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Physics 121 Sample Common Exam 3 NOTE: ANSWERS ARE ON PAGE 6 Signature___________________________ Name (Print): _______________________________ 4 Digit ID:________ Section: ______ Instructions: § § § § 1. A) B) C) D) E) Answer all questions 24 multiple choice questions. You may need to do some calculation. Answer each question on on the Scantron sheet using #2 pencil. You may use backs of the question papers for extra space. You may use one side of an 8.5 x 11 sheet or two sides of a 5x8 card as a formula sheet. A default formula sheet is sometimes also provided. Make sure to bring your own calculator – there are none to borrow or share. Please turn off any cell phones, pagers, communication or entertainment devices, etc. Students are not to communicate with each other once the test has started. If you have questions or need something call your proctor or instructor. In the formula F = qvxB: F must be perpendicular to v but not necessarily to B F must be perpendicular to B but not necessarily to v v must be perpendicular to B but not necessarily to F all three vectors must be mutually perpendicular none of the above 2. The magnetic force on a charged particle is in the direction of its velocity if: A) B) C) D) E) it is moving it is moving it is moving it is moving never in the direction of the field opposite to the direction of the field perpendicular to the field in some other direction 3. A uniform magnetic field is in the positive z direction. A positively charged particle is y moving in the positive x direction through the field. The net force on the particle can be made zero by applying an electric field in which direction? A. B. C. D. E. v Positive x Negative x Positive y Negative y Positive z x B z 4. A magnetic field B = 1 T goes out of the plane of the page. A straight wire carries a current 1 A from right to left. Find the direction of force acting on the wire. A) B) C) D) E) out of the page into the page left, in the plane of the page right, in the plane of the page up, in the plane of the page Page 1 of 6 5. The magnetic field B = 0.5i is acting on proton moving in xy plane with velocity 5 5 y . v =10 i +10 j (in m/s) Find the force acting on the proton. A) B) C) D) E) -15 8 x 10 N, in the positive z-direction -15 8 x 10 N, in the negative z-direction -19 1.6 x 10 N, in the positive y-direction -19 1.6 x 10 N, in the negative y-direction zero v o 45 x B z 6. Find the magnitude and direction of the force on a wire 3 mm long which carries a 2mA current. It is vertically oriented with the current flowing toward the bottom. The wire is placed inside a uniform magnetic field of 4 kT that is pointing horizontally to the left. A. 24 N., left B. 24 mN, right B C. 24 kN, top i D. 24 N, bottom E. 24 mN, into the page 7. A proton (mass = 1.67 x 10 -27 kg) is circulating in the plane of the page due to a magnetic field perpendicular to the page and directed into it. The radius of its circulating motion is 9 cm and its speed is 1.6 km/s. Find the value of magnetic field and the direction of the motion. B A. 0.19 µT, counterclockwise F B. 0.19 µT, counterclockwise C. 0.19 mT, clockwise D. 0.19 mT, counterclockwise E. 0.19 T, clockwise The following two problems apply to the description below A positive particle (a proton) with charge 1.6.10-19 C and mass 1.67x10-27 kg is moving with a velocity v= 2.1x105 m/s in the positive z direction. A magnetic field B = 125 x 10-3 T is pointing in the positive y direction . 8. Find the force acting on the particle. A) B) C) D) E) -15 4 x 10 N, in the positive x-direction -15 4 x 10 N, in the negative x-direction -19 1.6 x 10 N, in the positive z-direction -19 1.6 x 10 N, in the negative z-direction zero 9. Find the frequency of proton’s circular motion. A) 1.9 MHz B) C) D) E) 1.2 MHz 0.5 MHz 0.2 MHz 0.1 MHz Page 2 of 6 10. A particle with positive charge q = 0.3x10-6 C is a distance d = 1.5x10-2 m from a long straight wire that carries a current I = 5 A. The particle is traveling with speed v = 1000 m/s perpendicular to the wire. What are the direction and magnitude of the force on the particle if it is moving away from the wire? (in N) A) B) C) D) E) 1.0.10-8 1.0.10-8 2.0.10-8 2.0.10-8 2.0.10-7 up down up down up 11. Two long parallel straight wires carry equal currents in the same direction. At a point midway between the wires, the magnetic field they produce is: A) B) C) D) E) zero non-zero and along a line