction. As air pressure itself is a description of the total forces against an object, each of these forces, on the outside of the balloon, causes the balloon to contract a tiny bit, while the inside forces cause the balloon to expand. With this knowledge, one would immediately assume that a balloon with high air
  5. 5. ECED 7 | Science, Health and Nature Study 5 pressure inside would expand based on the high amount of internal forces, and vice versa. This would make the inside and outside air pressures equal. However, balloons have a certain elasticity to them that needs to be taken into account. The act of stretching a balloon fills it with potential energy. When it is released, the potential energy is turned into kinetic energy and the balloon snaps back into its original position, though perhaps a little stretched out. When a balloon is filled with air, the balloon is being stretched. While the balloon is constantly releasing kinetic energy in an attempt to contract, it is also being pushed back out by the constant bouncing of the internal air molecules. The internal air has to exert force not only to counteract the external air to keep the air pressures "even", but it also has to counteract the natural contraction of the balloon. Therefore, it requires more air pressure (or force) than the air outside the balloon wall. Two-balloon experiment The two-balloon experiment is a simple experiment involving interconnected balloons. It is used in physics classes as a demonstration of elasticity. Two identical balloons are inflated to different diameters and connected by means of a tube. The flow of air through the tube is controlled by a valve or clamp. The clamp is then released, allowing air to flow between the balloons. For many starting conditions, the smaller balloon then gets smaller and the balloon with the larger diameter inflates even more. This result is surprising, since most people assume that the two balloons will have equal sizes after exchanging air. The behavior of the balloons in the two-balloon experiment was first explained theoretically by David Merritt and Fred Weinhaus in 1978. 2. Rocks In geology, a rock is a naturally occurring solid aggregate of one or more minerals or mineraloids. For example, the common rock, granite, is a combination of the quartz, feldspar and biotite minerals. The Earth's outer solid layer, the lithosphere, is made of rock. Rocks have been used by mankind throughout history. From the Stone Age rocks have been used for tools. The minerals and metals we find in rocks have been essential to human civilization.
  6. 6. ECED 7 | Science, Health and Nature Study 6 Three major groups of rocks are defined: igneous, sedimentary, and metamorphic. The scientific study of rocks is called petrology, which is an essential component of geology. Classification of Rocks At a granular level, rocks are composed of grains of minerals, which, in turn, are homogeneous solids formed from a chemical compoundthat is arranged in an orderly manner. The aggregate minerals forming the rock are held together by chemical bonds. The types and abundance of minerals in a rock are determined by the manner in which the rock was formed. Many rocks contain silica (SiO2); a compound of silicon and oxygen that forms 74.3% of the Earth's crust. This material forms crystals with other compounds in the rock. The proportion of silica in rocks and minerals is a major factor in determining their name and properties Rocks are geologically classified according to characteristics such as mineral and chemical composition, permeability, the texture of the constituent particles, and particle size. These physical properties are the end result of the processes that formed the rocks. Over the course of time, rocks can transform from one type into another, as described by the geological model called the rock cycle. These events produce three general classes of rock: igneous, sedimentary, and metamorphic. The three classes of rocks are subdivided into many groups. However, there are no hard and fast boundaries between allied rocks. By increase or decrease in the proportions of their constituent minerals they pass by every gradation into one another, the distinctive structures also of one kind of rock may often be traced gradually merging into those of another. Hence the definitions adopted in establishing rock nomenclature merely correspond to more or less arbitrary selected points in a continuously graduated series. a. Igneous rocks Igneous rock (derived from the Latin word igneus meaning of fire, from ignis meaning fire) forms through the cooling and solidification ofmagma or lava. This magma can be derived from partial melts of pre-existing rocks in either a planet's mantle or crust. Typically, the melting of rocks is caused by one or more of three processes: an increase in temperature, a decrease in pressure, or a change in composition. Igneous rocks are divided into two main categories: plutonic rock and volcanic. Plutonic or intrusive rocks result when magma cools andcrystallizes slowly within the Earth's crust. A common example of this type is granite.
