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Ch. 18 - Refraction and Lenses Ch. 18.1- Refraction of light Snell's Law of Refraction ● _______________________:Here n is a constant that depends on the substance, not on the angles, and is called the index of refraction. a. n1sinƟ1=n2sinƟ2 b. sinƟ1/sinƟ2=n Wave model of Refraction ● The wave model of light was developed almost _______________ Snell published his research. ● _________, where v is the speed of light in any medium and A is the wavelength Index of refraction ● The ________________ of a medium is equal to the speed of light in a vacuum divided by the speed of light in the medium a. n=c/v Total Internal Reflection ● As the angle of incidence _________________, the angle of refraction _________________. ● Critical Angle for Total Internal Reflection is sinƟc=n2/n1 ● The sine of the critical angle is equal to the index of refraction of the _______________ medium divided by the index of refraction of the __________________ medium. .Mirages ● As you drive down a road, you see what appears to be the reflection of an oncoming car in a pool of water. The pool, however, disappears as you approach it. The __________ is the result of the Sun heating the road 1 Dispersion of Light ● You learned in Chapter 16 that white light separates into a spectrum of colors when it passes through a glass prism, this phenomenon is called __________________. ● An example is a ________________. Ch. 18.2- Convex and Concave Lenses Types of Lenses ● A lens is a piece of ___________________________, such as glass or plastic, that is used to focus light and form an image. ● ______________ lenses are thicker at the center than at the edges ● ______________ lenses are thinner in the middle than at the edges Convex Lenses and Virtual Images ● When an object is placed at the __________________of a convex lens, the refracted rays will emerge in a parallel beam and no image will be seen. Concave Lenses ● A _______________________ causes all rays to diverge ● All images for a concave lens are _______________. Thus, if an image distance is given as 20 cm from the lens, then you should use di 20 cm Defects of Spherical Lenses ● __________________________ - Making lens surfaces aspherical, such as in cameras, eliminates spherical aberration ● __________________________ - An object viewed through a lens appears to be ringed with color ● __________________________ - is a system of two or more lenses, such as a convex lens with a concave lens, that have different indices of refraction 2 Evaluate the AnswCh. 18.3- Application of Lenses ● ● ● ● Lenses in the Eye ____________________: muscles surrounding the lens contract and relax to change the shape of the lens. a. Relax- ___________ objects b. Contract- __________ objects _____________________ (Myopia): focal length is too short a. ___________ __________ help this problem ______________________(Hyperopia): focal length too long a. __________ _________help this problem Refracting Telescopes Process a. Astronomical objects are so far away that rays are considered parallel b. Parallel rays enter the ___________ ________ _______ which inverts the object c. Image becomes object for convex lens in the _____________ d. Because the focal point of the objective lens is between the ___________ _______ and its ________ ________, the virtual image is now upright and larger than before e. The first image was already inverted, so the final image is still inverted Binoculars ● Process a. Light enters a _________ ____________ _______ which inverts the object b. Light travels through 2 ________ i. Uses ________ ________ ____________to invert image again so it is upright ii. Prism also extends path of light to the eyepiece and separates the objective lenses to improve the 3D view of distant objects Cameras ● 3 Process a. Light enters and passes through ___________ _______ i. Achromatic Lens: refracts the light much like a single convex lens would b. c. d. ii. __________ image on reflex mirror Image reflected upward to prism which inverts image and send light to _____________ Shutter release button ________ mirror Light then travels along straight path to form image on film Microscopes ● 4 Process a. Object is located between two ________ __________ from objective lens b. Real image produced that is ____________ and ___________ between the eyepiece and focal point c. Virtual image produced that is __________ and __________ than image in the objective lens d. Viewer sees inverted and larger image Quiz 1. Which lenses are thicker at the center than at the edges? a. Concave lens b. Achromatic lens c. Convex lens d. Objective lens 2. What is a system of two or more lenses, such as a convex lens with a concave lens, that have different indices of refraction? a. Chromatic aberration b. Spherical lens c. Achromatic lens d. None of the above 3. What a. b. c. d. is it called when images form in front of the retina? Farsightedness Nearsightedness Myopia Both B and C 4. Which devices uses prisms when refracting light? a. Binoculars and camera b. Telescope and binoculars c. Telescope and microscope d. Camera and microscope 5. What is it called when an object viewed through a lens appears to be ringed with color? a. Spherical lens b. Chromatic aberration c. Color blind d. Not enough information 6. Use Snell’s Law. Light travels from air into an optical fiber with an index of refraction of 1.44. If the angle of incidence on the end of the fiber is 22o, find the angle of refraction inside the fiber. Hint: n₁ = 1.00. 5 Test 1. Which type of lens is thinner in the middle than at the edges? a. Concave lens b. Achromatic lens c. Convex lens d. Objective lens 2. How long after Snell published his research did the wave model of light become developed? a. 300 years b. 4 months c. 20 years d. 200 years 3. What is it called when you see what seems to be a pool of water on the road on a hot summer day? a. Hallucination b. Mirage c. Deception d. None of the above 4. Concave lenses cause all rays to ____________? a. Diverge b. Combine c. Switch d. Remain 5. Why are spherical lenses used? a. It makes the image larger b. It is environmentally friendly c. It eliminates spherical aberration d. None of the above 6. When the muscles in your eye relax, what images does the focus on? a. Close objects b. Distant objects c. Invisible objects 7. What part of the eye focuses the light when it initially enters the eye? a. Retina b. Lens c. Cornea 6 8. 9. 10. 11. 7 d. Pupil What type of lenses help fix farsightedness? a. Achromatic lens b. Convex lens c. Concave lens d. Both B and C Which device is used to view astronomical objects? a. Microscope b. Camera c. Binoculars d. Telescope What does the word inverted mean? a. Larger b. Flipped c. Colored d. Smaller What is the critical angle for light traveling from diamond into fiber optic cable, given that the refractive index of diamond is 2.4 and the refractive index of fiber optic cable is 1.6? Use the equation: sinƟc =n2/n1.
