Mirrors and its types
A mirror is an object that reflects light or sound in a way that preserves much of its original quality prior 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.
Manufacturing
Mirrors are manufactured by applying a reflective coating to a suitable substrate. The most common such substrate is glass, due to its transparency, ease of fabrication, rigidity, hardness, and ability to take a smooth finish. The reflective coating is typically applied to the back surface of the glass, so that the reflecting side of the coating is protected from corrosion and accidental damage by the glass on one side and the coating itself and optional paint for further protection on the other.
The Essay on Polarized light lab report
ABSTRACT Ordinary light such as that from a light bulb is a form of wave motion that consists of electrical and magnetic fields that vibrate at right angles to the direction of travel of a light beam. Light waves that vibrate in a single plane are called polarized light waves. Such waves can be produced by passing light through polarizing filters. The experiment conducted was composed of crossed ...
In classical antiquity, mirrors were made of solid metal (bronze, later silver) and were too expensive for widespread use; they were also prone to corrosion. Due to the low reflectivity of polished metal, these mirrors also gave a darker image than modern ones, making them unsuitable for indoor use with the artificial lighting of the time (candles or lanterns).[citation needed]
The method of making mirrors out of plate glass was invented by 16th-century Venetian glassmakers on the island of Murano, who covered the back of the glass with mercury, obtaining near-perfect and undistorted reflection. For over one hundred years, Venetian mirrors installed in richly decorated frames served as luxury decorations for palaces throughout Europe, but the secret of the mercury process eventually arrived in London and Paris during the 17th century, due to industrial espionage. French workshops succeeded in large scale industrialization of the process, eventually making mirrors affordable to the masses, although mercury’s toxicity remained a problem[citation needed].
In modern times, the mirror substrate is shaped, polished and cleaned, and is then coated. Glass mirrors are most often coated with non-toxic silver or aluminium, implemented by a series of coatings:[citation needed]
Tin (II) chloride
Silver
Chemical activator [disambiguation needed]
Copper
Paint
The tin(II) chloride is applied because silver will not bond with the glass. The activator causes the tin/silver to harden. Copper is added for long-term durability.[20] The paint protects the coating on the back of the mirror from scratches and other accidental damage.[citation needed]
In some applications, generally those that are cost-sensitive or that require great durability, mirrors are made from a single, bulk material such as polished metal.[citation needed] For technical applications such as laser mirrors, the reflective coating is typically applied by vacuum deposition on the front surface of the substrate. This eliminates double reflections (a weak reflection from the surface of the glass, and a stronger one from the reflecting metal) and reduces absorption of light by the mirror. Technical mirrors may use a silver, aluminium, or gold coating (the latter typically for infrared mirrors), and achieve reflectivities of 90–95% when new. A protective transparent overcoat may be applied to prevent oxidation of the reflective layer. Applications requiring higher reflectivity or greater durability, where wide bandwidth is not essential, use dielectric coatings, which can achieve reflectivities as high as 99.999% over a narrow range of wavelengths.[citation needed.
The Essay on Glass Industry
Glass is best packaging material in preserving taste, aroma, and nutritional values of the food. Glass is environment friendly and has tremendous growth opportunities in India, as India is one of the fastest growing economies in the world. The size of the glass industry in India is around $2. 5 billion, out of which the container glass industry is around $0. 87 billion. The major consumer ...
Types of glass mirror
18th century vermeil mirror in the Musée des Arts décoratifs, Strasbourg
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 is spread over the glass in the vacuum chamber and then coated with two or more layers of waterproof protective paint. An aluminium glass mirror provides an actual and accurate reflection.[citation needed]
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.[citation needed]
A safety glass mirror is made by sticking a special protective film on 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.[citation needed]
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.).[citation needed]
The Essay on Prism Reflecting Light
Light Effects Refraction, reflection and dispersion are all processes which happen when a ray of light is shone at either a glass block, a mirror or a prism. The ray box is the light source. Mirror When the ray box is shone at a mirror the angle of incidence is always a few degrees different to the angle of reflection. For example, if you shine a light ray into a mirror at 60* then it will reflect ...
A silver glass mirror is an ordinary mirror, coated on its back surface with silver, that 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.[citation needed]
Decorative glass mirrors are usually handcrafted. A variety of shades, shapes and glass thickness are often available. [Citation needed]
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 θ° angle vertically, then it reflects from the point of incidence at a θ° 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 becomes a convergent beam, whose rays intersect in the focus of the mirror.
