Midterm 3 - University of Michigan

University of MichiganPhysics 126 Winter 2010Name______________Section_______Exam 3 Form 1Instructions:Please keep booklet closed until instructed.You may use a new notecard on two sides of a 3x5 index card,plus your notecards from Exams 1 & 2.Answer questions on the scantron sheet by blackening the dotThe time for the exam is 90 minutes.Useful Physical Constants:eεkμ= 1.602×10−19C12 2 20= 8.85× 10−C /(N⋅m )= 1/(4 πε9 2 20) = 8.99× 10 N⋅m /C70= 4π× 10−T⋅m/A8c = 2.997×10 m/sh = 6.626×10-34J-s-15= 4.14×10 eV-sR = 1.097×107 m-1m-31e = 9.11×10 kgp-27m = 1.67×10 kgg = 9.8 m/s2−4T× 10-19J1 G = 101 eV = 1.6Discussion Sections# time leader3 8 am Merlin4 9 am Merlin5 10 am Merlin6 8 am Lau8 10 am Riles12 11 am Riles13 12 noon Riles14 1 pm Adams16 2 pm Adams17 3pm Adams1

1. When ultraviolet photons with a wavelength of 3.45 × 10 –7 m are directed at the surfaceof an unknown metal in vacuum, electrons with a maximum kinetic energy of 1.52 eVare emitted from the surface. What is the work function of the metal?A) 2.08 eVB) 3.60 eVC) 1.98 eVD) 2.59 eVE) 3.11 eV2. The headlights of a car are 1.6 m apart. The pupil of the eye of the observer has adiameter of 4.0 mm and a refractive index of 1.4. What is the maximum distance fromthe observer that the two headlights can be distinguished?A) 9.1 kmB) 13 kmC) 16 kmD) 11 kmE) 8.0 km3. In a cinema, a picture 2.5 cm wide on the film is projected to an image 3.0 m wide on ascreen which is 18 m away. The focal length of the lens is about:A) 7.5 cmB) 10 cmC) 12.5 cmD) 15 cmE) 20 cm4. Electromagnetic radiation with a wavelength of 5.7 × 10 –12 m is incident on stationaryelectrons. Radiation that has a wavelength of 6.577 × 10 –12 m is detected at a scatteringangle of :A) 10°B) 121°C) 40°D) 50°E) 69°5. A fish swims 2.00 m below the surface of a pond. At what apparent depth does the fishappear to swim if viewed from directly above? The index of refraction of water is 1.33.A) 2.66 mB) 3.00 mC) 1.50 mD) 2.00 mE) 1.33 m3

6. A laser emits a 5.0 × 10 3 -J pulse of light that has a wavelength of 480 nm. Determinethe number of photons in the pulse.A) 3.1 × 10 22B) 1.2 × 10 22C) 8.1 × 10 24D) 2.5 × 10 19E) 5.2 × 10 167. In a scene from a movie, a nearsighted character removes his eyeglasses and uses themto focus the nearly parallel rays of the sun to start a fire. What is physically wrong withthis scene?A) Sunlight cannot be used to start a fire.B) The eyeglasses have diverging lenses and cannot be used to focus parallel rays.C) Parallel rays cannot be focused.D) The eyeglasses have converging lenses and cannot be used to focus parallel rays.E) A fire can only be started if the image is virtual.8. Determine the wavelength of light emitted when electrons in a sample of hydrogenatoms make transitions from the n = 7 level to the n = 4 level.A) 3450 nmB) 2170 nmC) 950 nmD) 7300 nmE) 5910 nm9. In a Young's double-slit experiment, light of wavelength 500 nm illuminates two slitswhich are separated by 1 mm. The separation between adjacent bright fringes on ascreen 5 m from the slits is:A) 0.50 cmB) 1.0 cmC) 0.25 cmD) 0.10 cmE) none of the above4

10. Two rockets, A and B, travel toward each other with speeds 0.5c relative to an inertialobserver. Determine the speed of rocket A relative to rocket B.A) 0.6cB) cC) 0.8cD) 0.4cE) 0.2c11. A light ray is traveling in a diamond (n = 2.419). If the ray approaches the diamond-airinterface, what is the minimum angle of incidence that will result in all of the lightreflected back into the diamond? The index of refraction for air is 1.000.A) 65.58°B) 77.54°C) 32.46°D) 54.25°E) 24.42°12. In an experiment to determine the speed and position of an electron (m = 9.11 × 10 –31kg), three researchers claim to have measured the position of the electron to within ± 10 –9 m. They reported the following values for the speed of the electron:Researcher A 3 × 10 6 ± 2 × 10 4 m/sResearcher B 4 × 10 8 ± 2 × 10 7 m/sResearcher C 2 × 10 7 ± 5 × 10 5 m/sWhich of these measurements violates one or more basic laws of modern physics?A) A onlyB) B onlyC) A and BD) B and CE) A, B, and C5

13. A convex mirror has a radius of curvature of 0.50 m. Where must an object be placed infront of the mirror such that the image is formed 0.15 m behind the mirror?A) 0.57 mB) 0.093 mC) 0.19 mD) 0.375 mE) 0.77 m14. A man stands with his nose 8 cm from a concave shaving mirror of radius 32 cm. Thedistance from the mirror to the image of his nose is:A) 8 cmB) 12 cmC) 16 cmD) 24 cmE) 32 cm15. A 4.0 × 10 2 -nm thick film of kerosene (n = 1.2) is floating on water (n=1.33). Whitelight is normally incident on the film. What is the visible wavelength in air that has amaximum intensity after the light is reflected? Note: the visible wavelength range is380 nm to 750 nm.A) 420 nmB) 480 nmC) 530 nmD) 601 nmE) 380 nm16. In the year 2100, an astronaut wears an antique, but accurate, “quartz" wristwatch on ajourney at a speed of 2.0 × 10 8 m/s. According to mission control in Houston, the triplasts 14 hours. How long was the trip as measured on the watch?A) 8.9 hrB) 10.4 hrC) 18.8 hrD) 6.7 hrE) 16.1 hr17. A scuba diver shines a flashlight from beneath the surface of water (n = 1.33) such thatthe light strikes the water-air boundary with an angle of incidence of 37°. At what angleis the beam refracted?A) 65°B) 48°C) 90°D) 53°E) 31°6

18. A beam of electrons is incident on a single slit that has a width of 1.00 × 10 –6 m and adiffraction pattern is observed on a screen located 15.0 m from the slit. The momentumof an individual electron in the beam is 5.91 × 10 –24 kg ⋅ m/s. What is the width of thecentral maximum fringe?A) 7.50 × 10 –3 mB) 6.67 × 10 –4 mC) 5.87 × 10 –5 mD) 1.33 × 10 –4 mE) 3.37 × 10 –3 m19. How much energy would be released if 1.0 g of material were completely converted intoenergy?A) 9 × 10 9 JB) 9 × 10 16 JC) 9 × 10 8 JD) 9 × 10 11 JE) 9 × 10 13 J20. Without his contact lenses, Mr. Chong can focus from 0.80 m to infinity. Whatrefractive power of the lenses does he require for normal reading (0.25 m from theeyes)?A) 5.25 dioptersB) 1.25 dioptersC) –5.25 dioptersD) 4.00 dioptersE) 2.75 diopters7

Answer Key Exam 3 Form 11. A2. A3. D4. D5. C6. B7. B8. B9. C10. C11. E12. C13. D14. C15. B16. B17. D18. E19. E20. E8