pHysiCs bLog

Saturday, August 11, 2007

im here again!
hehehe
anu keah yung periodic test sa physics?!?
hai naku!
siguradong mahirap yun at kelangan mag-aral ng mabuti!
tulad nga ng sabi ni sir....
"mendel mag-aral ha!"
hehehe
peace poh tayo!
kung sa long test mababa ang score kelangan bumawi para lang family day!
buti nah nga lng wala ng kelangan ipasa tapos nah din ang life of a mirror project at sana talaga matuwa si sir mendoza sa gawa namen!
hehehe...XD

she told the story ... 1:03 AM

Friday, August 10, 2007

hai naku!
ulitin daw bah ang pagpopost ng vectors?!?
kasi naman eh!
sa libro q lng kihuha toh!
next time i will do my best to make my blog beautiful...
hehehe
and HOPE na maapreciate ni sir toh!...
hehehe
anhirap umulit ng blog eh!

she told the story ... 6:16 AM

Vectors

>solving the resultant of the vectors using Graphical Method
1. With itstail at the origin, draw the 1st vector and properly label it.

2. Then, draw the tail of the 2nd vector at the head of the 1st vector.

3. The resultant vector is an arrow drawn from the tail of the 1st vector to the head of the 2nd vector.

4. Using a ruler, measure the length of the resultant vector. Then convert this length back to the original using the scale. This is the magnitude. Using a protractor, measure angle theta. This is the direction.>

>solving the resultant of the vectors using Component method

1. First, break down each vector into its x- and y- components.

2. Add all the x-components together. Add all the y-components together. The total x-component will be the x-component of the resultant Rx and the total y-component will be the y-component of the resultant Ry

she told the story ... 6:12 AM

An optical fiber (or fibre) is a glass or plastic fiber designed to guide light along its length by confining as much light as possible in a propagating form. In fibers with large core diameter, the confinement is based on total internal reflection. In smaller diameter core fibers, (widely used for most communication links longer than 200 meters) the confinement relies on establishing a waveguide. Fiber optics is the overlap of applied science and engineering concerned with such optical fibers. Optical fibers are widely used in fiber-optic communication, which permits transmission over longer distances and at higher data rates than other forms of wired and wireless communications. They are also used to form sensors, and in a variety of other applications.
The term optical fiber covers a range of different designs including graded-index optical fibers, step-index optical fibers, birefringent polarization-maintaining fibers and more recently photonic crystal fibers, with the design and the wavelength of the light propagating in the fiber dictating whether or not it will be multi-mode optical fiber or single-mode optical fiber. Because of the mechanical properties of the more common glass optical fibers, special methods of splicing fibers and of connecting them to other equipment are needed. Manufacture of optical fibers is based on partially melting a chemically doped preform and pulling the flowing material on a draw tower. Fibers are built into different kinds of cables depending on how they will be used.