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.
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.[citation needed]
The Term Paper on Light Quality On The Rate Of Photosynthesis Measure
Abstract This study was undertaken to determine the relationship of different wavelengths of light and the rate of photosynthesis in spinach leafs. The rate of photosynthesis was measured every five min under light colors of white, green, red, blue and yellow under a light intensity of 2000 lux. The rate of photosynthesis was measured by the spinach disk method in which we replaced the air from ...
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 engineers to allow vision in tight spaces and around corners in equipment.
Rear-view mirrors
A mirror on a racing car.
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.[1] On rear-view sunglasses, the left end of the left glass and the right end of the right glass work as mirrors.
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Two-way versus one-way mirrors and windows
Main article: Two-way mirror
Two-way mirrors
A two-way mirror is a sheet of glass coated with a layer of metal only a few dozen atoms thick, which reflects some percentage of the light incident on it and transmits the remainder to the other side.
One-way mirrors
One-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 the second 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.
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.[21][22] Optical isolators are one-way devices that are commonly used with lasers.
The Essay on On the Soul:Plato, Aristotle, Augustine
Psyche’ or the soul, is a intricate part of our being which many great thinkers such as Plato, Aristotle and Augustine aim to define and unravel. One should remain attentive to the fact that these great minds come to similar yet altered conclusions of the soul; for it is an intrinsic part of our being, aiding in our discovery and understanding of the world. Plato addresses in his novel, The ...
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Signalling
Main article: Heliograph
With the sun as light source, a mirror can be used to signal by variations in the orientation of the mirror. The signal can be used over long distances, possibly up to 60 kilometres on a clear day. This technique was used by Native American tribes and numerous militaries to transmit information between distant outposts.
Mirrors can also be used for rescue to attract the attention of search and rescue helicopters. Specialized signalling mirrors are available and are often included in military survival kits.
Technology
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Televisions and projectors
Microscopic mirrors are a core element of many of the largest high-definition televisions and video projectors. A common technology of this type is Texas Instruments’ DLP. A DLP chip is a postage stamp-sized microchip whose surface is an array of millions of microscopic mirrors. The picture is created as the individual mirrors move to either reflect light toward the projection surface (pixel on), or toward a light absorbing surface (pixel off).
Other projection technologies involving mirrors include LCoS. Like a DLP chip, LCoS is a microchip of similar size, but rather than millions of individual mirrors, there is a single mirror that is actively shielded by a liquid crystal matrix with up to millions of pixels. The picture is formed as light is either reflected toward the projection surface (pixel on), or absorbed by the activated LCD pixels (pixel off).
LCoS-based televisions and projectors often use 3 chips, one for each primary color.
Large mirrors are used in rear projection televisions. Light (for example from a DLP as mentioned above) is “folded” by one or more mirrors so that the television set is compact.
Instruments
Telescopes and other precision instruments use front silvered or first surface mirrors, where the reflecting surface is placed on the front (or first) surface of the glass (this eliminates reflection from glass surface ordinary back mirrors have).
The Essay on All About Light-Physics
LIGHT * Light is part of the electromagnetic spectrum, the spectrum is the collection of all waves, which include visible light, Microwaves, radio waves ( AM, FM, SW ), X-Rays, and Gamma Rays. * In the late 1600s, important questions were raised, asking if light is made up of particles, or is it waves .? * Sir Isaac Newton, held the theory that light was made up of tiny particles. In 1678, Dutch ...
Some of them use silver, but most are aluminium, which is more reflective at short wavelengths than silver. All of these coatings are easily damaged and require special handling. They reflect 90% to 95% of the incident light when new. The coatings are typically applied by vacuum deposition. A protective overcoat is usually applied before the mirror is removed from the vacuum, because the coating otherwise begins to corrode as soon as it is exposed to oxygen and humidity in the air. Front silvered mirrors have to be resurfaced occasionally to keep their quality. There are optical mirrors such as mangin mirrors that are second surface mirrors (reflective coating on the rear surface) as part of their optical designs, usually to correct optical aberrations.[23]
The reflectivity of the mirror coating can be measured using a reflectometer[disambiguation needed] and for a particular metal it will be different for different wavelengths of light. This is exploited in some optical work to make cold mirrors and hot mirrors. A cold mirror is made by using a transparent substrate and choosing a coating material that is more reflective to visible light and more transmissive to infrared light. A hot mirror is the opposite, the coating preferentially reflects infrared. Mirror surfaces are sometimes given thin film overcoatings both to retard degradation of the surface and to increase their reflectivity in parts of the spectrum where they will be used. For instance, aluminum mirrors are commonly coated with silicon dioxide or magnesium fluoride. The reflectivity as a function of wavelength depends on both the thickness of the coating and on how it is applied.
