PHYS 222 Spring 2012 Final Exam Closed books, notes, etc. No electronic device except a calculator. NAME: (all questions with equal weight) 1. If the distance between two point charges is tripled, the mutual force between them will be changed by what factor? a. 9.0 b. 3.0 c. 0.33 d. 1/9 2. In x ray machines, electrons are subjected to electric fields as great as 6.0 10 5 N/C. Find an electron s acceleration in this field. (m e = 9.11 10 31 kg, e = 1.6 10 19 C) a. 1.1 10 17 m/s 2 b. 5.4 10 13 m/s 2 c. 4.6 10 10 m/s 2 d. 3.6 10 8 m/s 2 1/14
3. A closed surface contains the following point charges: 6 C, 4 C, 2 C, 4 C. The electric flux coming out of the surface is: a. 16 C/ o. b. 16 C/ o. c. 4 C/ o. d. 4 C/ o. 4. A 9.0 V battery is connected between two parallel metal plates 4.0 mm apart. What is the magnitude of the electric field between the plates? a. 2.3 10 3 N/C b. 9.0 N/C c. 2.3 N/C d. 0.75 10 6 N/C 5. An electron in a cathode ray tube is accelerated through a potential difference of 5.0 kv. What kinetic energy does the electron gain in the process? (e = 1.6 10 19 C) a. 1.6 10 16 J b. 8.0 10 16 J c. 1.6 10 22 J d. 8.0 10 22 J 2/14
6. Find the electrical potential at 0.15 m from a point charge of 6.0 C. (k e = 8.99 10 9 N m 2 /C 2 ) a. 5.4 10 4 V b. 3.6 10 5 V c. 2.4 10 6 V d. 1.2 10 7 V 7. The current in an electron beam in a cathode ray tube is measured to be 70 µa. How many electrons hit the screen in 5.0 s? (e = 1.6 10 19 C) a. 2.2 10 11 electrons b. 8.8 10 13 electrons c. 2.2 10 15 electrons d. 8.8 10 18 electrons 8. An electric toaster requires 1100 W at 110 V. What is the resistance of the heating coil? a. 7.5 b. 9.0 c. 10.0 d. 11.0 3/14
9. Number 10 copper wire (radius = 1.3 mm) is commonly used for electrical installations in homes. What is the voltage drop in 40 m of #10 copper wire if it carries a current of 10 A? (The resistivity of copper is 1.7 10 8 m.) a. 1.3 V b. 0.77 V c. 0.50 V d. 0.13 V 10. Resistors of values 6.0, 4.0, 10.0 and 7.0 are combined as shown. What is the equivalent resistance for this combination? a. 2.3 b. 3.0 c. 10.7 d. 27 4/14
11. Lamps with resistance of 8.0, 12.0, and 24.0 are connected in parallel across a fresh battery. Which lamp dissipates the greatest power? a. the 8.0 lamp b. the 12.0 lamp c. the 24.0 lamp d. All dissipate the same power when in parallel. 12. A hair dryer draws 1 200 W, a curling iron draws 800 W, and an electric light fixture draws 500 W. If all three of these appliances are operating in parallel on a 120 V circuit, what is the total current drawn? a. 19.4 A b. 20.8 A c. 25.4 A d. 36.7 A 13. A stationary positive charge +Q is located in a magnetic field B, which is directed toward the right as indicated. The direction of the magnetic force on Q is: a. toward the right. b. up. c. down. d. There is no magnetic force. 5/14
14. The current in a long wire creates a magnetic field in the region around the wire. How is the strength of the field at distance r from the wire center related to the magnitude of the field? a. field directly proportional to r b. field inversely proportional to r c. field directly proportional to r 2 d. field inversely proportional to r 2 15. Consider two long, straight parallel wires, each carrying a current I. If the currents are flowing in opposite directions: a. the two wires will attract each other. b. the two wires will repel each other. c. the two wires will exert a torque on each other. d. neither wire will exert a force on the other. 16. A uniform 4.5 T magnetic field passes through the plane of a wire loop 0.10 m 2 in area. What flux passes through the loop when the direction of the 4.5 T field is at a 30 angle to the normal of the loop plane? a. 5.0 T m 2 b. 0.52 T m 2 c. 0.39 T m 2 d. 0.225 T m 2 6/14