  7. 7. ECED 7 | Science, Health and Nature Study 7 Volcanic or extrusive rocks result from magma reaching the surface either as lava or fragmental ejecta, forming minerals such as pumice or basalt. The chemical abundance and the rate of cooling of magma typically forms a sequence known as Bowen's reaction series, after the Canadian petrologist Norman L. Bowen. Most major igneous rocks are found along this scale. About 64.7% of the Earth's crust by volume consists of igneous rocks; making it the most plentiful category. Of these, 66% are basalts and gabbros, 16% are granite, and 17% granodiorites and diorites. Only 0.6% are syenites and 0.3% peridotites and dunites. The oceanic crust is 99% basalt, which is an igneous rock of mafic composition. Granites and similar rocks, known as meta-granitoids, form much of the continental crust. Over 700 types of igneous rocks have been described, most of them having formed beneath the surface of Earth's crust. These have diverse properties, depending on their composition and how they were formed. b. Sedimentary rocks Sedimentary rocks are formed by sedimentation of particles at or near the Earth's surface and within bodies of water. This process causes clastic sediments or organic particles (detritus) to settle and accumulate, or for minerals to chemically precipitate (evaporite) from a solution. The particulate matter then undergoes compaction and cementation during diagenesis. Before being deposited, sediment was formed by weathering and erosion in a source area, and then transported to the place of deposition by water, wind, ice, mass movement or glaciers which are called agents of denudation. Mud rocks comprise 65% (mudstone,shale and siltstone); sandstones 20 to 25% and carbonate rocks 10 to 15% (limestone and dolostone).[3] About 7.9% of the crust by volume is composed of sedimentary rocks, with 82% of those being shales, while the remainder consists of limestone (6%), sandstone and arkoses (12%). c. Metamorphic rocks Metamorphic rocks are formed by subjecting any rock type—sedimentary rock, igneous rock or another older metamorphic rock—to different temperature and pressure conditions than those in which the original rock was formed. This process is called metamorphism; meaning to "change in form". The result is a profound change in physical properties and chemistry of the stone. The original rock, known as the protolith, transforms into other
  8. 8. ECED 7 | Science, Health and Nature Study 8 mineral types or else into other forms of the same minerals, such as by recrystallization. The temperatures and pressures required for this process are always higher than those found at the Earth's surface: temperatures greater than 150 to 200 °C and pressures of 1500 bars. Metamorphic rocks compose 27.4% of the crust by volume. The three major classes of metamorphic rock are based upon the formation mechanism. An intrusion of magma that heats the surrounding rock causes contact metamorphism—a temperature-dominated transformation. Pressure metamorphism occurs when sediments are buried deep under the ground; pressure is dominant and temperature plays a smaller role. This is termed burial metamorphism, and it can result in rocks such as jade. Where both heat and pressure play a role, the mechanism is termed regional metamorphism. This is typically found in mountain-building regions. Depending on the structure, metamorphic rocks are divided into two general categories. Those that possess a texture are referred to as foliated; the remainder are termed non-foliated. The name of the rock is then determined based on the types of minerals present. Schist are foliated rocks that are primarily composed of lamellar minerals such as micas. A gneiss has visible bands of differing lightness, with a common example being the granite gneiss. Other varieties of foliated rock include slates, phyllites, and mylonite. Familiar examples of non- foliated metamorphic rocks include marble, soapstone, and serpentine. This branch contains quartzite—a metamorphosed form of sandstone—and hornfels. The use of rocks has had a huge impact on the cultural and technological development of the human race. Rocks have been used by humans and other hominids for more than 2 million years. Lithic technology marks some of the oldest and continuously used technologies. The mining of rocks for their metal ore content has been one of the most important factors of human advancement, which has progressed at different rates in different places in part because of the kind of metals available from the rocks of a region. Mining Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or (coal) seam. This term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock salt and potash. Mining is required to obtain any material that cannot be grown through agricultural processes, or created artificially in a laboratory or factory. Mining in a wider sense comprises extraction of any non-renewable resource (e.g.,petroleum, natural gas, or even water).
