Physics 202 Final Exam Dec 20nd, 2011

Transcription

1 Physics 202 Final Exam Dec 20nd, 2011 Name: Student ID: Section: TA (please circle): Daniel Crow Scott Douglas Yutao Gong Taylor Klaus Aaron Levine Andrew Loveridge Jason Milhone Hojin Yoo Instructions: 1. Don't forget to write down your name, student ID#, and section number. You need to do this on this page of your test book and on your Scantron sheet as well, where you should fill in your student ID number under Identification Number and your three digit section number starting with "3" under special codes. 2. Answer all multiple questions in this test book by indicating the best answer among choices. You must do this both on your test book and on your Scantron sheet. Follow instructions on the Scantron sheet on how to mark valid answers. 3. When you finish, you need to turn in both this test book and the Scantron sheet. 4. Use the blank sides of question pages as additional draft spaces. An extra bank sheet is provided at the end of the test book. 5. Only one answer is allowed per problem/question/ All problems have equal weight. Constants: k e = 8.99 x 10 9 Nm 2 /C 2 electric vacuum permittivity ε 0 = 8.85x10-12 C 2 /(Nm 2 ) magnetic vacuum permeability µ 0 = 4πx10-7 Tm/A Area of a sphere: 4πr 2, Volume of a sphere: (4/3)πr 3 Speed of light: c = 3.00x10 8 m/s Page 1

2 1. Three charges are located at m intervals along a horizontal line: a charge of 3.0 C on the left, 2.0 C in the middle, and 1.0 C on the right. What is the electric field horizontal line halfway between the 3.0 C and 2.0 C charges? A) N/C to the left B) N/C to the right C) N/C to the left D) N/C to the right E) N/C to the left on the 2. An electric dipole composed of positive and negative 25nC charges seperated by 1.0mm makes an angle of 65 with a uniform electric field the magnitude of the torque on the dipole? A) Nm B) Nm C) Nm D) Nm E) Nm of magnitude N/C. What is 3. A solid sphere of radius a is concentric with a hollow sphere of radius b, where b > a. If the solid sphere has a uniform charge distribution totaling +Q and the hollow sphere a charge of Q, the electric field at radius r, where r < a, is which of the following, in terms of k = (4π 0 ) 1? A) kq/r 2 B) kqr/a 3 C) kq/a 2 D) kq/b 2 E) zero Page 2

3 Use the following to answer question 4. An infinite slab of thickness 2d lies in the xz plane. The slab has a uniform volume charge density ρ. 4. The electric at y = b where b > d is A) 2πkρ/d B) 4πkρ/d 2 C) 4πkρd D) 2πkρd E) 4πkρ/d 5. A lithium nucleus with a charge of 3( ) C and a mass of 7( ) kg, and an alpha particle with a charge of 2( ) C and a mass of 4( ) kg, are at rest. They could be accelerated to the same kinetic energy by A) accelerating them through the same electrical potential difference. B) accelerating the alpha particle through V volts and the lithium nucleus through 2V/3 volts. C) accelerating the alpha particle through V volts and the lithium nucleus through 7V/4 volts. D) accelerating the alpha particle through V volts and the lithium nucleus through 7V/6 volts. E) none of these procedures Page 3

4 6. The capacitance of a parallel-plate capacitor is 24 µf when the plates are separated by a material of dielectric constant 2.0. If this material is removed, leaving air between the plates, and the separation between the plates is tripled, the capacitance is A) unchanged B) 16 µf C) 36 µf D) 0.14 mf E) 4.0 µf 7. You connect resistors of 2 Ω, 3 Ω, and 6 Ω in parallel across a battery. The current through the 6-Ω resistor is 3 A. The power dissipated in the 3-Ω resistor is approximately: (solve to two significant figures) A) 0.24 kw B) 0.11 kw C) 0.36 kw D) 0.54 kw E) 0.86 kw 8. Which of the following statements is false? A) Electric field lines due to an electric dipole and magnetic field lines due a magnetic dipole have similar configuration. B) Electric field starts from a positive charge and ends at a negative charge. C) Magnetic field starts at the north pole and ends at the south pole. D) Magnetic poles always occur in pairs. E) Magnetic fields result from the flow of charges. Page 4

5 9. A rectangular loop of wire (0.10 m by 0.20 m) carries a current of 5.0 A in a counterclockwise direction. The loop is oriented as shown in a uniform magnetic field of 1.5 T. The magnitude of the force acting on the upper 0.10-m side of the loop is A) 1.5 N B) 0.75 N C) 0.50 N D) 0.65 N E) zero 10. At great axial distances x from a small current-carrying loop the magnetic field varies as: (the x axis is perpendicular to the plane of the loop) A) x 2 B) x 3 C) x 2 D) x 3 E) x Two long, straight parallel wires 7.6 cm apart carry currents of equal magnitude I. They attract each other with a force per unit length of 4.3 nn/m. The current I is approximately A) 1.6 ma B) 40 ma C) 37 ma D) 59 ma E) 4.0 ma Page 5