17. A flat coil of wire consisting of 20 turns, each with an area of 50 cm 2, is positioned perpendicularly to a uniform magnetic field that increases its magnitude at a constant rate from 2.0 T to 6.0 T in 2.0 s. If the coil has a total resistance of 0.40, what is the magnitude of the induced current? a. 70 ma b. 140 ma c. 500 ma d. 800 ma 18. A coil with a self inductance of 0.75 mh experiences a constant current buildup from zero to 10 A in 0.25 s. What is the induced emf during this interval? a. 0.045 V b. 0.030 V c. 0.47 V d. 0.019 V 19. An electromagnetic wave with a peak electric field component of 1.2 10 2 N/C has what associated peak magnetic field value? ( 0 = 8.85 10 12 C 2 /N m 2, 0 = 4 10 7 T m/a and c = 3.00 10 8 m/s) a. 4.0 10 7 T b. 3.6 10 10 T c. 2.5 10 6 T d. 2.8 10 11 T 7/14
20. In order of increasing frequency, which of the following is correct? a. visible, radio, ultraviolet and x ray b. infrared, visible, ultraviolet and gamma c. visible, gamma, ultraviolet and x ray d. infrared, x ray, visible and gamma 21. A radar pulse returns 3.0 10 4 seconds after it is sent out, having been reflected by an object. What is the distance between the radar antenna and the object? (c = 3.00 10 8 m/s) a. 9.0 10 4 m b. 4.5 10 4 m c. 6.0 10 4 m d. 1.0 10 4 m 22. Water has an index of refraction of 1.333. What is the speed of light through it? (c = 3.00 10 8 m/s) a. 4.00 10 8 m/s b. 2.25 10 8 m/s c. 4.46 10 8 m/s d. 1.46 10 8 m/s 8/14
23. A light ray incident on the interface between air and glass can undergo total internal reflection: a. only in the glass. b. only in the air. c. in either the glass or the air. d. in the air only if the index of refraction of the glass is greater than the. 24. A certain kind of glass has n blue = 1.650 for blue light and n red = 1.610 for red light. If a beam of white light (containing all colors) is incident at an angle of 30.0, what is the angle between the red and blue light inside the glass? a. 0.22 b. 0.45 c. 1.90 d. 1.81 25 Which of the following best describes the image from a plane mirror? a. virtual and magnification greater than one b. real and magnification less than one c. virtual and magnification equal to one d. real and magnification equal to one 9/14
26. A woman looking in a makeup mirror sees her face at twice its actual size and right side up. If she is 28.0 cm from the mirror, what is its focal length? a. 18.6 cm b. 44.0 cm c. 48.3 cm d. 56.0 cm 27. Sally places an object 6.0 cm from a thin convex lens along its axis. The lens has a focal length of 9.0 cm. What are the respective values of the image distance and magnification? a. 18 cm and 3.0 b. 18 cm and 3.0 c. 3.0 cm and 0.50 d. 18 cm and 3.0 28. Two narrow slits are 0.025 mm apart. When a laser shines on them, bright fringes form on a screen that is a meter away. These fringes are 3.0 cm apart. What is the separation between the second order bright fringe and the central fringe? a. 8.6 cm b. 6.0 cm c. 5.3 cm d. 2.6 cm 10/14
29. Light of wavelength 610 nm is incident on a slit of width 0.20 mm, and a diffraction pattern is produced on a screen that is 1.5 m from the slit. What is the distance of the second dark fringe from the center of the bright fringe? (1 nm = 10 9 m) a. 0.68 cm b. 0.92 cm c. 1.2 cm d. 1.4 cm 30. A beam of polarized light of intensity I 0 passes through a sheet of ideal polarizing material. The polarization axis of the beam and the transmission axis of the sheet differ by 30. What is the intensity of the emerging light? a. 0.87 I 0 b. 0.75 I 0 c. 0.50 I 0 d. 0.25 I 0 11/14
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