History
The light-guiding principle behind optical fibers was first demonstrated in by Daniel Colladon and Jaques Babinet in the 1840s, with Irish inventor John Tyndall offering public displays using water-fountains ten years later.[1] Practical applications, such as close internal illumination during dentistry, appeared early in the twentieth century. Image transmission through tubes was demonstrated independently by the radio experimenter Clarence Hansell and the television pioneer John Logie Baird in the 1920s. The principle was first used for internal medical examinations by Heinrich Lamm in the following decade. In 1952 physicist Narinder Singh Kapany conducted experiments that led to the invention of optical fiber, based on Tyndall's earlier studies; modern optical fibers, where the glass fiber is coated with a transparent cladding to offer a more suitable refractive index, appeared later in the decade.[1] Development then focused on the development of fiber bundles for image transmission. The first fiber optic semi-flexible gastroscope was patented by Basil Hirschowitz, C. Wilbur Peters, and Lawrence E. Curtiss, researchers at the University of Michigan, in 1956. In the process of developing the gastroscope, Curtiss produced the first glass-clad fibers; previous optical fibers had relied on air or impractical oils and waxes as the low-index cladding material. A variety of other image transmission applications soon followed. Optical fibers became practical for use in communications in the late 1970s, once the attenuation was reduced sufficiently; since then, several technical advances have been made to improve the attenuation and dispersion properties of optical fibers (i.e., allowing signals to travel farther and carry more information), and lower the cost of fiber communications systems.
In 1965, Charles K. Kao and George A. Hockham of the British company Standard Telephones and Cables were the first to suggest that attenuation of contemporary fibers was caused by impurities, which could be removed, rather than fundamental physical effects such as scattering. They speculated that optical fiber could be a practical medium for communication, if the attenuation could be reduced below 20 dB per kilometer (Hecht, 1999, p. 114).This attenuation level was first achieved in 1970, by researchers Robert D. Maurer, Donald Keck, Peter C. Schultz, and Frank Zimar working for American glass maker Corning Glass Works, now Corning Inc. They demonstrated a fiber with 17 dB optic attenuation per kilometer by doping silica glass with titanium. A few years later they produced a fiber with only 4 db/km using germanium oxide as the core dopant. Such low attenuations ushered in optical fiber telecommunications and enabled the Internet.
The erbium-doped fiber amplifier, which reduced the cost of long-distance fiber systems by reducing or even in many cases eliminating the need for optical-electrical-optical repeaters, was invented by David Payne of the University of Southampton, and Emmanuel Desurvire at Bell Laboratories in 1986. The two pioneers were awarded the Benjamin Franklin Medal in Engineering in 1998.
In 1991, the emerging field of photonic crystals led to the development of photonic crystal fiber (Science (2003), vol 299, page 358), which guides light by means of diffraction from a periodic structure, rather than total internal reflection. The first photonic crystal fibers became commercially available in 1996 [1]. Photonic crystal fibers can be designed to carry higher power than conventional fiber, and their wavelength dependent properties can be manipulated to improve their performance in certain application

Applications

Optical fiber communication
Main article: Fiber-optic communication
Optical fiber can be used as a medium for telecommunication and networking because it is flexible and can be bundled as cables. It is especially advantageous for long-distance communications, because light propagates through the fiber with little attenuation compared to electrical cables. This allows long distances to be spanned with few repeaters. Additionally, the light signals propagating in the fiber can be modulated at rates as high as 40 Gb/s[citation needed], and each fiber can carry many independent channels, each by a different wavelength of light. In total, a single fiber-optic cable can carry data at rates as high as 14.4 Pb/s (circa 14 million Gb/s).[citation needed] Over short distances, such as networking within a building, fiber saves space in cable ducts because a single fiber can carry much more data than a single electrical cable. Fiber is also immune to electrical interference, which prevents cross-talk between signals in different cables and pickup of environmental noise. Because they are non-electrical, fiber cables can be used in environments where explosive fumes are present, without danger of ignition.
Although fibers can be made out of transparent plastic, glass, or a combination of the two, the fibers used in long-distance telecommunications applications are always glass, because of the lower optical attenuation. Both multi-mode and single-mode fibers are used in communications, with multi-mode fiber used mostly for short distances (up to 500 m), and single-mode fiber used for longer distance links. Because of the tighter tolerances required to couple light into and between single-mode fibers; single-mode transmitters, receivers, amplifiers and other components are generally more expensive than multi-mode components.

Fiber optic sensors
Optical fibers can be used as sensors to measure strain, temperature, pressure and other parameters. The small size and the fact that no electrical power is needed at the remote location gives the fiber optic sensor advantages to conventional electrical sensor in certain applications.
Optical fibers are used as hydrophones for seismic or SONAR applications. Hydrophone systems with more than 100 sensors per fiber cable have been developed. Hydrophone sensor systems are used by the oil industry as well as a few countries' navies. Both bottom mounted hydrophone arrays and towed streamer systems are in use. The German company Sennheiser developed a microphone working with a laser and optical fibers[2].
Optical fiber sensors for temperature and pressure have been developed for downhole measurement in oil wells. The fiber optic sensor is well suited for this environment as it is functioning at temperatures too high for semiconductor sensors (Distributed Temperature Sensing).
Another use of the optical fiber as a sensor is the optical gyroscope which is in use in the Boeing 767 and in some car models (for navigation purposes) and the use in Hydrogen microsensors.
Fiber-optic sensors have been developed to measure co-located temperature and strain simultaneously with very high accuracy[3]. This is particularly useful to acquire information from small complex structures.