  9. 9. ECED 7 | Science, Health and Nature Study 9 Mining of stone and metal has been done since pre-historic times. Modern mining processes involve prospecting for ore bodies, analysis of the profit potential of a proposed mine, extraction of the desired materials and finally reclamation of the land to prepare it for other uses once the mine is closed. The nature of mining processes creates a potential negative impact on the environment both during the mining operations and for years after the mine is closed. This impact has led to most of the world's nations adopting regulations to moderate the negative effects of mining operations. Safety has long been a concern as well, though modern practices have improved safety in mines significantly. 3. Mirrors A mirror is an object that reflects light in a way that preserves much of its original quality subsequent to its contact with the mirror. Some mirrors also filter out some wavelengths, while preserving other wavelengths in the reflection. This is different from other light-reflecting objects that do not preserve much of the original wave signal other than color and diffuse reflected light. The most familiar type of mirror is the plane mirror, which has a flat surface. Curved mirrors are also used, to produce magnified or diminished images or focus light or simply distort the reflected image. Mirrors are commonly used for personal grooming or admiring oneself (in which case the archaic term looking-glass is sometimes still used), decoration, and architecture. Mirrors are also used in scientific apparatus such as telescopes and lasers, cameras, and industrial machinery. Most mirrors are designed for visible light; however, mirrors designed for other types of waves or other wavelengths of electromagnetic radiation are also used, especially in non- optical instruments. History The first mirrors used by people were most likely pools of dark, still water, or water collected in a primitive vessel of some sort. The earliest manufactured mirrors were pieces of polished stone such as obsidian, a naturally occurring volcanic glass. Examples of obsidian mirrors found in Anatolia (modern-day Turkey) have been dated to around 6000 BC. Polished stone mirrors from Central and South America date from around 2000 BC onwards. Mirrors of polished copper were crafted in Mesopotamia from 4000 BC, and in ancient Egypt from around 3000 BC. In China, bronze mirrors were manufactured from around 2000 BC, some of the earliest bronze and copper examples being produced by the Qijia culture. Mirrors made of other metal mixtures (alloys) such as copper and tin speculum metal may have also been produced in China and
  10. 10. ECED 7 | Science, Health and Nature Study 10 India. Mirrors of speculum metal or any precious metal were hard to produce and were only owned by the wealthy. Metal-coated glass mirrors are said to have been invented in Sidon (modern-day Lebanon) in the first century AD, and glass mirrors backed with gold leaf are mentioned by the Roman author Pliny in his Natural History, written in about 77 AD. The Romans also developed a technique for creating crude mirrors by coating blown glass with molten lead. Parabolic mirrors were described and studied in classical antiquity by the mathematician Diocles in his work On Burning Mirrors. Ptolemy conducted a number of experiments with curved polished iron mirrors, and discussed plane, convex spherical and concave spherical mirrors in his Optics. Parabolic mirrors were also described by the physicist Ibn Sahl in the 10th century, and Ibn al-Haytham discussed concave and convex mirrors in both cylindrical and spherical geometries, carried out a number of experiments with mirrors, and solved the problem of finding the point on a convex mirror at which a ray coming from one point is reflected to another point. By the 11th century, clear glass mirrors were being produced in Moorish Spain. In China, people began making mirrors with the use of silver-mercury amalgams as early as 500 AD.[16] Some time during the earlyRenaissance, European manufacturers perfected a superior method of coating glass with a tin-mercury amalgam. The exact date and location of the discovery is unknown, but in the 16th century, Venice, a city famed for its glass-making expertise, became a centre of mirror production using this new technique. Glass mirrors from this period were extremely expensive luxuries. The Saint-Gobain factory, founded by royal initiative in France, was an important manufacturer, and Bohemian and German glass, often rather cheaper, was also important. The invention of the silvered-glass mirror is credited to German chemist Justus von Liebig in 1835.[18] His process involved the deposition of a thin layer of metallic silver onto glass through the chemical reduction of silver nitrate. This silvering process was adapted for mass manufacturing and led to the greater availability of affordable mirrors. Nowadays, mirrors are often produced by the wet deposition of silver (or sometimes aluminum via vacuum deposition) directly onto the glass substrate. Types of glass mirrors There are many types of glass mirrors, each representing a different manufacturing process and reflection type. An aluminium glass mirror is made of a float glass manufactured using vacuum coating, i.e. aluminium powder is evaporated (or "sputtered") onto the exposed surface of the glass in a vacuum chamber and then coated with two or more layers of waterproof protective paint.
