Unformatted text preview: PHYSICS 222 Fall 2010 EXAM 2: November 4, 2010 8:00pm--10:00pm Name (printed): ______________________________________________________________________ Recitation Instructor: ________________________________________________ Section #_______ INSTRUCTIONS: This exam contains 25 multiplechoice questions, plus two extracredit questions, each worth 3 points. Choose one answer only for each question. Choose the best answer to each question. Answer all questions. Allowed material: Before turning over this page, put away all materials except for pencils, erasers, rulers and your calculator. There is a formula sheet attached at the end of the exam. Other copies of the formula sheet are not allowed. Calculator: In general, any calculator, including calculators that perform graphing, is permitted. Electronic devices that can store large amounts of text, data or equations (like laptops, palmtops, pocket computers, PDA or ebook readers) are NOT permitted. If you are unsure whether or not your calculator is allowed for the exam, ask your TA. How to fill in the bubble sheet: Use a number 2 pencil. Do NOT use ink. If you did not bring a pencil, ask for one. In case you are using a new bubble sheet: Write and fill in the bubbles corresponding to: Please turn over your bubble sheet when you are not writing on it. If you need to change any entry, you must completely erase your previous entry. Also, circle your answers on this exam. Before handing in your exam, be sure that your answers on your bubble sheet are what you intend them to be. You may also copy down your answers on a piece of paper to take with you and compare with the posted answers. You may use the table at the end of the exam for this. When you are finished with the exam, place all exam materials, including the bubble sheet, and the exam itself, into your folder and return the folder to your recitation instructor. No cell phone calls allowed. Either turn off your cell phone or leave it at home. Anyone answering (or using) a cell phone must hand in their work immediately; their exam is over. Best of luck, Paul Canfield and Paula Herrera Your last name, middle initial, and first name. Your ID number (the middle 9 digits on your ISU card) Special codes K to L are your recitation section. (Honors sections: H1 10 ; H2 23). Always use two digits (e.g. 01, 09, 11, 13) Note that questions are numbered 28 through 54. 28. What is the potential difference across the capacitor in the circuit below a long time after the switch has been closed? A. B. C. D. E. 100 10 V 15 V 20 nF 25 V 35 V 50 V 50 V 29. Which of the following equations is correct, for the currents indicated in the figure? R1 R2 I1 I2 1 2 3 100 A. I1 I2 I3 B. 1 2 I1R1 I2R2 0 C. 1 3 I1R1 I3R3 0 D. 1 2 I1R1 0 E. 2 3 I2R2 I3R3 0 I3 R3 30. Positive particles travel through an infinitely long semiconducting slab with a rectangular cross section. The long side of the slab is aligned with the x axis. There is a uniform magnetic field which points in the y direction. y 1 + v 2 4 3 x B z Consider points 1 through 4 on the sides of the slab as shown in the figure. Which of the following is correct? A. V1 > V3 B. V1 < V4 C. V2 > V4 D. V2 < V4 E. None of the above. 31. In the figure below, the loop is moved toward the solenoid. The figure shows the B field generated by the current flowing through the solenoid. I The current induced in the loop points _____________ and the magnetic field associated with this induced current at the center of the loop points ______________. A. downward along the front of the loop, to the left B. downward along the front of the loop, to the right C. upward along the front of the loop, to the left D. upward along the front of the loop, to the right E. No current or magnetic field is induced in this loop. The situation below pertains to the two following questions At t = 0, a rectangular loop of resistance 10.0 and dimensions L = 8.00 cm and w = 4.00 cm enters a region of constant magnetic field B = 2.00 T directed into the screen as shown. The length of the region containing the magnetic field is LB = 16 cm. The coil is observed to move at a constant velocity v = 1.00 cm/s. 32. What is the current in the loop at t = 1.00 s? A. 4.0 105 A B. 8.0 105 A C. 16 105 A D. 32 105 A E. 64 105 A 33. Which of the following graphs best describes the qualitative behavior of the current as a function of time in the loop, assuming that we take the counterclockwise direction as positive? I I B w L LB v t t A I I B t t C D I t E The situation below pertains to the two following questions A 10.0 mH inductor is connected to a variable capacitor to form an LC circuit. 