Other uses of optical fibers

A frisbee illuminated by fiber optics
Fibers are widely used in illumination applications. They are used as light guides in medical and other applications where bright light needs to be shone on a target without a clear line-of-sight path. In some buildings, optical fibers are used to route sunlight from the roof to other parts of the building (see non-imaging optics). Optical fiber illumination is also used for decorative applications, including signs, art, and artificial Christmas trees. Swarovski boutiques use optical fibers to illuminate their crystal showcases from many different angles while only employing one light source. Optical fiber is an intrinsic part of the light-transmitting concrete building product, LiTraCon.

A fiber-optic Christmas Tree
Optical fiber is also used in imaging optics. A coherent bundle of fibers is used, sometimes along with lenses, for a long, thin imaging device called an endoscope, which is used to view objects through a small hole. Medical endoscopes are used for minimally invasive exploratory or surgical procedures (endoscopy). Industrial endoscopes (see fiberscope or borescope) are used for inspecting anything hard to reach, such as jet engine interiors.
An optical fiber doped with certain rare-earth elements such as erbium can be used as the gain medium of a laser or optical amplifier. Rare-earth doped optical fibers can be used to provide signal amplification by splicing a short section of doped fiber into a regular (undoped) optical fiber line. The doped fiber is optically pumped with a second laser wavelength that is coupled into the line in addition to the signal wave. Both wavelengths of light are transmitted through the doped fiber, which transfers energy from the second pump wavelength to the signal wave. The process that causes the amplification is stimulated emission.
Optical fibers doped with a wavelength shifter are used to collect scintillation light in physics experiments.
Optical fiber can be used to supply a low level of power (around one watt) to electronics situated in a difficult electrical environment. Examples of this are electronics in high-powered antenna elements and measurement devices used in high voltage transmission equipment.

Principle of operation
An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process of total internal reflection. The fiber consists of a core surrounded by a cladding layer. To confine the optical signal in the core, the refractive index of the core must be greater than that of the cladding. The boundary between the core and cladding may either be abrupt, in step-index fiber, or gradual, in graded-index fiber.

Multimode fiber

The propagation of light through a multi-mode optical fiber.
Fiber with large (greater than 10 μm) core diameter may be analyzed by geometric optics. Such fiber is called multimode fiber, from the electromagnetic analysis (see below). In a step-index multimode fiber, rays of light are guided along the fiber core by total internal reflection. Rays that meet the core-cladding boundary at a high angle (measured relative to a line normal to the boundary), greater than the critical angle for this boundary, are completely reflected. The critical angle (minimum angle for total internal reflection) is determined by the difference in index of refraction between the core and cladding materials. Rays that meet the boundary at a low angle are refracted from the core into the cladding, and do not convey light and hence information along the fiber. The critical angle determines the acceptance angle of the fiber, often reported as a numerical aperture. A high numerical aperture allows light to propagate down the fiber in rays both close to the axis and at various angles, allowing efficient coupling of light into the fiber. However, this high numerical aperture increases the amount of dispersion as rays at different angles have different path lengths and therefore take different times to traverse the fiber. A low numerical aperture may therefore be desirable.
In graded-index fiber, the index of refraction in the core decreases continuously between the axis and the cladding. This causes light rays to bend smoothly as they approach the cladding, rather than reflecting abruptly from the core-cladding boundary. The resulting curved paths reduce multi-path dispersion because high angle rays pass more through the lower-index periphery of the core, rather than the high-index center. The index profile is chosen to minimize the difference in axial propagation speeds of the various rays in the fiber. This ideal index profile is very close to a parabolic relationship between the index and the distance from the axis.

