Refraction of Light PDF

CHAPTER THE REFRACTION OF LIGHT 12 KEY QUESTION: How does light behave as it travels from one medium into another? Key Concepts Light changes direction predictably as it travels through different transparent media. Light bends towa...

CHAPTER THE REFRACTION OF LIGHT 12 KEY QUESTION: How does light behave as it travels from one medium into another? Key Concepts Light changes direction predictably as it travels through different transparent media. Light bends toward the normal when it slows down in a medium with a higher index of refraction. Total internal reflection may occur when an incident ray is aimed at a medium with a lower index of refraction. Many optical devices make use of the refraction and reflection of light. The refraction and reflection of light can be used to explain natural phenomena. Understanding the behaviour of light is key to many careers.  CHAPTER ENGAGE IN SCIENCE From Earth to the Moon and Back! 12 The following conversation was recorded on July 21, 1969. Armstrong: The top of that next little ridge there. Wouldn’t that be a pretty good place? Aldrin: All right. Should I put the LR-cubed right about here? Armstrong: All right. Aldrin: I’m going to have to get on the other side of this rock here. Armstrong: I would go right around that crater to the left there. Isn’t that a level spot there? Aldrin: I think this right here is just as level. There are two remarkable things about this conversation. The first is that this conversation took place on the surface of the Moon in a location called the Sea of Tranquility. The second remarkable thing is that they were talking about the placement of a special device called the “LR-cubed.”  LIGHT TRAVELLING THROUGH 12.1 TWO MATERIALS When light strikes a translucent or transparent material, refraction it bends, or refracts. The refraction of light is due to its speed changing as it passes from one material into another. Depending on the material, light either speeds up or slows down. Light cannot travel any faster than 3.0 ´ 108 m/s, which is the speed of light in a vacuum.  RULES FOR REFRACTION 12.1 There are three predictable results when light refracts: angle of refraction – The incident ray, the refracted ray, and the normal all lie in the same plane. – Light bends toward the normal if it travels more slowly in the second medium than in the first. – Light bends away from the normal if it travels faster in the second medium than in the first. refracted ray angle of refraction angle of incident ray incidence  12.2 THE PATH OF LIGHT From Air into Acrylic In this activity, you will explore the path of light as it travels through two transparent media. Purpose To explore the path of light as it travels from one transparent medium into another. Equipment and Materials ray box with single slit semicircular acrylic block polar graph paper (or ruler and protractor) When unplugging the ray box, do not pull the electric cord. Pull the plug itself.  12.3 THE REFRACTION OF LIGHT THROUGH DIFFERENT MEDIA In Activity 12.2, you examined the refraction of light when it travelled from air into a semicircular acrylic block. You also learned that light bends toward the normal when it slows down in a medium. What happens when light goes through different media? What can you learn by examining and comparing refraction in different media? Purpose To explore how the angle of refraction changes in different media. Equipment and Materials semicircular plastic dish polar graph paper (or ruler and protractor) ray box with single slit water When unplugging the ray box, do not pull the vegetable oil electric cord. Pull the plug itself. glycerol (optional) dish detergent (to clean vegetable oil residue on plastic dish)  MEASURING REFRACTION 12.4 The amount of refraction in a material can be determined index of refraction using the index of refraction. The index of refraction can be used to calculate the speed of light in that material. Index of Material Refraction (n) The greater the index of refraction, the more the speed of light will slow down in that material.  SPECIAL CASES OF REFRACTION: 12.5 Partial Reflection and Refraction When light travels through two translucent or transparent materials, some light refracts, but some light reflects off the surface of the second material. The refraction and reflection happen at the same time. This situation is called partial reflection and refraction. An example of partial reflection and refraction occurs when you look through a transparent window or at the surface of a pond. reflected ray refracted ray incident ray  SPECIAL CASES OF REFRACTION: 12.5 Total Internal Reflection When light speeds up as it enters another material, the critical angle angle of refraction is greater than the angle of incidence. total internal reflection As the angle of incidence increases, the refracted ray eventually travels along the boundary of the two materials. – When this happens, the angle of incidence is called the critical angle and the angle of refraction is 90°. If the angle of incidence is increased even more, all the light gets reflected back into the first medium. – This situation is called total internal reflection. Ray 1 Ray 2 Ray 3  APPLICATION OF 12.5 TOTAL INTERNAL REFLECTION Many technologies and devices involve the total internal retro-reflector reflection of light.  