Name: Exam #3 D#: Physics 140 Section #: hoose the best answer for each of Questions 1-19 below. Mark your answer on your scantron form using a # pencil. (5.6 pts each) 1. At a certain instant in time, an electromagnetic wave is propagating in the + x direction of the right-handed coordinate system shown in igure 1 below. The magnetic field vector B points in the direction does the electric field vector E point at this instant? z y direction. n what y x ig. 1 a) in the z direction b) in the + z direction c) in the + y direction d) in the y direction e) in the x direction. onsider the diagram of the electromagnetic spectrum shown in igure below. Note that the diagram shows the wavelength λ increasing to the left, as indicated by the horizontal axis given beneath the diagram of the spectrum. A B λ ig. What bands of the spectrum belong in blanks A, B and? a) A = radio waves, B = gamma rays, = infrared b) A = gamma rays, B = infrared, = radio waves c) A = infrared, B = radio waves, = gamma rays d) A = radio waves, B = infrared, = gamma rays e) A = gravity waves, B = higgs boson, = magnetic monopoles 1
Physics 140 3. The handset of a cordless phone transmits electromagnetic waves back to the receiver (the part of the phone that s actually connected to the telephone jack) at 900 MHz (900 megahertz). What is the wavelength of these waves, assuming they propagate with speed c (the speed of light in free space)? a) 0.333 m b) 3.00 m c) 1.00 m d).0 m 9 e) 0 10 m 4. Which of the following statements concerning the spectrum of visible light is (or are) correct? a) The spectrum of visible light represents a large fraction of the total electromagnetic spectrum. b) Visible light waves have wavelengths from about 400 nanometers to about 700 nm. c) The visible spectrum is the part of the total electromagnetic spectrum between infrared and radio waves. d) The visible spectrum includes colors from red to violet, with red having the longest wavelength and violet having the shortest wavelength. e) Both (b.) and (d.). 5. A beam of unpolarized light having intensity 0 = 0 W m strikes the series of two polarizers shown in igure 3. As shown in the figure, each polarizer has its axis at to the vertical. What is the intensity of the light transmitted through this series of polarizers? (This transmitted intensity is shown as in the figure.) 0 = 0 W m 1 a) b) c) d) e) 0 W/m 0.0 W/m 15 W/m 11 W/m ig. 3
Physics 140 6. Vertically polarized light strikes the series of two polarizers shown in igure 4 below. The intensity of the incident light is 0 W/m, as shown in the figure. What is the transmitted intensity? 0 = 0 W m 1 a) b) c) d) e) 0 W/m 0.0 W/m 15 W/m 11 W/m ig. 4 7. Vertically polarized light strikes the series of two polarizers shown in igure 5 below. The intensity of the incident light is 0 W/m, as shown in the figure. What is the transmitted intensity? 0 = 0 W m 1 60 ig. 5 a) b) c) d) e) 0 W/m 0.0 W/m 15 W/m 3.8 W/m 8. Each pulse produced by an argon-fluoride excimer laser used in PRK and LASK ophthalmic surgery lasts only 10.0 nanoseconds, delivering.50 millijoules of energy. f the beam has a diameter of 0.850 mm, what is the average intensity of the beam during each pulse? a) b) c) d) e) 11 5.64 3.67 10 7.31 6 9.7 11 4.41 3
Physics 140 9. A laser beam is reflected by a plane mirror. t is observed that the angle between the incident and reflected beams is 38, as shown in igure 6 below. f the mirror is now rotated so that the angle of incidence increases by 5.0 degrees, what is the new angle between the incident and reflected beams? 38 ig. 6 a) 33 b) 38 c) 43 d) 48 e) 53 10. A small vertical mirror hangs on a wall, 1.40 m above the floor, as shown in igure 7. Sunlight strikes the mirror, and the reflected beam forms a spot on the floor.50 m from the wall, as shown in the figure. Later in the day, you notice that the spot has moved to a point 3.75 m from the wall, as shown. What was the change in the Sun s angle of elevation between your two observations? (That is, what is the angle θ shown in the figure?) θ 1.40 m 3.75 m.50 m ig. 7 a) 8.78 b) 5.0 c) 5.4 d).0 e) 11.7 4
Physics 140 11. Which of the following pictures shows the correct ray diagram for a concave spherical mirror with the object at a distance from the mirror that is greater than the radius of the mirror? ray ray (a.) (b.) ray ray (c.) (d.) ray (e.) 1. onsider the object shown in front of a convex spherical mirror in igure 8 below. The object is closer to the mirror than the focal point is, as shown in the figure. Which of the following sets of statements correctly describes the image? ig. 8 a) image is upright, larger than the object, and virtual b) image is upright, smaller than the object, and virtual c) image is inverted, smaller than the object, and virtual d) image is inverted, smaller than the object, and real e) image is upright, larger than the object, and real 5
Physics 140 13. or the situation shown in igure 8, what is the image distance d i if the object is 1.50 cm from the mirror and the radius of the mirror is 5.00 cm? a) 3.75 cm b) 5.00 cm c) 0.938 cm d) +.14 cm e) +.50 cm 14. n the development of the major results of the reflection of light by spherical mirrors, it was important to restrict our attention to paraxial rays. Which of the following statements concerning paraxial rays is (or are) correct? a) Paraxial rays are rays that are near the principal axis of the mirror. b) Paraxial rays are rays that pass through the center of curvature of the mirror. c) or paraxial rays, there is essentially no spherical aberration. d) Paraxial rays are rays that make angles of 45 with the principal axis of the mirror, and therefore are all reflected parallel to the principal axis of the mirror. e) Both (a.) and (c.). 15. A beam of light in air enters glass (n = 1.50) at an angle of 60.0 relative to the normal, as shown in igure 9 below. ind the angle of refraction. Take the index of refraction of air to be 1.00. ig. 9 a) 35.3 b) 70.0 c) 54.7 d) 81. e) 8.7 6
Physics 140 16. A film of oil, with an index of refraction of 1.48, floats on a pool of water ( n water = 1.33), as shown in igure 10. A beam of light (traveling in air) is incident on the oil at an angle of 60.0 to the vertical, as shown. ind the angle θ the light beam makes with the vertical as it travels through the water. Take the index of refraction of air to be 1.00. a) 5.7 b) 60.0 c) 45.0 d) 40.6 e) 33.3 ig. 10 17. Which of the following pictures shows the correct ray diagram for a converging lens with the object farther away from the lens than the focal point? (a.) (b.) (c.) (d.) (e.) 7
Physics 140 18. Which of the following pictures shows the correct ray diagram for a diverging lens? (a.) (b.) (c.) (d.) (e.) 19. An object 1.0 cm tall is placed 1 cm in front of a diverging lens with a focal length of 7.9 cm. ind the image height h i. a) 4.8 cm b) 0.40 cm c) 3 cm d).4 cm e) 1. cm 8