Monday, September 26, 2011
If you are interested to join the Singpaore Amazing Flying Machine Competition 2012,
Please look register at the following URL http://tiny.cc/safmc2012.
If you would like to clarify any doubts do look for Mr Tan HT.
Thursday, August 25, 2011
bi) How are they similar?
They are all closed circuits and the current flows from the positive to the negative points.
bii) The arrangements in the broken circuits are open circuits while the arrangement of the circuits that light up are closed circuits
Done by: Cherin, Jun Wei, Tim
Tuesday, August 23, 2011
Monday, August 22, 2011
Sound (Concepts learn in General Wave Properties is needed.)
MCQ - 10 marks
Short Structure Question - 25 marks
Long Question - 10 marks
Total: 45 marks
Things to bring:
Writing materials including pencil
Wednesday, August 10, 2011
Optical fiber typically consists of a transparent core surrounded by a transparent cladding material with a lower index of refraction. Light is kept in the core by total internal reflection This causes the fiber to act as a waveguide. Fibers that support many propagation paths or transverse modes are called multi-mode fibers.
The following contains information on the placement of fiber optic cables in various indoor and outdoor environments. In general, fiber optic cable can be installed with many of the same techniques used with conventional copper cables. Basic guidelines that can be applied to any type of cable installation are as follows:
- Conduct a thorough site survey prior to cable placement.
- Develop a cable pulling plan.
- Follow proper procedures.
- Do not exceed cable minimum bend radius.
- Do not exceed cable maximum recommended load.
- Document the installation.
Tuesday, August 2, 2011
Make diamonds sparkle
- Optical Fibre (endoscopes, telecommunication)
- “When light traveling in an optical dense medium hits a boundary at a steep angle (larger than the "critical angle" for the boundary), the light will be completely reflected. This is called total internal reflection. This effect is used in optical fibers to confine light in the core. Light travels along the fiber bouncing back and forth off of the boundary. Because the light must strike the boundary with an angle greater than the critical angle, only light that enters the fiber within a certain range of angles can travel down the fiber without leaking out. This range of angles is called the acceptance cone of the fiber. The size of this acceptance cone is a function of the refractive index difference between the fiber's core and cladding.” http://en.wikipedia.org/wiki/Optical_fiber
- Rain Sensors to control automatic windscreen wipers
- “The most common modern rain sensors are based on the principle total internal reflection. An infrared light is beamed at a 45-degree angle into the windshield from the interior — if the glass is wet, less light makes it back to the sensor, and the wipers turn on.” http://en.wikipedia.org/wiki/Rain_sensor#Automotive_sensors
- Fingerprinting Devices
- Uses frustrated Total Internal Reflection in order to record an image of a person’s fingerprint without the use of ink
- Torchlights lenses
Total Internal Reflection is a special case of reflection which happens when the it goes beyond the critical angle. Total Internal Reflection has many uses in our modern world, one of which is in optical fibers. An optical fiber has two layers: a core made of a material of with a high refractive index, and a second, outer layer with lower refractive index. The light waves carried by an optical fiber are reflected off of the boundary between these two substances, as shown in the diagram of a cross-section of a fiber below. Optical fibers are used in a many different aspects in our modern world. In communication they are used for carrying signals precisely, and at the speed of light. This is much, much faster than the speed of electrons, and therefore faster than electric signals. In medicine, optical fibers are used by operating doctors to view inaccessible places, such as the inside of a lung. Optical fibers are helpful in that they allow the transmission of light to or from places not usually possible. Because they are fibers, they can be bent, allowing light to be bent easily and precisely around many corners, with out the use of more clumsy devices such as mirrors.
Monday, August 1, 2011
flexible, transparent fiber made of very pure glass.
Fibre optics communication permits the transmission over longer distances and at higher bandwidths than other forms of communication.
Fibers are used instead of metal wires because:
1. Signals travel along them with less loss
2. Immune to electromagnetic interference
Total internal reflection is an optical phenomenon that happens when a ray of light strikes a medium boundary at an angle larger than a particular critical angle with respect to the normal to the surface. If the refractive index is lower on the other side of the boundary, no light can pass through and all of the light is reflected. The critical angle is the angle of incidence above which the total internal reflection occurs.
All of the light is reflected.
Question asked: Is this like a mirror?
Answer: No. A mirror only reflects about 90%, the other 10% gets absorbed by the mirror's silver plating or is reflected away from the main image. Since silver oxidizes, a silver mirror can wear out. However, with TIR to reflect light, it will be everlasting.
1) Used in high quality optical devices like periscopes, expensive binoculars or cameras.
2) It is a fundamental part of fiber optic transmission, one of the fastest ways of transmitting information. This is due to the fact that ALL light is reflected using TIR.
Other application is in the use of Optical Fibers whereby the fibers that are made of very pure glass that are coated with layer of material of lower refractive index than that of the fiber. This is important as only when the light or information goes from a higher refractive index into a lower reflective index then it can be reflected, but how is total internal reflection made use? Well it is done so through letting the data or light to enter the optical fiber at a high angle of incidence. This high angle of incidence will be greater than the critical angle, thus causing it to reflected throughout the wire until its destination.
Applications & It's Avantages
- Optical fibers, which are used in endoscopes and telecommunications.
- Rain sensors to control automatic windscreen/windshield wipers.
- Prismatic binoculars (Uses the principle of total internal reflections to get a clearer and an image of a higher magnification as compared to normal binoculars)
- Flashlights glass lenses (Intensifies the light)
A fiber optic is a glass "hair" which is so thin that once light enters one end, it can never strike the inside walls at less than the critical angle. The light undergoes total internal reflection each time it strikes the wall. Only when it reaches the other end is it allowed to exit the fiber.
Fiber optic cables are used to carry telephone and computer communications. Advantages over electrical wired include:
- Fiber optics can carry much more information in a much smaller cable.
- No interference from electromagnet fields result in "clearer" connections.
- No electrical resistance.
- No hazard of electrocution if cable breaks.
A further application is in binoculars and stereo microscopes. A pair of 45-45-90 prisms are arranged so that the incoming light totally reflects off the inside surface of the prisms. This increases the optical path while keeping the size of the instrument relatively compact. And the alignment of the mirrors stays constant.
- Can be faster than speed of light c in vaccuum
- Difficult to obstruct
- Clear and accurate
- If the prism is small enough, less light energy would be lost compared to a mirror
- Rain sensors to control automatic windscreen/windshield wipers.
- Another interesting application of total internal reflection is the spatial filtering of light.
- Prismatic binoculars use the principle of total internal reflections to get a very clear image
- Some multi-touch screens use frustrated total internal reflection in combination with a camera and appropriate software to pick up multiple targets.
- Gonioscopy to view the anatomical angle formed between the eye's cornea and iris.
- Gait analysis instrument, CatWalk, uses frustrated total internal reflection in combination with a high speed camera to capture and analyze footprints of laboratory rodents.
- Fingerprinting devices, which use frustrated total internal reflection in order to record an image of a person's fingerprint without the use of ink.
- Flashlights lenses.