Refraction Explained PDF

Chapter 12 – Refraction Recall:  Remember that:  Light can travel through a “vacuum” where there are no particles, unlike other energy waves that need particles to help transmit the wave  Light can also travel through certain substances. (a medium) Medium  I...

Chapter 12 – Refraction Recall:  Remember that:  Light can travel through a “vacuum” where there are no particles, unlike other energy waves that need particles to help transmit the wave  Light can also travel through certain substances. (a medium) Medium  In physics, the substance that a wave travels through is known as the MEDIUM (plural: MEDIA)  That means that for a water wave, the medium is water  Sound waves that we hear travel through air particles Did you know? There is no sound in space!?  In science fiction movies like Star Wars, the audience can hear a big explosion when the space ship blows up  In the vacuum of space, in fact, sound, a type of wave, can’t be generated because there are no particles to transmit it  That means that if a space ship explodes, you would hear nothing! Medium Media affect the speed of the wave because the nature of the particles determine how they will respond to the energy that is transmitted by the wave Therefore, waves slow down or speed up depending on the media that they move in Medium – Water Have you tried running in water? What happens to your speed? High resistance = slower movement! Light rays behave in a similar fashion as they pass through mediums of different densities Light ray will either speed up or slow down and this alters its path! (refraction) REFRACTION  Is the bending of light as it travels through different media  As light moves from one media to another, its speed changes, and that is why the path of the light beam changes  Ray diagrams for Refraction (Ex: air and water)  The incident ray is the light traveling through medium #1(air) to the boundary  The refracted ray is the light ray travelling from the boundary through medium 2 (water)  The normal is where the incident ray strikes the second medium and is perpendicular to the boundary between the two media (substances) Ray diagrams for Refraction  The angle of incidence is the angle between the incident ray and the normal.  The angle of refraction is the angle between the refracted ray and the normal. The Rules of Refraction 1. The incident ray, the refracted ray and the normal all lie in the same plane. 2. The incident ray and refracted ray are on opposite sides of the line that separate the media The Rules of Refraction 3) When discussing the refraction of light, media that cause light to slow down are OPTICALLY DENSE 4) The speed of light is the greatest in a vacuum; though air is quite close to that More Rules of Refraction When a light ray is moving: ▫ From a MORE OPTICALLY DENSE MEDIUM to a LESS OPTICALLY DENSE MEDIUM (slow to fast) the light rays bend AWAY from the normal ▫ From a LESS OPTICALLY DENSE MEDIUM to a MORE OPTICALLY DENSE MEDIUM (fast to slow) the light rays bend TOWARDS the normal Think “FAST”  Use this helpful acronym to remember the properties of refraction  F A: Faster – Away (from normal)  S T: Slower – Toward (the normal)  AIR: MED 1 NORMAL INCIDENT RAY REFRACTED RAY PARTIALLY REFLECTED RAY BOUNDARY GLASS: MED 2  GLASS: MED 1 INCIDENT RAY PARTIALLY REFLECTED RAY AIR: MED 2 NORMAL BOUNDARY REFRACTED RAY Partial reflection and refraction  Anytime a wave tries to cross a boundary, the change in medium kind of acts like a barrier  Some of the energy of the wave will bounce off the boundary  This creates the partially reflected ray that you see in the picture  AIR: MED 1 NORMAL INCIDENT RAY REFRACTED RAY PARTIALLY REFLECTED RAY INCIDENT RAY BOUNDARY GLASS: MED 2 AIR: MED 2 GLASS: MED 1 NORMAL BOUNDARY REFRACTED RAY Refraction and Perception bent straw explained The light rays exit the water and bend away from the normal and towards our eyes Refraction and Perception  The light rays coming from the object have been bent away from the original straight line path that they should have taken from the object to your eyes  This fools your eyes into thinking that you are looking at something that is in a different location, or is of a different size Video: Refraction Explained INDEX OF REFRACTION Chapter 12.4  Index of Refraction  The speed of light is different for each medium but is always less than the speed of light in a vacuum.  The change in the speed of light at the boundary of a substance causes refraction.  The speed of light in a medium is a distinctive optical property of that medium. Index of Refraction  The index of refraction for a medium is defined as the ratio of the speed of light in a vacuum to the speed of light in that medium. C is a known value and always remain the same C = 3.00x10^8  Indices of Refraction  1. All substances are transparent or translucent. Opaque substances cannot refract light.  2. Denser substances tend to have a higher index of refraction. (exception - oil and water!!)  Examples Light travels through a mystery material with a speed of 2.5x10^8. What is the index of refraction of this material? Use GRASP. G: V = 2.5x10^8 C = 3.0x10^8 S: R: n n = 1.2 A:  Diamond has an index of refraction of 2.42 – how fast does light travel through a diamond? G: n = 2.42 S: c = 3.00 × 108 m/s R: V Divide only the first two values and carry the 10^8 to the final answer 3.0 / 2.42 = 1.25 A: Add the x10^8 V = 1.25x10^8 Rearrange to solve for V! 1) Multiply both sides by V 2) Divide both sides by n  Lets try drawing some examples AIR 1) Identify the “boundary” 2) Identify the normal to the boundary WATER 3) Draw the incident ray 4) Examine the medium (more or less optically dense?) 5) Draw the refracted ray based on #4 (FAST) 6) Draw refracted ray exiting medium (repeat the steps) You can see that the angle of incidence is larger than the angle of refraction when the second medium is more optically dense You can see that the angle of incidence is smaller than the angle of refraction when the second medium is less optically dense Worksheet time!  Lets do Example b) together Lets take it up: #2  Air/vacuum =  Olive oil =  Glass =  Zicron =  Diamond = Lets take it up: #3  Air to ice =  Ice to air =  Ait to diamond =  Diamond to air =  Olive glass =  Glass olive oil = Lets take it up: #4