  11. 11. ECED 7 | Science, Health and Nature Study 11 A low aluminium glass mirror is manufactured by coating silver and two layers of protective paint on the back surface of glass. A low aluminium glass mirror is very clear, light transmissive, smooth, and reflects accurate natural colors. This type of glass is widely used for framing presentations and exhibitions in which a precise color representation of the artwork is truly essential or when the background color of the frame is predominantly white. A safety glass mirror is made by adhering a special protective film to the back surface of a silver glass mirror, which prevents injuries in case the mirror is broken. This kind of mirror is used for furniture, doors, glass walls, commercial shelves, or public areas. A silkscreen printed glass mirror is produced using inorganic color ink that prints patterns through a special screen onto glass. Various colors, patterns, and glass shapes are available. Such a glass mirror is durable and more moisture resistant than ordinary printed glass and can serve for over 20 years. This type of glass is widely used for decorative purposes (e.g., on mirrors, table tops, doors, windows, kitchen chop boards, etc.). A silver glass mirror is an ordinary mirror, coated on its back surface with silver, which produces images by reflection. This kind of glass mirror is produced by coating a silver, copper film and two or more layers of waterproof paint on the back surface of float glass, which perfectly resists acid and moisture. A silver glass mirror provides clear and actual images, is quite durable, and is widely used for furniture, bathroom and other decorative purposes. Decorative glass mirrors are usually handcrafted. A variety of shades, shapes and glass thickness are often available. Effects Shape of a mirror's surface A beam of light reflects off a mirror at an angle of reflection equal to its angle of incidence (if the size of a mirror is much larger than the wavelength of light). That is, if the beam of light is shining on a mirror's surface at a ° angle vertically, then it reflects from the point of incidence at a ° angle from vertically in the opposite direction. This law mathematically follows from the interference of a plane wave on a flat boundary (of much larger size than the wavelength). In a plane mirror, a parallel beam of light changes its direction as a whole, while still remaining parallel; the images formed by a plane mirror are virtual images, of the same size as the original object (see mirror image). In a concave mirror, parallel beams of light become a convergent beam, whose rays intersect in the focus of the mirror. Also known as converging mirror
  12. 12. ECED 7 | Science, Health and Nature Study 12 In a convex mirror, parallel beams become divergent, with the rays appearing to diverge from a common point of intersection "behind" the mirror. Spherical concave and convex mirrors do not focus parallel rays to a single point due to spherical aberration. However, the ideal of focusing to a point is a commonly-used approximation. Parabolic reflectors resolve this, allowing incoming parallel rays (for example, light from a distant star) to be focused to a small spot; almost an ideal point. Parabolic reflectors are not suitable for imaging nearby objects because the light rays are not parallel. Mirror image If one looks in a mirror, one's image reverses (e.g., if one raises one's right hand, one's left hand will appear to go up in the mirror). However, a mirror does not "swap" left and right, any more than it swaps top and bottom. A mirror reverses the forward/backward axis, and we define left and right relative to front and back. Flipping front/back and left/right is equivalent to a rotation of 180 degrees about the vertical axis (in the same way that text which is back-to- front and upside-down simply looks like it has been rotated 180 degrees on the page). Therefore, looking at an image of oneself with the front/back axis flipped is the same as looking at an image with the left/right axis flipped and the whole figure rotated 180 degrees about the vertical axis, which is exactly what one sees when standing in front of a mirror. Safety and easier viewing Convex mirrors Convex mirrors provide a wider field of view than flat mirrors, and are often used on vehicles, especially large trucks, to minimize blind spots. They are sometimes placed at road junctions, and corners of