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Physics 1112 Spring 2010 University of Georgia Instructor: HBSchüttler PHYS 1112 In-Class Exam #2B Thu. March 18, 2010, 11:00am-12:15pm This is a closed-book, closed-notes exam, but you are permitted to bring and use a copy of the official Formula Sheet for this exam, which you should have printed out from the PHYS1112 web page. The exam consists of 12 multiple-choice questions. Each question is worth one raw score point. There will be no penalty for wrong answers. No partial credit will be given. I recommend that you read all the questions at the start so that you can allocate your time wisely. (Answer the easy questions first!) You may use a scientific calculator for arithmetic only; your calculator must be non-graphing, non-programmable, and non-algebraic. You are not allowed to share your calculator. The use of cell phones, pagers, PDAs, or any other electronic devices (besides calculators) is forbidden. All such gadgets must be turned off and put away; distractions caused by these devices will not be tolerated. • Do not open the exam until you are told to begin. • Make sure the scantron sheet has your name and your UGA Card ID (810-...) number filled in. Make sure you also have entered your name, UGA Card ID number and signature on the exam cover page (this page!) below. • At the end of the exam period you must hand in both your scantron sheet and this exam cover page, signed and with your name and UGA Card ID (810-...) number filled-in. You may keep all other pages (pages 3+) of this exam paper. • Your exam will not be graded, and you will receive a score of zero, if you do not hand in both a properly filled in scantron sheet and this properly filled-in and signed exam cover page. • You have until the end of the class period (i.e. until 10:45am for Period 2 Class, until 12:15pm for Period 3 Class) to finish the exam and hand in the required exam materials described above. By signing below, you indicate that you understand the instructions for this exam and agree to abide by them. You also certify that you will personally uphold the university standards of academic honesty for this exam, and will not tolerate any violations of these standards by others. Unsigned exams will not be graded. Name (please print): UGACard ID (810-...) #: Signature: 1 Physics 1112 Spring 2010 University of Georgia Instructor: HBSchüttler WORKSPACE 2 Physics 1112 Spring 2010 University of Georgia Instructor: HBSchüttler Conceptual Problems Problem 1: A beam of coherent (laser) light of wavelength λ is incident upon a diffraction grating with line spacing d, with λ < d, as shown in the figure below. Assume |∆y| is the distance (in cm) between the two 1st-order intensity maxima, observed on a screen at a distance L on the other side of the grating. This distance |∆y| will 1st order maxima Fig. 2.03 Δy Screen θ L Diff. Grating Laser Beam (A) (B) (C) (D) (E) decrease if we increase L (keeping λ and d fixed); decrease if we increase λ (keeping L and d fixed); decrease if we increase d (keeping λ and L fixed); increase if we decrease λ (keeping L and d fixed); increase if we increase d (keeping λ and L fixed). Problem 2: If two point charges Q1 and Q2 at some distance r repel each other with a force of 160N, what force would they exert on each other if r is quadrupled (×4); Q1 is tripled with unchanged sign; and the sign of Q2 is reversed ? The two charges will (A) (B) (C) (D) (E) attract each other with a force of 120N attract each other with a force of 2560N attract each other with a force of 30N repel each other with a force of 2560N repel each other with a force of 30N Problem 3: In the figure below, Q1 and Q2 are both negative point charges with |Q1 | and |Q2 | being of comparable magnitude. Which arrow drawn at P could correctly represent the ~ generated by Q at P ? electric field vector E 3 Physics 1112 Spring 2010 University of Georgia Instructor: HBSchüttler Fig. 2.12 P (D) Q2 (E) (C) (A) (B) Q1 (A) (B) (C) (D) (E) Problem 4: In Experiment 1 an electron travels from point A to point B, in the electric ~ generated by/between two oppositely charged capacitor plates, as shown in the figure field E below. In Experiment 2 a proton travels from point A to point B, in the same electric field between the same two charged capacitor plates. A proton has a charge +e and an electron has a charge −e. Fig. 2.14 ------------------------E A B E +++++++++++++++++++++++++++ Assume the electron experiences a rise in electric potential, ∆V = +250V, and a loss of potential energy, ∆U = −40aJ (where 1aJ ≡ 10−18 J), in traveling from A to B. What will the proton experience ? (A) (B) (C) (D) (E) ∆V ∆V ∆V ∆V ∆V = −25V and ∆U = −4aJ = −50V and ∆U = −8aJ = +50V and ∆U = +8aJ = −250V and ∆U = −40aJ = +250V and ∆U = +40aJ Numerical Problems Problem 5: If a double slit is illuminated at normal incidence by coherent (laser) light it produces 5th order maxima at angles ±75o measured from the central (0th order) intensity maxium. At what angles θ, measured from the central (0th order) intensity maxium, will the 3rd order maxima be observed ? 4 Physics 1112 Spring 2010 (A) (B) (C) (D) (E) University of Georgia Instructor: HBSchüttler ±45.0o ±22.5o ±18.8o ±70.8o ±35.4o Problem 6: Two point charges lie on the x-axis: Q1 = −60µC is at x = 0, and Q2 is at x = 15.0cm. A third charge q will be in equilibrium when placed at x = 10.0cm. Therefore, Q2 is (A) (B) (C) (D) (E) −90µC −15µC +30µC +15µC −30µC Problem 7: Two point charges, spaced 112.4m apart, repel each other with a force of 96.0N. What is the amount of the larger point charge if the larger charge is 2.4 times the smaller charge? (A) (B) (C) (D) (E) 7.5mC 13.2mC 18.0mC 22.8mC 27.6mC Problem 8: If a charge of −360nC is uniformly spread out over a single thin, squareshaped sheet of gold foil, of 3.0m sidelength, what is the strength and the direction of the electric field generated by that charge, very close to the surface and far from the edges of that foil? ~ pointing towards the foil (A) 0.1395 × 103 N/C, E ~ pointing towards the foil (B) 2.260 × 103 N/C, E ~ pointing towards the foil (C) 28.76 × 103 N/C, E ~ pointing away from the foil (D) 0.1395 × 103 N/C, E ~ pointing away from the foil (E) 28.76 × 103 N/C, E Problem 9: The total electric flux passing through the approximately spherical surface of a real football (i.e., a soccer ball !!) is Φ = +452Nm2 /C (assuming outward directed normal to the surface). What is the total electric charge enclosed inside the ball ? 5 Physics 1112 Spring 2010 (A) (B) (C) (D) (E) University of Georgia Instructor: HBSchüttler −3.20nC +2.40nC −1.60nC −4.80nC +4.00nC Problem 10: The 900µF capacitor in a defibrillator must be charged to store ±270mC in its two plates. What charging voltage is required for this ? (A) (B) (C) (D) (E) 300V 400V 500V 600V 700V Problem 11: How much electric field energy is stored in the defibrillator capacitor in Problem 10 when it is fully charged ? (A) (B) (C) (D) (E) 22.5J 81.0J 40.5J 62.5J 34.5J Problem 12: If the electric field strength between the capacitor plates in Problem 4 is 57.0V/m, what is the magnitude and the direction of the electron’s acceleration ~a, assuming the electron is subject only to the electric force between the plates ? (A) (B) (C) (D) (E) 1.00 × 1013 m/s2 , ~a 1.00 × 1013 m/s2 , ~a 2.25 × 1013 m/s2 , ~a 2.25 × 1013 m/s2 , ~a 2.25 × 1013 m/s2 , ~a pointing pointing pointing pointing pointing leftward downward rightward leftward downward 6