6 12. A 3.0-cm by 5.0-cm rectangular coil has 100 turns. Its axis makes an angle of 55 with a uniform magnetic field of 0.35 T. It requires 0.33 s to turn the coil until its plane is perpendicular to the magnetic field. What is the (average) magnitude of the induced EMF? A) 0.16 V B) 0.13 V C) 91 mv D) 68 mv E) 29 mv Use the following to answer question 13. The battery has a voltage V = 6 V, the inductance of the inductor L = 12 mh and the capacitance of the capacitor C = 8 µf. Assume that the inductor and the wires have zero resistance. 13. The switch S was at position a for a long time when it is switched to b. What is the charge on the capacitor at t = ms after the circuit is switched to b? A) 0.75 µc B) 1.33 µc C) 48 µc D) 72 µc E) zero 14. An electromagnetic wave is propagating in the direction and its electric field is given by. The corresponding magnetic field wave is (where B 0 = E 0 /c) A). B). C). D). E). Page 6

7 15. Light traveling in a transparent medium with an index of refraction n 1 is incident on a transparent boundary with a second transparent medium with an index n 2. Very little light is transmitted into the second medium. Which of the following statements must be true? A) n 1 equals n 2 B) n 1 is somewhat greater than n 2 C) n 2 is somewhat greater than n 1 D) n 2 is much greater than n 1 E) Either index of refraction is much greater than the other 16. From directly above (in air: n=1.00), you're watching a fish swim 1.83 m beneath the surface of a clear lake (n = 1.33). How far beneath the surface does the fish seem to be? A) m B) 1.37 m C) 1.83 m D) 2.44 m E) 2.93 m 17. A ray of monochromatic light in air (n=1.00) falls on the upper surface of two parallel-sided slabs of transparent material, as shown in the diagram. The angle of refraction φ in the lower slab is approximately A) 22 B) 30 C) 37 D) 53 E) 60 Page 7

8 18. A negative lens with a focal length of 10.0 cm is on the same axis as a positive lens with a focal length of cm as illustrated. The distance between the lenses is 20.0 cm. A real object 3.0 cm high is placed 20.0 cm to the left of the negative lens. After the light has passed through both lenses, the image is A) 3.0 cm high and virtual. B) 1.0 cm high and virtual. C) 1.0 cm high and real. D) 3.0 cm high and real. E) None of these is correct. 19. An object is placed cm from a screen. When a converging lens is placed between the object and screen at a distance of 160 cm from the object, an image is formed on the screen. Without moving the object or screen, an image can also be formed on the screen when the distance from the object to the lens is A) 8 cm B) 16 cm C) 20 cm D) 32 cm E) 40 cm 20. A stamp collector with a normal near point (25 cm) needs a magnifying power of 10.0 to examine her stamps. If one of the stamps is 2.0 cm wide, what is the angle (in degrees) subtended by the stamp when it is viewed through her magnifier? A) 23 B) 46 C) 0.80 D) 4.6 E) 1.6 Page 8

9 21. To provide large magnification, a telescope should have an objective with a and an eyepiece with a. A) long focal length; short focal length B) long focal length; long focal length C) short focal length; short focal length D) short focal length; long focal length E) large diameter; short focal length 22. Light of wavelength 500 nm illuminates parallel slits and produces an interference pattern on a screen that is 1 m from the slits. In terms of the initial intensity I 0 (of the light passing through either one or the other slit), the light's intensity in the interference pattern at a point for which the path difference is 300 nm is A) I 0 B) I 0 C) I 0 D) I 0 E) I The diffraction pattern of a single slit is shown in the figure. The point at which the path difference of the extreme rays (rays passing through right at the upper and lower edges of the slit) is two wavelengths is A) 1 B) 2 C) 3 D) 4 E) 5 Page 9

10 24. Two slits of width a = mm are separated by a distance d = mm and illuminated by light of wavelength λ = 450 nm. The number of bright fringes seen in the central diffraction pattern maximum is A) 8 B) 16 C) 25 D) 37 E) The size of the smallest things that can be seen with an optical microscope is limited by diffraction. Which of the following could help a microscopist see smaller things? A) A more powerful microscope could be used. B) The microscope could have a lens with a shorter focal length. C) The microscope could have a lens with a longer focal length. D) The diameter of the lens could be smaller. E) Light with a shorter wavelength could be used. Page 10

11 Answer Key - Final_draft_exam 1. C 2. D 3. B 4. C 5. B 6. E 7. B 8. C 9. B 10. B 11. B 12. C 13. E 14. B 15. E 16. B 17. B 18. D 19. E 20. B 21. A 22. B 23. E 24. E 25. E Page 11