Singlemode fiber

A typical single-mode optical fiber, showing diameters of the component layers.
Fiber with a core diameter less than about ten times the wavelength of the propagating light cannot be modeled using geometric optics. Instead, it must be analyzed as an electromagnetic structure, by solution of Maxwell's equations as reduced to the electromagnetic wave equation. The electromagnetic analysis may also be required to understand behaviors such as speckle that occur when coherent light propagates in multi-mode fiber. As an optical waveguide, the fiber supports one or more confined transverse modes by which light can propagate along the fiber. Fiber supporting only one mode is called single-mode or mono-mode fiber. The behavior of larger-core multimode fiber can also be modeled using the wave equation, which shows that such fiber supports more than one mode of propagation (hence the name). The results of such modeling of multi-mode fiber approximately agree with the predictions of geometric optics, if the fiber core is large enough to support more than a few modes.
The waveguide analysis shows that the light energy in the fiber is not completely confined in the core. Instead, especially in single-mode fibers, a significant fraction of the energy in the bound mode travels in the cladding as an evanescent wave.
The most common type of single-mode fiber has a core diameter of 8 to 10 μm and is designed for use in the near infrared. The mode structure depends on the wavelength of the light used, so that this fiber actually supports a small number of additional modes at visible wavelengths. Multi-mode fiber, by comparison, is manufactured with core diameters as small as 50 microns and as large as hundreds of microns.

Special-purpose fiber
Some special-purpose optical fiber is constructed with a non-cylindrical core and/or cladding layer, usually with an elliptical or rectangular cross-section. These include polarization-maintaining fiber and fiber designed to suppress whispering gallery mode propagation.

Materials
Glass optical fibers are almost always made from silica, but some other materials, such as fluorozirconate, fluoroaluminate, and chalcogenide glasses, are used for longer-wavelength infrared applications. Like other glasses, these glasses have a refractive index of about 1.5. Typically the difference between core and cladding is less than one percent.
Plastic optical fiber (POF) is commonly step-index multimode fiber, with core diameter of 1 mm or larger. POF typically has much higher attenuation than glass fiber (that is, the amplitude of the signal in it decreases faster), 1 dB/m or higher, and this high attenuation limits the range of POF-based systems.

Fiber fuse
At high optical intensities, above 2 megawatts per square centimetre, when a fiber is subjected to a shock or is otherwise suddenly damaged, a fiber fuse can occur. The reflection from the damage vaporizes the fiber immediately before the break, and this new defect remains reflective so that the damage propagates back toward the transmitter at 1–3 meters per second [4],[5],[6]. The open fiber control system, which ensures laser eye safety in the event of a broken fiber, can also effectively halt propagation of the fiber fuse [7]. In situations, such as undersea cables, where high power levels might be used without the need for open fiber control, a "fiber fuse" protection device at the transmitter can break the circuit to prevent any damage.

she told the story ... 5:49 AM

Tuesday, August 7, 2007

(Concave)

Ray diagrams can be used to determine the image location, size, orientation and type of image formed of objects when placed at a given location in front of a concave mirror. Ray diagrams provide useful information about object-image relationships, yet fail to provide the information in a quantitative form. While a ray diagram may help one determine the approximate location and size of the image, it will not provide numerical information about image distance and object size. To obtain this type of numerical information, it is necessary to use the Mirror equation and the Magnification equation. The mirror equation expresses the quantitative relationship between the object distance (do), the image distance (di), and the focal length (f). The equation is stated as follows:

The Magnification equation relates the ratio of the image distance and object distance to the ratio of the image height (hi) and object height (ho). The magnification equation is stated as follows:

These two equations can be combined to yield information about the image distance and image height if the object distance, object height, and focal length are known.

