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Chapter 15: Refraction and Lenses Lecture Questions: 1) What is refraction and when does it occur? When a wave is refracted what happens to its frequency, wavelength and speed? Which way will a ray bend when going from a fast to a slow medium? How about when going from a slow to fast medium? Write Snell’s law and define each of the variables. Define the index of refraction. Write Snell’s law using the index of refraction. 2) How does the speed of sound vary with the density and temperature of a medium? How does the speed of light vary with the density and temperature of a medium? 3) Draw a picture showing how we can still receive light from the Sun even after it sets over the horizon. Explain the formation of the pumpkin sun phenomenon. 4) Draw a picture showing how light is bent in a light mirage. Indicate the areas of high and low temperature. 5) Draw a picture showing a sound mirage. Again show the areas of high and low temperature air. 6) What two variables determine the fate of a wave when it hits a boundary? Under what conditions is a wave absorbed? Under what conditions is a wave reflected and refracted? Under what conditions is a wave reflected only? 7) Define the critical angle of a substance? What is the refracted angle when the incident angle equals the critical angle? 8) A Native American sees a fish in the water. In order to spear the fish where should he aim? What does the fish see when it looks up towards the surface of the water? 9) Define total internal reflection (TIR). Do objects that experience TIR have large or small critical angles? Give some examples of TIR. 10) What is dispersion and when does it occur? Draw a picture explaining how a Moon halo forms. Draw a picture showing how a rainbow forms and where you need to stand to see one. How does a secondary rainbow form and how is it different than a primary bow? Why are rainbows, bow shaped? 11) What is the shape of a convex lens and what does it cause parallel light rays to do? What is the shape of a concave lens and what does it cause parallel light rays to do? 12) Define the terms center of curvature, principal axis, focal point object and image for a lens. Which side of a lens is considered the positive side and which the negative side. Write the distance and magnification equations for a lens. 13) What are the principal rays for a converging lens? Draw ray diagrams for objects that are: a) within one focal length of the lens b) between one and two focal lengths of the lens; c) more than two focal lengths from the lens. State what type of image is formed in each case. 14) What are the principal rays for a diverging lens? Draw a ray diagrams for a diverging lens. What type of image does a diverging lens form? 15) What are chromatic and spherical aberrations of a lens? What are some solutions to these problems? 16) What type of lens is used in a camera? Compare the light rays a camera receives from a near and far object? How is a camera able to focus on near and far objects? How is the diaphragm of the camera used to focus on near and far objects? 17) What type of lenses is used for a microscope and how are they placed? What type of lenses is used for a refracting telescope and how are they placed? What type of image does each of these instruments produce? How do the lenses for a microscope and telescope differ? What modification is made to these instruments to allow photography? 18) To what optical instrument is the human eye the closest in function? What is wrong with the vision of someone who is near sighted, what is the anatomical cause of this problem and what type of lens is used to correct it? What is wrong with the vision of someone who is near sighted, what is the anatomical cause of this problem and what type of lens is used to correct it? What is wrong with the vision of someone who is far sighted, what is the anatomical cause of this problem and what type of lens is used to correct it? What is astigmatism and how is it corrected? Problems: 1) Find the angle of refraction for a ray of light that enters a bucket of water from air at an angle of 25.0 degrees to the normal. The indices of refraction for water and air are 1.333 and 1.000 respectively. 2) A ray of light of vacuum wavelength 550 nm traveling in air enters a slab of transparent material. The incoming ray makes an angle of 40.0 degrees with the normal, and the refracted ray makes an angle of 26.0 degrees with the normal. Find the index of refraction for the transparent material assuming the index of refraction for air is 1.00. 3) For an incoming ray of light of vacuum wavelength 589 nm, fill in the unknown values for the following table. From (medium) To (medium) I r Flint glass Crown glass 25.0 degrees (n=1.66) (n=1.52) Air (n=1.00) 14.5 degrees 9.80 degrees Air (n=1.00) Diamond 12.5 degrees (n=2.419) 4) Find the critical angle for light traveling from glycerine (n=1.473) into air. 5) Calculate the critical angle for light traveling from glycerine into water. 6) Find the critical angle for light traveling from ice (n=1.309) into air. 7) Which has a smaller critical angle in air, diamond (n=2.419) or cubic zirconia (n=2.20)? Show your work. 8) An object is placed 20.0 cm in front of a converging lens of focal length 10.0 cm. Find the image distance and describe the image. 9) Sherlock Holmes examines a clue by holding his magnifying glass (with a focal length of 15.0 cm) 10.0 cm away from an object. Find the image distance and describe the image formed. 10) An object placed 20.0 cm in front of a diverging lens of focal length 10.0 cm. Find the image distance and describe the image. 11) Fill in the missing values for the following table. F P Q Converging Lens 6.0 cm Diverging lens -6.0 cm Schedule: Day Monday Tuesday Wednesday Thursday Friday Monday Tuesday Wednesday Thursday Friday 2.0 cm 5.0 cm M 7.0 cm 4.0 cm 5.0 cm Class Assignment Lecture: Refraction (Q 1-5) Lecture: Critical Angle and Dispersion (Q 6-10) Problem Solving (P 1-7) Homework Review and NTQ Lab: Lens Stations Lecture: Lenses (Q 11-15) Lecture: Optical Phenomena (Q 16-18) Problem Solving (P 8-11) Homework Review and NTQ Chapter 15 Quiz 0.50 Homework Due None None None Chp. 15 Qs 1-16, 37-51 None None None None Chp. 15 Qs. 17-36 Notebook