ch29_egtk

= Reflection and Refraction. =

// 29.1 Reflection //
__//Reflection//__ - When a wave reaches a boundary between 2 media some or all of the wave bounces back into the first medium.
 * if only some of the wave energy is reflected back then it is __//patially reflected//__.
 * If all of the wave energy is reflected then the wave is //__totally reflected__//.
 * Metal objects such as silver and aluminum reflect almost all frequencies of visible light and create almost total reflection (some loss due to friction) which is why they are so shiny

// 29. 2 Law of Reflection //
The angle at which the incidence ray and the normal line intersect is known as the __//angle of incidence//__ The angle at which the reflected ray and the normal line intersect is known as the __//angle of ref l ection //__ Image From: []

These two angles create a concept known the **Law of Reflection:** //angle of incidence = angle of reflection// ^^ this law is only true for straight plane mirrors (meaning that the incident ray, the normal line, and the reflected ray all lie in the same plane

// 29. 3 Mirrors //
When looking into a mirror or into some kind of reflection the image is virtual because the image is not actually there.
 * your eye cannot tell the difference between a real image and a virtual image.
 * an object in a plane mirror is always the same size as the real object.
 * //__Virtual image__// is an image that the rays seem to appear somewhere behind the mirror.

// 29. 4 Diffuse Reflection //
//__Diffuse Reflection__// - when light strikes a rough surface the rays of light reflect off in different directions so there is no reflection. Image From "The Physics Classroom": []
 * an example of diffuse reflection is bouncing a super bouncy ball on a cracked piece of concrete, if the ball hits one edge of the concrete then the ball will bounce at different angle then what you threw it at.

Something like paper or something with no reflection would be a diffuse reflection while a specual reflection is a smoth shiney surface.

**// 29.5 Reflection of Sound //**
Sound reflects well off of smooth surfaces which results in echos. //__Reverberations__// are when the walls in an autitorium are too reflective causing the sound to sound garbled. Concert halls are designed so there are more reflective materials behind and above the stage while the walls are diffuse.
 * If the walls absorb sound then there is no reflection.
 * If the walls are rigid then the sound not be reflected as easily.
 * anything in a room such as people and furniture also reflects sound.
 * However, when the walls are too aborbant, the sound level sounds lower.

// 29.6 Refraction //
__//Refraction//__ - is when a wave goes from one material to another of a different density and the ray reacts to the thickness. Rays bend when the enter a matierial with a different density. Image from "Laser Safety for Laser Operations" __[|www.datasync.com/ ~wizard/Lasers/Lasers.html] // Wave Fronts //__ are continuous portions of waves that are all vibrating the same way at the same time.
 * if a light wave travels from air to a glass then the ray bends twards the normal line.
 * if a light ray travels from glass to air then the ray bends away from the normal line.

// 29.7 Refraction of Sound //
Waves do not need a hard boundry to refract, changes in temperature can make sound refract.
 * sounds will refract up when warn air is below it and cool air is above it.
 * sounds will refract down when there is cool air below it and warm air above it.

29.8 Refraction of Light
Light refracts due to changing from one medium to another and changing temperature and density of a medium. Light refracts twards the normal line when entering a more dense medium and away from the normal line when passing through a less dense medium.


 * Index of refraction: **


 * Snells Law: **

29.9 Atmospheric Refraction
//__Mirage__// occures on hot days when there is a layer of very hot air in contact with the ground, the molecules are further apart in hot air so light travels faster through. the result is hotter air below the wave bending the light wave up causing what appears to be a reflective material that looks like water. In a sunset you see the sun about 5 min after it already sunk below the surface because the light refracts off of the Earth's atmosphere.

29.10 Dispersion in a Prism
Light travels slower than c in a tranparent material depending on the material. Light frequencies are closer to natural frequencies but those frequencies are on the ultra-violot scale. //__Dispersion__// is when light is bent twice at a non parallel boundary like a prism which separates the light into different colors according to thier frequency.

29.11 The Rainbow
A rainbow is formed when the sun is shining in one part of the sky and water dropplets in a cloud or falling is in the other part of the sky.
 * turn your back to the sun and the rainbow and from a plane the rainbow would be completley round.
 * in a rainbow red is bent the least and violot is bent the most.
 * the angle that the refracted light from the drops of rain, are coming to your eyes at about a 42 degree angle.
 * the rainbow moves with you so there is no end to it.

This image came from : [|physics.uwstout.edu/ WX/Notes/ch15notes.htm]

29.12 Total Internal Reflection
The //__Critical Angle__// is the angle at which light shining up through water will no longer make the jump from water to air.
 * at the critical angle light simply reflects off of the surface of the water and reflect back down at the same angle.
 * The critical angle will make the angle of refraction exactly 90 degrees

This image came from : [|www.timbercon.com/ Critical-Angle.html]

When light enters a more dense object from a less dense object at a degree greater than the critical angle //__total internal reflection__// occurs. This is when the beam cannot reflect back into the less dense object. THe only light emerging from the more dense object is difussed.