(Convex)

Ray diagrams can be used to determine the image location, size, orientation and type of image formed of objects when placed at a given location in front of a mirror.Ray diagrams provide useful information about object-image relationships, yet fail to provide the information in a quantitative form. While a ray diagram may help one determine the approximate location and size of the image, it will not provide numerical information about image distance and object size. To obtain this type of numerical information, it is necessary to use the Mirror equation and the Magnification equation. The mirror equation expresses the quantitative relationship between the object distance (do), the image distance (di), and the focal length (f). The equation is stated as follows:

The Magnification equation relates the ratio of the image distance and object distance to the ratio of the image height (hi) and object height (ho). The magnification equation is stated as follows:

These two equations can be combined to yield information about the image distance and image height if the object distance, object height, and focal length are known.

she told the story ... 9:56 PM

SIMILARITIES BETWEEN AN EYE AND A CAMERA

The eye is not a camera but there are some similarities.The focal length of the eye is about 17
mm (2/3"). We see almost 180 degrees wide, 120 degrees high, in a goggle format.PUPIL/ Iris/ diaphragm: restricts light. From f-2.0 to f-10. A ratio of 25 to 1 or 5 f-stops. Open is dilated, closed is constricted.RODS: The more sensitive RECEPTORS of light in the RETINA. There are 120 million rods and they are color blind. The RODS drastically change SENSITIVITY with different light conditions. They need 50 minutes to completely DARK ADAPT and about 30 seconds to LIGHT ADAPT. The eye has a range of SENSITIVITY of 10 million to one. A candle 17 miles away can be seen on a clear night by a dark adapted eye. On the bright side we can VERY CAREFULLY look at the sun partly obscured a cloud. DO NOT LOOK AT A BRIGHT SUN DIRECTLY.CONES: The less sensitive COLOR RECEPTORS in the RETINA. 6 million total. Three kinds of cones, red blue and green, together they can discriminate 200 different hues (colors) of light.FOVEA: A 1/50 inch (mechanical pencil lead size) area of all CONES in the back center of the eye's retina. This is the only area of the retina with high resolution. Most of our "seeing" is dependent upon the fovea "scanning" our environment. Each of the 35,000 CONES in the FOVEA has it's own nerve to the brain and can send whole images to the brain at one time. A camcorder CHIP has about 400,000 receptors (pixels) but sends information in a stream. The FOVEA "sees" an angle of only 1.7 degrees, about the size of a pen held at arms length. Outside of the fovea the eye's resolution is very poor.DEMO: Hold your hand outside your central vision with the fingers extended. Try to count the number of fingers on your hand without shifting concentration to them. You hand is just a blur.RESOLUTION: The eye can see a wire the size of a pencil lead at the end of a football field. That is an angle of .004 degrees. (The fovea "sees" 1.7 degrees). If a TV set is 8 feet away and is 16 inches high your eye should be able to resolve the 400 lines the set is capable of. If the set is further away the TV set's resolution is wasted. The eye has the best resolution in bright light.The eye has no FRAME LINES. Although the eye can make very fine discriminations in color and brightness, it cannot make absolute brightness measurements. It won't do as a light meter unless it has an object of known brightness in the scene to compare with.Our eyes scan the world at an amazing rate. They move as fast as 1/50 of a second to look at some detail then stops for as short as 1/20 of a second, that information is sent to the brain and then the eyes scans again for new details.The eye's scan is controlled by our brain, often with no conscious effort. Scanning is directed by our brain to things that interest us. Scanning is accomplished by the muscles in our eye socket that move the eye so rapidly. Things relevant to our physical survival are scanned first. Next we scan for our species survival. (The opposite sex.)If we can see 180 degrees wide with the whole retina and only 1.7 degrees in high definition (the fovea telescope - spot light), you might say that the eye has a 1.7 to 180 degree zoom ability. That's equivalent to a 8 mm to 800 mm lens on a still camera or a 100 to 1 zoom ratio. This all happens automatically without our thinking about it. What's missing are the frame lines that cameras, TVs, movie screens and pictures have.What's the point? Our eye does all this automatically and we aren't even aware of it. So it's easy for our eyes to fool us. The eye is not a camera, cameras only includes what we tell them to include.If the fovea is for high detail seeing, what is the rest of the eye for? The rest of the eye helps us not trip into things, helps us drive down narrow alleys without hitting the walls or trash cans, or duck a fast ball. It helps us orient our bodies in space.If the eye gave us only a foveal vision, like a telescope, life would be tough. Cup your hands to see a small opening and imagine walking around the world. We would trip, get hit and generally have a tough time. Having the fovea scan different images (accomplished by moving the eyeball in its socket) is a lot easier than moving our head around to see different things as most birds have to do.Outside the fovea the rest of the retina has 120 million rods that only see in black and white. They help tell our brain how light or dark an area is relative to the rest of the image, remember, only the cones see colors. The rods are the sensors of the retina that control the pupil / iris so that the right amount of light enters the eye and doesn't over saturate the cones. Just like auto exposure on a many cameras the rods tell the brain to tell the iris to open or close the pupil. Along with the rods in the rest of the retina there are about 6 million more cones. These rods and cones combine to send a much less detailed images to the brain, but from a very wide angle of view. The information sent by the non-fovea area is shape, pattern and recognition information, but not fine detail. Much of this information is used unconsciously and is dependent upon previous learning to make sense of the images we have seen.It is probably to our advantage that the rest of the eye sends only vague information, because an avalanche of information would be produced if the whole eye sent high quality information. Our brain would be overloaded.

