Unit+1+Reflection

=**__Unit 1: Reflection of Light__**=

**Difference between Luminous and Illuminated light sources**

 * Luminous light**-A Luminous light source emits light waves in a result of high temperature.

This is an image of the Sun. The Sun is a luminous light source. It emits light waves. http://www.xet.cn/_game/lib/AsimovGuide_Cosmos/10.htm

This is a light bulb. Light bulb is a luminous light source because it emits light waves. http://www.holymeatballs.org/images/Lightbulb.jpg


 * Illuminated light**-A Illuminated light source reflects light waves produced by an outside source

This is an image of a watch. A watch is an example of an illuminated light source because it reflects light from a luminous light source into our eyes. []

This is an image of the Moon. The Moon is a illuminated light source. It reflects the light waves from the Sun so that people in the Earth and see the Moon. http://www.qicaise.com/photo/197.html

This is an image of a bicycle reflector. A bicycle reflector is a illuminated light source. It reflects the light waves from other light sources so that people can see it. http://www.dkimages.com/discover/Home/Technology/Transportation/Human-powered/Bicycles/Safety/Safety-3.html

Why can we see the moon from the Earth?
The moon orbits around the Earth, and the Sun is off in distance. The moon reflects the light waves from the Sun to the Earth so that the moon can be seen on the Earth. As the moon changes it's position, different fraction of moon will be seen on the Earth because light travels straight and sometimes the light will be blocked. People call it the phases of the Moon.

http://fundyreformed.files.wordpress.com/2006/07/phases-of-moon.jpg

**How shadows are formed?**

 * Opaque**-Substances that cannot see through (eg: book)


 * Transparent**-Substances that can see through (eg: glass)


 * Translucent**-Substances that is half see through (eg: tissue paper)

http://www.le.ac.uk/se/centres/sci/selfstudy/lht2.htm
 * //__Shadows are formed when a opaque object blocks the path of light. For example, if a pencil blocks the path of light, then the pencil creates a shadow. If the source of light moves, so does the shadow.__//**

The fact that shadows can be formed by blocking the light waves shows that light travels in straight lines. If light does not travel in a straight line, shadow would not exist because light can easily curve away from the object.

These are some pictures of Sunlight. As you can see, the Sunlight travels in straight lines. http://img.qj.net/uploads/articles_module/72416/Sunlight_qjpreviewth.jpg

http://www.brighamandwomens.org/publicaffairs/Images/Sunlight.jpg

http://yeinjee.com/discovery/wp-content/uploads/2007/10/sunlight-forest-01.jpg

**Distinguish between plain, concave, and convex mirrors.**
Plain mirrors are straight and have no curvature to their structure; they reflect light at the exact angle from which the light came from (angle of incidence = angle of reflection). http://www.anomet.com/images/50.gif

Concave mirrors curve inwards and reflect light to a focal point in front of the mirror, converging light rays to one point and make whatever is at the focal point clearer and easier to view.

http://www.hazelwood.k12.mo.us/~grichert/optics/intro.html

Convex mirrors are curved outwards; they catch light and reflect it outwards, providing whoever is looking into the mirror a wider view of their surroundings compared to the view given by a plain or concave mirror. http://www.hazelwood.k12.mo.us/~grichert/optics/intro.html

**Outline the laws of reflection.**
1. The incident ray, the reflected ray, and the normal to the reflecting interface all lie in the same plane. 2. The angle of incidence equals the angle of reflection. http://steve.files.wordpress.com/2006/03/reflection%20on%20a%20mirror.jpg

**C Layer, activity 9. Research the every day use of concave and convex mirrors and explain how they work.**
In a concave mirror, light is reflected towards the center of the mirror whereas in convex mirrors, light is reflected away. These different types of mirrors are commonly used to simply make images appear bigger or smaller than they really are. A good example of a common use for concave mirrors is in telescopes, to help make images that are far away appear close by. Also, at theme parks and carnivals one often comes across large curved mirrors that make your body appear warped—these weird images are simply the work of concave and convex mirrors.

Total Internal Reflection:
Total Internal Reflection is the reflection of all of the incident light at the boundary between two mediums. Total Internal Reflection happens when:
 * The light is in the more dense environment and apporaching the less dense environment.
 * The angle of incidence is greater the critical angle (the angle of incidence which provides a 90 degrees angle of refraction).

Here is a diagram of Total Internal Reflection:

http://hyperphysics.phy-astr.gsu.edu/Hbase/phyopt/totint.html

**B Layer, activity 1. Research the use of optical fibers that use the principal of total internal reflection. Choose from an endoscope, binoculars, periscope, or some other optical fiber.**
THE PERISCOPE One might think that the way a periscope works is very complicated, but it is actually very simple. Periscopes are used for people to see images that are above their own eyes—commonly used in submarines to see above the surface of the water from inside the ship. According to the law of reflection, light reflects off a mirror at the same angle that it hit the mirror. In a periscope, light hits the top mirror at a 45-degree angle and reflects away at the same angle, which bounces it down to the bottom mirror. That reflected light hits the second mirror at a 45-degree angle and reflects away at the same angle, right into your eye. The most important thing about a periscope is the angles at which the two mirrors have been positioned. If the angles are not 45 degrees, no image will be visible from the eyepiece. In very technical periscopes used mostly in the navy, optical fibers are used to guide the light along the length of the plastic or glass fibers to provide a very accurate image. Optical fibers use the principle of total internal reflection to guide light rays.

__**THE ENDOSCOPE**__



An endoscope is a device used to see the inside of a human body. An endoscope uses two fiber optic lines. A "light fiber" carries light into the body cavity and an "image fiber" carries the image of the body cavity back to the physician's viewing lens. Endoscopes may be used in conjunction with a camera or video recorder to document images of the inside of the joint or chronicle an endoscopic procedure. New endoscopes have digital capabilities for manipulating and enhancing the video images.

The Image below shows a rigid endoscope used for arthroscopy. The "image fiber" leads from the ocular (eye piece) to the inserted end of the scope. The "light fiber" is below and leads from the light source to the working end of the endoscope.

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The endoscope uses bundles of thin glass fibers to transmit light to and from the organ being viewed. These fibers use the principal of total internal reflection to transmit almost 100 % of the light entering one end to the other end. The way it works is that the light reflects off the glass, creating infinite light throughout the rod.

[|Total internal reflection in optical fibers]