34. Find the capacitance so that the system oscillates with a frequency of 3000 Hz. A. 1.4 107 F B. 2.8 107 F C. 1.1 105 F D. 2.2 105 F E. 3.2 103 F 35. When the charge in the capacitor is at its peak value, the current in the inductor is ___________ and the potential difference between the plates of the capacitor is _____________ the voltage across the inductor. A. zero, equal to B. zero, larger than C. at its peak value, equal to D. at its peak value, larger than E. None of the above. 36. A triangular current loop has two 30 angles and two identical sides of 6.0 cm each. The loop lies in the xy plane, with the long side parallel to the y axis. A current of 0.50 A circulates in the loop in the direction shown in the figure. A uniform magnetic field B = 0.35 T points in the +x direction. Find the force on side RS of the loop. y A. 5.3 103 N , direction into the page. B. 5.3 103 N , direction out of the page. C. 9.1 103 N , direction into the page. I B D. 9.1 103 N , direction out of the page. S 3 E. 11 10 N , direction out of the page. 30 R x 37. An infinite array of wires parallel to the z axis is used to a make an infinite sheet parallel to the yz plane. There are 400 wires per meter. A current of 4.0 A flows through each wire in the positive z direction. Find the magnetic field at a point on the x axis with x = 3.0 m. y A. 1.0 mT B. 2.0 mT C. 3.0 mT D. 4.0 mT E. 5.0 mT x 38. A current of 5.0 mA flows through a ring of radius R = 2.0 cm. Evaluate the integral B dl on an imaginary circle, also of radius R = 2.0 cm, perpendicular to the plane of the ring, that goes through the center of the ring. A. 0 B. 3.1 109 Tm R C. 6.3 109 Tm R D. 3.1 104 Tm 4 I E. 6.3 10 Tm 39. The circuit below consists of three identical bulbs and an ideal battery. The switch is initially open. When the switch is closed, bulb 1 glows _____________ and bulb 2 glows ____________ (as compared to before the switch was closed). A. dimmer, dimmer B. brighter, dimmer C. dimmer, brighter D. the same, the same, E. the same, brighter 40. A real battery (with an emf = 12.0 V and an internal resistance of 2.00 ) is part of a single loop circuit with two 10.0 resistors that are wired in parallel and are then in series with a 5.00 resistor. If an ideal voltmeter is placed across the battery's terminals, what voltage does it read? A. 5.00 V B. 7.00 V C. 9.00 V D. 10.0 V E. 12.0 V 41. An ideal battery, = 10.0 V, a 100 resistor, a capacitor and a switch are wired into a single loop circuit. The capacitor is initially uncharged. After the switch is closed, it takes the battery 1.00 s to charge to 5.00 V. What is the value of the capacitor? A. 7.20 mF B. 10.0 mF C. 14.4 mF D. 20.0 mF E. 21.6 mF 42. In the sketch to the right, a long, straight wire carries a current of 30.0 A and the rectangular loop carries a current of 15.0 A, as shown. Consider the situation where the dimension w of the loop is taken to: (i) the small w limit (w 0) (ii) the large w limit (w ) Which of the following statements is correct? A. B. C. D. E. 43. Two vertical, straight wires carry 3.00 A currents and are separated by 1.00 cm, as shown in the sketch to the right. Which of the following is correct? A. Each wire experiences a force of 18 105 N/m to the left. B. Each wire experiences a force of 18 105 N/m to the right. C. Each wire experiences a force of 18 107 N/m to the left. D. Each wire experiences a force of 18 107 N/m to the right. E. None of the above. For the small w limit, the force on the loop approaches zero. For the large w limit, the force on the loop approaches zero. For both the large and small w limits, the force on the loop approaches zero. For the small w limit, the force approaches a finite, constant value. None of the above are correct. 