A dielectric coated mirror used in a dye laser. The mirror is over 99% reflective at 550 nanometers, (yellow), but will allow most other colors to pass through.
A dielectric mirror used in lasers
For scientific optical work, dielectric mirrors are often used. These are glass (or sometimes other material) substrates on which one or more layers of dielectric material are deposited, to form an optical coating. By careful choice of the type and thickness of the dielectric layers, the range of wavelengths and amount of light reflected from the mirror can be specified. The best mirrors of this type can reflect >99.999% of the light (in a narrow range of wavelengths) which is incident on the mirror. Such mirrors are often used in lasers.
In astronomy, adaptive optics is a technique to measure variable image distortions and adapt a deformable mirror accordingly on a timescale of milliseconds, to compensate for the distortions.
Although most mirrors are designed to reflect visible light, surfaces reflecting other forms of electromagnetic radiation are also called “mirrors”. The mirrors for other ranges of electromagnetic waves are used in optics and astronomy. Mirrors for radio waves are important elements of radio telescopes.
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Face-to-face mirrors
Two or more mirrors placed exactly face to face give the appearance of an infinite regress. Some devices use this to generate multiple reflections:
Fabry–Pérot interferometer
Laser (which contains an optical cavity)
some types of catoptric cistula
momentum-enhanced solar sail
Mirrors and superstition
There are many legends and superstitions surrounding mirrors. Mirrors are said to be a reflection of the soul, and they were often used in traditional witchcraft as tools for scrying or performing other spells. It is also said that mirrors cannot lie. They can show only the truth, so it is a bad omen to see something in a mirror which should not be there. Also there is a legend that a newborn child should not see a mirror until its first birthday as its soul is still developing. If the child sees its reflection it is said that it will die.
It is a common superstition that someone who breaks a mirror will receive seven years of bad luck.[28] The reason for this belief is that the mirror is believed to reflect part of the soul. Therefore, breaking a mirror will break part of the soul. However, the soul is said to regenerate every seven years, thus coming back unbroken.[citation needed] To prevent a broken mirror from reflecting a broken soul during the seven-year interim, one of many rituals must be performed. Two alternatives include grinding the broken mirror to dust (perhaps the easiest approach)[29] or burying the mirror.[citation needed] It is also said that tapping the broken mirror on a gravestone seven times will allow the soul to heal. However, if the mirror is both touched to the gravestone and buried, the bad luck will remain. The only course of action for one in this position is to dig up the mirror and grind it to dust. This dust must be sprinkled around the same gravestone on which the mirror was initially tapped.[citation needed]
There is a Buddhist belief that negative spirits will enter houses through the door if they have triangular-shaped roofs. Hanging a small circular mirror in front of the door will prevent the bad spirits from entering.[citation needed]
In days past, it was customary in the southern United States to cover the mirrors in a house where the wake of a deceased person was being held. It was believed that the person’s soul would become trapped in a mirror if it was left uncovered. This practice is still followed in other countries (e.g., Romania), extending to everything that could reflect the deceased person’s face (such as TVs and appliances).
Another explanation given is that the devil will appear in the reflection of the dead. Mirrors falling from walls or otherwise breaking or cracking mysteriously were said to be haunted. A similar custom existed in Greece, in the belief that use of mirrors is a sign of vanity that does not become mourning. (Other Greek mourning customs include not playing music, not entertaining guests, and using no festive decorations, e.g. on Christmas, during the customary year-long mourning period).[citation needed]
According to legend, a vampire has no reflection in mirrors because it is an undead creature and has already lost its soul.[citation needed]
Another superstition claims it is bad luck to have two mirrors facing each other.[citation needed]
A staple of childhood slumber parties is the game Bloody Mary, which involves chanting “Bloody Mary” three times in a darkened room while staring into a mirror. There are many versions of the game, but the general idea is that “Mary” will appear in the mirror and attempt to harm or kill the person who has summoned her. Thanks to a series of popular horror movies based on a supernatural killer who haunted mirrors, the phrase “Candyman” may be substituted for Mary.[citation needed]