12.6 MEASURING THE CRITICAL ANGLE OF VARIOUS MEDIA Light bends away from the normal when it travels more slowly in the first medium than in the second. Total internal reflection in the first medium will occur when light has an angle of incidence greater than the critical angle for that medium. Purpose To explore the critical angle for various media. Equipment and Materials ray box with single slit semicircular acrylic block semicircular plastic dish When unplugging the ray box, do not pull the water electric cord. Pull the plug itself. glycerol vegetable oil polar graph paper (or ruler and protractor) dish detergent (to clean vegetable oil residue on plastic dish)  HIDING IN PLAIN SIGHT The Invisibility Cloak Many works of entertainment have used invisibility as a plot device, from Wells’s 1897 novel The Invisible Man to Harry Potter’s invisibility cloak. But is it just fiction, or is there something more to the idea? Scientists are now working with special materials called metamaterials, which have extraordinary properties that are not found in natural materials; they respond to electromagnetic waves in entirely new ways. These new materials have a negative index of refraction. A negative index of refraction means that the material still refracts light, but the refracted ray is on the same side of the normal in the second material  REFRACTION APPLIED TO 12.7 NATURAL PHENOMENA Refraction can be used to explain many natural phenomena. apparent depth mirage Phenomenon Light Description of Explanation dispersion Concept What You See Using Light Involved Rays apparent depth refraction Objects underwater appear to be at a shallower depth than they really are. flattened Sun refraction During sunset, the Sun near the horizon appears to be flattened.  REFRACTION APPLIED TO 12.7 NATURAL PHENOMENA Refraction can be used to explain many natural phenomena. apparent depth mirage Phenomenon Light Description of Explanation dispersion Concept What You See Using Light Involved Rays mirage refraction On a very hot day, a pool of water on the road appears to be in front of a motorist. rainbow refraction, When water dispersion droplets are in Earth’s atmosphere and the Sun is behind you, you see all the colours in the visible spectrum.  CHAPTER LOOKING BACK 12 KEY CONCEPTS SUMMARY LOOKING BACK Light changes direction predictably as it travels through different transparent media. – The speed of light depends on the medium that it is passing through. – Light bends toward the normal when it slows down in a medium and away from the normal when it speeds up in a medium. – Light can undergo partial reflection and refraction at the same time at a surface.  CHAPTER LOOKING BACK 12 KEY CONCEPTS SUMMARY LOOKING BACK Light bends toward the normal when it slows down in a medium with a higher 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; it is a dimensionless quantity. – Mathematically, the index of refraction is defined as.  CHAPTER LOOKING BACK 12 KEY CONCEPTS SUMMARY LOOKING BACK Total internal reflection may occur when an incident ray is aimed at a medium with a lower index of refraction. – The critical angle is the angle of incidence for which the angle of refraction is 90°; this occurs only when light passes from one medium into another with a lower index of refraction. – Total internal reflection occurs if the angle of incidence is greater that the critical angle.  CHAPTER LOOKING BACK 12 KEY CONCEPTS SUMMARY LOOKING BACK Many optical devices make use of the refraction and reflection of light. – Optical devices such as periscopes, binoculars, retro-reflectors, and fibre- optic cables make use of total internal reflection. – A triangular prism, depending on its orientation, can change the direction of light by 90° (one total internal reflection) or 180° (two total internal reflections).  CHAPTER LOOKING BACK 12 KEY CONCEPTS SUMMARY LOOKING BACK The refraction and reflection of light can be used to explain natural phenomena. – Objects in water appear to be at a shallower depth (an apparent depth) than they really are as a result of the refraction of light. – Shimmering and mirages are the result of refraction and total internal reflection in layers of air of different temperature. – A rainbow is caused by refraction and partial internal reflection of sunlight in water droplets in Earth’s atmosphere.  CHAPTER LOOKING BACK 12 KEY CONCEPTS SUMMARY LOOKING BACK Understanding the behaviour of light is key to many careers. – Jewellers apply the total internal reflection of light in precious and semiprecious stones to create very appealing designs. – Manufacturers of glass prisms apply the refraction and total internal reflection of light to manufacture prisms that can accurately change the direction of light by 90° or 180°.  CHAPTER QUIZ 12 MULTIPLE CHOICE For each question, select the best answer from the four alternatives. 1. When light travels from air into glass, what happens to the light? (a) It speeds up. (b) It bends away from the normal. (c) It slows down. (d) There is no change to the direction of light. 2. Which optical devices do not involve the refraction of light? (a) periscopes (b) retro-reflectors (c) binoculars (d) plane mirrors  CHAPTER QUIZ 12 FILL IN THE BLANKS Copy each of the following statements into a notebook. Fill in the blanks with a term from the box below that correctly completes the sentence. mirages; second medium; critical angle; the flattening of the Sun; refraction; angle of refraction; first medium; dispersion 3. When the __________ is equal to 90°, the angle of incidence is called the __________. This situation happens when light travels more slowly in the __________ than in the __________. 4. __________ and __________ are two natural phenomena that involve __________. Rainbows also involve __________.  CHAPTER QUIZ 12 SHORT ANSWER 5. Copy the diagram below. Draw the path(s) of light after light strikes the window. Label each light ray.  CHAPTER QUIZ ANSWERS 12 MULTIPLE CHOICE 1. When light travels from air into glass, what happens to the light? (a) It speeds up. (b) It bends away from the normal. (c) It slows down. (d) There is no change to the direction of light. 2. Which optical devices do not involve the refraction of light? (a) periscopes (b) retro-reflectors (c) binoculars (d) plane mirrors  CHAPTER QUIZ ANSWERS 12 FILL IN THE BLANKS 3. When the angle of refraction is equal to 90°, the angle of incidence is called the critical angle. This situation happens when light travels more slowly in the first medium than in the second medium. 4. Mirages and the flattening of the Sun are two natural phenomena that involve refraction. Rainbows also involve dispersion.  CHAPTER QUIZ ANSWERS 12 SHORT ANSWER 5. reflected ray refracted ray incident ray