Exam 1--PHYS 102--S14

Transcription

1 Class: Date: Exam 1--PHYS 102--S14 Multiple Choice Identify the choice that best completes the statement or answers the question. 1. The magnitude of the charge on an electron is approximately: a C b C c C d C e C 2. When you charge an object by induction, you... a. touch the ball with a charged object. b. move electrons from your finger to the ball. c. induct the ball with charge. d. bring a charged object near but do not touch the ball. 3. An electrical insulator is a material: a. must be a crystal b. that has more electrons than protons on its surface c. cannot be a pure chemical element d. through which electrons do not flow easily e. containing no electrons 4. The diagram shows two pairs of heavily charged plastic cubes. Cubes 1 and 2 attract each other and cubes 1 and 3 repel each other. Which of the following illustrates the forces of cube 2 on cube 3 and cube 3 on cube 2? a. A d. D b. B e. E c. C 5. In which of the following diagrams is the potential along the x-axis equal to zero? a. a d. none of these b. b e. all of these c. c 1

2 6. Two uncharged metal spheres, L and M, are in contact. A positively charged rod is brought close to L, but not touching it, as shown. The two spheres are slightly separated and the rod is then withdrawn. As a result: 9. Two identical charges, 2.0m apart, exert forces of magnitude 4.0 N on each other. The value of either charge is: a. both spheres are neutral b. both spheres are positive c. both spheres are negative d. L is negative and M is positive e. L is positive and M is negative 7. Two small charged objects attract each other with a force F when separated by a distance d. If the charge on each object is reduced to one-fourth of its original value and the distance between them is reduced to d/2 the force becomes: a. 3.8x10 5 C b. 1.8x10-9 C c. 4.2x10-5 C d. 1.9x10 5 C e. 2.1x10-5 C 10. Consider this arrangement of charges, which are at the vertices of an equilateral triangle (ie. they are all equidistant from one another). Which of the arrows best represents the direction of the net force on the +4q charge? a. F/16 b. F/8 c. F/4 d. F/2 e. F 8. Two particles, X and Y, are 4m apart. X has a charge of 2Q and Y has a charge of Q. The force of X on Y: a. has four times the magnitude of the force of Y on X b. has twice the magnitude of the force of Y on X c. has the same magnitude as the force of Y on X d. has one-fourth the magnitude of the force of Y on X e. has half the magnitude of the force of Y on X a. a b. b c. c d. d 2

3 11. Consider this arrangement of particles. What is the direction of the net force on the +3 µc charge? 14. Two charged particles are arranged as shown. In which region is the electric field 0 N/C? a. III only b. I & III only c. I & II only d. I only e. II only 15. A -1 nc charge floats in an electric field. The only forces on the charge are from gravity and the electric field. The mass of the charge is 1x10-9 kg. What is the magnitude and direction of the electric field? (Let g=10m/s 2 ) a. 45 below the +x axis b. 45 above the +x axis c. along the +x axis d. 135 from the +x axis 12. What is the electric field at a distance of 3 m from a 1 nc charge? a. 1 N/C b. 3 N/C c. 9 N/C d. 9x10 9 N/C 13. A proton is 3 m from a 1nC charge. What initial acceleration does it experience? a. 10 N/C, upwards b. 1 N/C, downwards c. 10 N/C, downwards d. 20 N/C, upwards 16. Consider the charges in this figure. Which of these statements is true? a. 300,000,000 m/s 2 b. 100,000,000 m/s 2 c. 100,000 m/s 2 d. 200,000 m/s 2 a. both charges are positive and have the same magnitude of charge b. both charges are negative; the magnitude of A is larger than that of B c. charge A is positive; charge B is negative; both have the same magnitude charge d. both charges are positive; the magnitude of B is larger than that of A 3

4 17. A proton is accelerated by a constant electric field of magnitude 300 N/C; the proton is moving in the same direction as the electric field and is initially at rest. What distance has the proton moved after 1x10-6 s? 20. Two charges are arranged as shown. What is the potential at point A? a m b. 1.4x10-6 m c. 2.4x10-29 m d. 100 m 18. Where on this line is the potential equal to zero? a. 9 V b. 0 V c. 45 V d. 27 V 21. A charged particle sits in an electric field as shown here. If the particle follows the path shown by the dashed line (ie, upwards), how much work is done to move the particle? a. a b. b c. c d. d e. e 19. Which of these is a conservative force? I. Electric force II. Frictional force III. Gravitational force IV. Electric potential a. II b. I, III, & IV c. I & III d. all of these a. zero work b. positive work c. negative work d. unable to tell without knowing the charge of the particle 4

5 22. What is the potential and electric field at the point P, which is in the center of this square? 26. A 2 C charge crosses 2 plates separated by 0.01 m; the high potential plate is 5V, and the low potential side is -5V. How much kinetic energy does the charge have moving across these 2 plates? (Hint: What is the potential difference between the 2 plates?) a. E 0, V 0 b. E 0, V=0 c. E=0, V=0 d. E=0, V Consider this charge. The arrows represent field lines. The dashed lines represent equipotential lines. What is the sign of the charge? a. 20 J b. 500 J c. 200 J d J e. 5 J 27. An electron is released at position x=a in the potential described by the function in this figure. What direction does it travel? a. positive b. negative c. there is no charge 24. For the previous question, where is the electric potential the least? a. both C & B b. B c. A d. C e. both A & D 25. The unit of electrical potential, the volt, is dimensionally equivalent to: a. J C. b. J/C. c. F C. d. C/J. a. to the left b. to the right c. it remains stationary d. it oscillates around A 28. What amount of work is required to assemble this collection of charges? a. 12 J b. 6.8x10-9 J c. 2.4x10-8 J d. 1.3x10-8 J 5

6 ID: A Exam 1--PHYS 102--S14 Answer Section MULTIPLE CHOICE 1. ANS: B PTS: 1 2. ANS: D PTS: 1 3. ANS: D PTS: 1 4. ANS: C PTS: 1 5. ANS: D PTS: 1 6. ANS: D PTS: 1 7. ANS: C PTS: 1 8. ANS: C PTS: 1 9. ANS: C PTS: ANS: C PTS: ANS: A PTS: ANS: A PTS: ANS: B PTS: ANS: D PTS: ANS: C PTS: ANS: A PTS: ANS: A PTS: ANS: B PTS: ANS: C PTS: ANS: A PTS: ANS: A PTS: ANS: B PTS: ANS: A PTS: ANS: E PTS: ANS: B PTS: ANS: A PTS: ANS: A PTS: ANS: C PTS: 1 1