connecting the wires non-zero and parallel to the wires non-zero and perpendicular to the plane of the two wires none of the above 12. Point P is the center of the semicircle in the accompanying sketch, with current I flowing from left to right as shown. The magnitude and direction of the magnetic field at P are: A)? µ0i/4R, out of paper µ0i/4πR, into paper C) µ0i/4πR, out of paper D) µ0i/4R, into paper E)? µ0i/2R, into paper B) R i P 13. The diagrams show three circuits consisting of concentric circular arcs (either half or quarter circles of radii r, 2r, and 3r) and radial lengths. The circuits carry the same current. Rank them according to the magnitudes of the magnetic fields they produce at C, least to greatest. A) B) C) D) E) 1, 1, 2, 3, 2, 2, 3, 3, 2, 1, 3 2 1 1 3 14. A wire carries a current from the left to the right. What is the direction of the magnetic field above and below the wire? A. Above B. Above C. Above D. Above E. Above – – – – – into the page, Below – out of the page out of the page, Below – into the page left, Below – right right, Below – left bottom, Below – top Page 3 of 6 15. Two straight, parallel wires that are each 5 m long carry currents of 3 A and 5 A in opposite directions. If the perpendicular distance d between the wires is 1 cm, what is the force between them? A. 1.5 mN, repulsion B. 1.5 mN, attraction C. 3.0 mN, repulsion D. 3.0 mN, attraction E. 3.0 N, repulsion d i1 i2 16. Two circular coils of equal radius 2 cm are placed several centimeters apart. If viewed from left, the current in the both loops is clockwise. The direction of magnetic field along the axis passing through the loops' centers and halfway between them A) B) C) D) E) is to the left. is to the right. is oscillating. Is zero depends on the distance between coils The figure at the right applies to the following three problems. A long straight wire is in the plane of the rectangular conducting loop. 17. If the current in the long wire is increased, the induced current in the loop is A) B) C) D) E) clockwise counterclockwise zero downward on both left and right sides of the loop upward on both left and right sides of the loop i 18. If the current in the straight wire remains constant but the loop is moved to the right, the induced current in the loop is A) clockwise B) counterclockwise C) zero D) downward on both left and right sides of the loop E) upward on both left and right sides 19. If the current in the straight wire remains constant but the loop is moved down, the induced current in the loop is A) B) C) D) E) clockwise counterclockwise zero downward on both left and right sides of the loop upward on both left and right sides of the loop 20. A square loop of wire lies in the plane of the page. The magnetic field is directed into the page and its magnitude is decreasing. The induced current in the loop is: A) counterclockwise B) clockwise C) zero D) depends upon whether or not B is decreasing at a constant rate E) clockwise in two of the loop sides and counterclockwise in the other two Page 4 of 6 21. Find the magnitude of the magnetic field inside an ideal solenoid. The current is 1 A and the solenoid has 2500 turns per meter. A) 3.14 GT B) 3.14 µT C) 3.14 mT D) 3.14 T E) 3.14 kT 22. A wire slides to the right with a speed of 10 m/s on two metallic wires 50 cm apart that are connected by a 5.0 Ohm resistor. The slider moves in a region where the magnetic field is 1 T into the page. The magnitude and direction of the current through the resistor are A) B) C) D) E) 5Ω 10 A, up 10 A, down 1 A, up 1 A, down zero 23. A circular UHF television antenna has a diameter of 11 cm. The magnetic field of a TV signal is perpendicular to the plane of the loop and, at one instant of time, its magnitude is changing at the rate 0.16 T/s. The magnetic field is uniform. What emf is induced in the antenna? A) B) C) D) E) 3.0 millivolts 1.5 millivolts 0.75 millivolts 30 millivolts Insufficient information 24. An electric generator consists of N = 500 turns of wire formed into a rectangular loop a = 0.05 m by b = 0.03 m placed entirely in a uniform magnetic field with magnitude B = 2.5 T.. What is the maximum value of the emf produced when the loop is spun at ω = 1000 rev/min about an axis perpendicular to B? A) 196.0 B) 124.1 C) 55.3 D) 39.2 E) 20.3 Page 5 of 6 Answers to Physics 121 Sample Common Exam 3 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. E E C E B E D B A C A D D B A B B A C B C D B A Page 6 of 6