she told the story ... 9:42 PM

LENS

The Anatomy of a Lens

If a piece of glass or other transparent material takes on the appropriate shape, it will be capable of taking parallel rays of incident light and either converging them to a point or appear to diverge them from a point. Such a piece of glass is referred to as a lens.

A lens is merely a carefully ground or molded piece of transparent material which refracts light rays in such as way as to form an image. Lenses can be thought of as a series of tiny refracting lenses, each of which refracts light to produce their own image. When these prisms act together, they produce a bright enough image focused at a point.
There are a variety of types of lenses. Lenses differ from one another in terms of their shape and the materials from which they are made. Our focus will be upon lenses which are symmetrical across their horizontal axis - known as the principal axis. In this unit, we will categorize lenses as converging lenses and diverging lenses. A converging lens is a lens which converges rays of light which are traveling parallel to its principal axis. Converging lenses can be identified by their shape; they are thicker across their middle and thinner at their upper and lower edges. A diverging lens is a lens which diverges rays of light which are traveling parallel to its principal axis. Diverging lenses can also be identified by their shape; they are thinner across their middle and thicker at their upper and lower edges.

If a symmetrical lens is thought of as being a slice of a sphere, then there would be a line passing through the center of the sphere and attaching to the mirror in the exact center of the lens. This imaginary line is known as the principal axis. A lens also has an imaginary vertical axis which bisects the symmetrical lens in two. As mentioned above, light rays incident towards either face of the lens and traveling parallel to the principal axis will either converge or diverge. If the light rays converge (as in a converging lens), then they will converge to a point. This point is known as the focal point of the converging lens. If the light rays diverge(as in a diverging lens), then the diverging rays can be traced backwards until they intersect at a point. This point is known as the focal point of a diverging lens. The focal point is denoted by the letter F on the diagrams below. Note that each lens has two focal points - one on each side of the lens. Unlike mirrors, lenses can allow light to pass through either face, depending on where the incident rays are coming from. Subsequently, every lens has two possible focal points. The distance from the mirror to the focal point is known as the focal length (abbreviated by "f"). Technically, a lens does not have a center of curvature (at least not one which has any importance to our discussion). However a lens does have an imaginary point which we refer to as the 2F point. This is the point on the principal axis which is twice as far from the vertical axis as the focal point is.

she told the story ... 8:54 PM