2011 S2-08 Science Blog

Tuesday, August 16, 2011

sound audioexplorer Eugene, Imran and Wenkai

Tuning fork:

Wen Kai:

¡∑®∆π:

Eugene:

Science_Physics-SoundWave of tuning fork and human voice

Human voice

Tuning fork

Physics practical (Celine, Eunice, Kok Yin)

Looks rather small here, but anyway the top left is the low-pitched voice, the top right is the tuning fork, and the bottom one is the high-pitched voice.

Science_Physics-SoundWave of tuning fork and human voice

Picture showing Unknown Tuning Fork

Picture showing Unknown Human Voice

By:

Kang Yan

Ong Bing Jue

Yeo Jun Peng

Sound Graph

Human Voice. By ... Zhang Bo

Tuning Fork

Done by Aaron Sng, Zhang Bo and Ethan Soh

Science_Physics-SoundWave of tuning fork and human voice

Wave 1 : Tuning fork
Wave 2 : Human voice

Done By : Daniel Pei and Seah JIt Sheng.

Science_Physics-SoundWave of tuning fork and human voice

Done By Soe Yan Naung@Norman and Chong Jun Hao

Sound waves- Clarabelle, Kristin, Michelle

Friday, August 5, 2011

Science class next week and additional resources on Refraction

Dear Students,

Please get the following completed.

1. Take 15 mins and complete the following Pre-Quiz on Sound.

Pre-Quiz - Sound

   Remember to key in the following:
   Name / ID (Register Number) /Class
   Password: sound

2. Please follow the following link and install software : AudioXplorer ( must be done before next lesson)

AudioXplorer for Mac OS

You will need this software for the lessons.

Good site on topic Refraction

http://www.cyberphysics.co.uk/topics/light/TIR.htm

On you tube

http://www.youtube.com/user/derekowens

http://www.youtube.com/user/TutorVista#p/search/0/kc2o73FyN3I

Remember to submit your homework.

Thursday, August 4, 2011

Application of total internal reflection

Application

One of the applications of total internal refection is is the optical fibre.

It can be used in fibre-optic communication. Fiber-optic communication is a way of transmitting information from one location to another by sending light through an optical fiber.
Fiber-optic communication (The process):

1. Creating optical signal using a transmitter

2. Relaying the optical signal along the optical fibre

3. Ensuring that the optical signal does not become too weak

4. Receiving the optical signal

5. Converting the optical signal into an electrical signal

Underlying Theory

Total internal reflection

Total internal reflection happens when a ray of light strikes a medium’s surface at an angle larger than the critical angle of the medium. If the refractive index is lower on the other side of the surface, no light can pass through and all the light is reflected. The critical angle is the angle of incidence which the total internal reflection occurs.

Optical fibre

Optical fibre normally consists of a transparent glass core surrounded by a transparent coating with a lower refractive index. Light is kept in the glass core by total internal reflection. This causes the fiber to act as a waveguide.

Advantages

1. Can be used over greater distances due to the low loss, high bandwidth properties
2. It can be used for 2km without the use of a repeater
3. Their light weight and small in size, which makes them ideal for applications where running copper wires would be impractical
4. Due to the fibres being non-conductive, it can be used where electrical isolation is needed
5. The fibres are do not pose a threat to its surroundings, such as in a chemical plant where a spark could cause an explosion.
6. For security reasons, as it is very hard to tap into a fibre cable to read data signals.

Disadvantages

Although there are many advantages there are a few disadvantages that would effect the installation of these cables these are:

1. It is much more costly than other cables to install

2. It is relatively difficult to install

Source:
Application:
http://en.wikipedia.org/wiki/Fiber-optic_communication (Fiber-optic communication - Wikipedia)
Underlying Theory:
http://en.wikipedia.org/wiki/Total_internal_reflection (Total internal reflection - Wikipedia)
http://en.wikipedia.org/wiki/Optical_fiber (Optical Fiber - Wikipedia)
Advantages and Disadvantages:
http://csusap.csu.edu.au/~agarts01/advantages_and_disadvantages.html (Advantages and Disadvantages)
Picture:
http://upload.wikimedia.org/wikipedia/commons/0/02/Optical_fiber_cable.jpg (Optical fiber cable image)

Done by: Tse Tzang, Christian, JingHeng

Refraction Applications By Soe Yan Naung@Norman and Jun Hao

Refraction in the Eye

The fundamental physical phenomenon at work in the eye is that when light crosses a boundary between two media (such as air and the

eye's jelly), part of its energy is reflected, but part passes into the new medium. In the ray model of light, we describe the original ray as splitting into a reflected ray and a transmitted one (the one t

hat gets through the boundary). Of course the reflected ray goes in a direction that is different from that of the original one, according to the rules of reflection we have already studied. More surprisingly --- and this is the crucial point for making your eye focus light --- the transmitted ray is bent somewhat as well. This bending phenomenon is called refraction. The origin of the word is the same as that of the word “fracture,” i.e., the ray is bent or “broken.” (Keep in mind, however, that light rays are not physical objects that can really be “broken.”) Refraction occurs with all waves, not just light waves.

The actual anatomy of the eye, is quite complex, but in essence it is very much like every

other optical device based on refraction. The rays are bent when they pass through the front surface of the eye. Rays that enter farther from the central axis are bent more, with the result that an image is formed on the retina. There is only one slightly novel aspect of the situation. In most human-built optical devices, such as a movie projector, the light is bent as it passes into a lens, bent again as it reemerges, and then reaches a focus beyond the lens. In the eye, however, the “screen” is inside the eye, so the rays are only refracted once, on entering the jelly, and never emerge again.