sites such as parking lots to allow people to see around corners to avoid crashing into other vehicles or shopping carts. They are also sometimes used as part of security systems, so that a single video camera can show more than one angle at a time. Mouth mirrors or "dental mirrors" Mouth mirrors or "dental mirrors" are used by dentists to allow indirect vision and lighting within the mouth. Their reflective surfaces may be either flat or curved. Mouth mirrors are also commonly used by mechanics to allow vision in tight spaces and around corners in equipment. Rear-view mirrors Rear-view mirrors are widely used in and on vehicles (such as automobiles, or bicycles), to allow drivers to see other vehicles coming up behind them. Some motorcycle helmets have a built-in so-called MROS (Multiple Reflective Optic System): a set of reflective surfaces inside the helmet that together function as a rear-view mirror.[22] On
  13. 13. ECED 7 | Science, Health and Nature Study 13 rear-view sunglasses, the left end of the left glass and the right end of the right glass work as mirrors. One-way mirrors and windows One-way mirrors One-way mirrors (also called two-way mirrors) work by overwhelming dim transmitted light with bright reflected light. A true one-way mirror that actually allows light to be transmitted in one direction only without requiring external energy is not possible as it violates thesecond law of thermodynamics: if one placed a cold object on the transmitting side and a hot one on the blocked side, radiant energy would be transferred from the cold to the hot object. Thus, though a one-way mirror can be made to appear to work in only one direction at a time, it's actually reflective from either side. One-way windows One-way windows can be made to work with polarized light in the laboratory without violating the second law. This is an apparent paradox that stumped some great physicists, although it does not allow a practical one-way mirror for use in the real world. Optical isolators are one-way devices that are commonly used with lasers. Face-to-face mirrors Two or more mirrors placed exactly face to face can give an infinite regress of reflections. Some devices use this to generate multiple reflections: Fabry–Pérot interferometer Laser (which contains an optical cavity) 3D Kaleidoscope to concentrate light[27] momentum-enhanced solar sail Unusual Kinds of Mirrors Other types of reflecting device are also called "mirrors". Acoustic mirrors are passive devices used to reflect and perhaps to focus sound waves. Acoustic mirrors were used for selective detection of sound waves, especially during World War II. They were used for detection of enemy aircraft prior to the development of radar. Acoustic mirrors are used for remote probing of the atmosphere; they can be used to form a narrow diffraction-limited beam.[ They can also be used for underwater imaging. Active mirrors are mirrors that amplify the light they reflect. They are used to make disk lasers.[46] The amplification is typically over a narrow range of wavelengths, and requires an external source of power.
  14. 14. ECED 7 | Science, Health and Nature Study 14 Atomic mirrors are devices which reflect matter waves. Usually, atomic mirrors work at grazing incidence. Such mirrors can be used for atomic interferometry and atomic holography. It has been proposed that they can be used for non-destructive imaging systems withnanometer resolution.[47] Cold mirrors are dielectric mirrors that reflect the entire visible light spectrum, while efficiently transmitting infrared wavelengths. These are the converse of hot mirrors. Corner reflectors use three flat mirrors to reflect light back towards its source. They are used for emergency location, and even laser ranging to the Moon. Hot mirrors reflect infrared light while allowing visible light to pass. These can be used to separate useful light from unneeded infrared to reduce heating of components in an optical device. They can also be used as dichroic beamsplitters. (Hot mirrors are the converse of cold mirrors.) Metallic reflectors are used to reflect infrared light (such as in space heaters or microwaves). Non-reversing mirrors are mirrors that provide a non-reversed image of their subjects. X-ray mirrors produce specular reflection of X-rays. All known types work only at angles near grazing incidence, and only a small fraction of the rays are reflected.[48] See also X-ray optics.