44. A stiff wire bent into a semicircle of radius a is rotated with frequency f in a uniform magnetic field, as shown in the figure below. If a = 10 cm and B = 0.1 T, how large does f have to be to achieve a 100 V amplitude? A. 5.07 103 Hz B. 1.01 104 Hz C. 1.52 104 Hz D. 3.18 104 Hz E. 6.37 104 Hz 45. The electron beam in an oscilloscope is coming out of the page of the paper before it hits the screen. As the two magnets shown in the figure are brought closer to opposing sides of an oscilloscope tube, in what direction will the spot created by the beam on the screen move? A. B. C. D. E. Up Down Right Left Will not move S Oscilloscope screen N Beam of electrons (out of the page) 46. A proton and an electron are shot horizontally into a region of uniform, vertical magnetic field with the same speeds. Which of the following is correct? A. They each will deflect in the same direction with the same radii of curvature. B. They will deflect in opposite directions with the same radii of curvature. C. They each will deflect in the same direction and the electron will have a larger radius of curvature than the proton. D. They will deflect in opposite directions and the electron will have a larger radius of curvature than the proton. E. They will deflect in opposite directions and the electron will have a smaller radius of curvature than the proton. 47. A rod of copper has a radius of 1.00 cm and is 20.0 cm long. It is held vertically (along the z direction) and moved in the positive x direction in a uniform, horizontal magnetic field of 2.00 T that points along the positive y direction. If it moves with a speed of 100 km/h, what is the magnitude of the potential difference that exists between the two ends of the rod? A. 11.1 V B. 40.0 V C. 55.6 V D. 111 V E. 5560 V 48. A 1.00 m long rod is placed on a scale and weighs 10.0 N when there is no current flowing through it. Let gravity define the negative z direction of this right handed coordinate system. It is aligned so that current flows through it along the positive y direction and there is a 1.00 T magnetic field pointing along the positive x direction. What does the scale read when a 5.00 A current flows? A. 0 N B. 5.00 N C. 10.0 N B g D. 15.0 N E. 20.0 N I 49. An inductor is made by winding 1000 loops of wire around a 1.00 cm2 cross section tube that is 2.00 cm long. What size resistor needs to be used with this inductor so as to give a LRtime constant of 1.00 ms? A. B. C. D. E. 2.51 103 2.51 101 2.51 104 6.28 100 6.28 104 50. How much current must flow through a 1 mH, ideal inductor so that it stores the same energy as a 1 mF, ideal capacitor that has a 10 V potential between the plates? The inductor is made out of copper wire and the capacitor is made using a dielectric material with = 10. A. B. C. D. E. 51. A thick copper cable with a 1.00 cm radius carries a 1000 A current uniformly distributed throughout its cross section. Let: B(1.00 cm) = magnetic field measured just outside of the wire (1.00 cm from its center). B(0.50 cm) = magnetic field measured at a point inside of the wire, 0.50 cm from the center of the wire. What is the ratio B(0.50 cm)/B(1.00 cm)? A. 0.00 B. 0.25 C. 0.50 D. 1.00 E. 2.00 0.001A 0.01 A 0.1 A 1 A 10 A 52. What is the equivalent resistance of the following configuration of resistors? All resistors have a resistance R. 4 A. R 3 15 B. R 4 8 C. R 3 11 D. R 15 11 E. R 3 53. Take a single loop circuit that consists of a real battery with = 8.00 V and an internal resistance of 10.0 and two resistors, R1 = 7.00 and R2. For what value of R2 will the most power be dissipated in R2? A. B. C. D. E. 7.00 8.00 10.0 17.0 20.0 54. Two infinitely long wires form the x and y axes of a righthanded coordinate system. A current of 5.00 A flows in the positive x direction. A current of 7.00 A flows in the positive y direction. What is the magnetic field at a point P, located at (3.00 m, 1.00 m)? y A. 5.33 107 T out of page B. 5.33 107 T into page 7.00 A C. 14.66 107 T out of page D. 14.66 107 T into page P (3.00, 1.00) m E. 0.00 T 5.00 A x ...
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