A common misconception is that the “lens” of the eye is what does the focusing. All the transparent parts of the eye are made of fairly similar stuff, so the dramatic change in medium is when a ray crosses from the air into the eye (at the outside surface of the cornea). This is where nearly all the refraction takes place. The lens medium differs only slightly in its optical properties from the rest of the eye, so very little refraction occurs as light enters and exits the lens. The lens, whose shape is adjusted by muscles attached to it, is only meant for fine-tuning the focus to form images of near or far objects.

Lenses

The ray model of light is very useful in explaining lenses.A lens is a piece of glass or any other transparent material with two curved surfaces, or with one curved and one flat surface. A convex lens is a lens that is thicker in the middle than at its edges. Refraction through such a lens causes parallel light rays to converge (meet) at a point called the principal focus. The lens of your eye is a double convex lens that focuses an image on the retina of the eye.

Sources

http://www.lightandmatter.com/html_books/lm/ch31/ch31.html

http://www.school-for-champions.com/science/optics.htm

Wednesday, August 3, 2011

Application for total Internal Reflection (Eugene and Imran)

1. The cut of the diamond favors total internal reflection. Most rays entering the top of the diamond will internally reflect until they reach the top face of the diamond where they exit. This gives diamonds their bright sparkle. Notice in this animation that a ray entering the top doesn't exit the diamond until it reaches the top surface.
Source: http://regentsprep.org/Regents/physics/phys04/captotint/default.htm

2. Prismatic binoculars use the principle of total internal reflections to get a very clear image

Porro-prism Binoculars

Abbe-Koenig "roof prism" design

Source: http://en.wikipedia.org/wiki/Binoculars#Prism_binoculars

Application of TIR

Bicycle Reflectors

Description of a bicycle reflector

Bicycle reflectors comprise hundreds of cube corner reflectors that look like a honeycomb of hexagonal cells. These cells reflect light that shines on them back to its source, using the principle of total internal reflection.

The walls of the hexagonal cells are angled precisely right to allow TIR to occur. Light travels in a straight line, but the angles in a cube-corner cell are such that a beam of light bounces off one wall, then against another wall, and so on, continually retracing its path. The light exits from the bicycle reflector and refracts as the car's headlights begin to pass beyond the cyclist.

Advantages

-There is no need for the use of energy or electricity to power bicycle reflectors

-The reflector is convenient and user friendly: It is located at the spokes of the wheels, under the seat of a bicycle, or in front. It does not need to be switched on before using.

Disadvantages

-In order for bike reflectors to work effectively, the angle of the light source (car headlights) must shine directly at them. If the headlights are not at a desirable angle, the light rays are refracted outside of the plastic cube-corner cells rather than being reflected inside them.

-In bad weather, (fog or rain) light rays are spread and dispersed, causing the reflectors to become less effective.

-Dirty car headlights and dirty bike reflectors also can impair the function of bike reflectors by blocking the light rays from entering and refracting form the bicycle reflector. (or blocking light rays leaving car headlights).

Photos taken from: http://en.wikipedia.org/wiki/Bicycle_reflector

Information taken from: http://www.ehow.com/how-does_5208844_do-bicycle-reflectors-work_.html

Done by: Ethan Soh, Aaron Sng, Wee Ren Chang

Total Internal Reflection Post for Wen Kai and Jit Sheng

Fibre Optics:

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.

Source:

http://regentsprep.org/Regents/physics/phys04/captotint/default.htm

Rain sensors to control automatic windscreen/windshield wipers.

Gait analysis instrument, CatWalk, uses frustrated total internal reflection in combination with a high speed camera to capture and analyze footprints of laboratory rodents.

http://en.wikipedia.org/wiki/Total_internal_reflection

Members: Lhu Wen Kai, Seah Jit Sheng

Applications of Total Internal Reflection

1. Diamonds sparkling

The brilliance of diamond is due to total internal reflection. The critical angle of light traveling from diamond to air is 24.4 degrees.The ray of light entering the diamond (incident angle) fall at angle greater than 24.4 degrees. This results in multiple, total internal reflections at various angles and remains within the diamond. Hence diamond sparkles.

2. Endoscope

Endoscopes use fiber optics technique. A patient can swallow a tube containing a fine glass fiber through which a doctor can examine the internal stomach parts and hence unnecessary surgeries can be avoided. This is so as the optic fibres uses the principles of total internal reflection to transmit an image that can be inspected visually outside the body.

Advantage of using total internal reflection in endoscopes (or medical purposes):

- No operation will be needed to observe the internal organs of a patients

- Tumors in the body can be killed by using this theory. No operation is needed as the optical fibre rays can be reflected and aimed at the tumor for it to be killed.

Disadvantages of using total internal reflection in endoscopes:

- The equipment needed are expensive

- Total internal reflection might not occur when the angle of incidence is changed, thus causing the equipment unusable.

Done By:

- Kang Yan

- Bing Jue

- Jun Peng

Application of total internal reflection (Eunice, Celine, KokYin)

Total internal reflection is used in Fingerprinting devices, which uses frustrated total internal reflection to record down a person's fingerprint without the use of ink.