P202 Practice Exam 2 Spring 2004 Instructor: Prof. Sinova

Transcription

1 P202 Practice Exam 2 Spring 2004 Instructor: Prof. Sinova Name: Date: (5)1. How many electrons flow through a battery that delivers a current of 3.0 A for 12 s? A) 4 B) 36 C) D) E) (5)2. The potential difference across the ends of a wire is doubled in magnitude. If Ohm's law is obeyed, which one of the following statements concerning the resistance of the wire is true? A) The resistance is one half of its original value. B) The resistance is twice its original value. C) The resistance is not changed. D) The resistance increases by a factor of four. E) The resistance decreases by a factor of four. (10)3. A 40-W and a 60-W light bulb are designed for use with the same voltage. What is the ratio of the resistance of the 60-W bulb to the resistance of the 40-W bulb? A) 1.5 B) 0.67 C) 2.3 D) 0.44 E) 3.0 (5)4. Which one of the following statements concerning resistors in series is true? A) The voltage across each resistor is the same. B) The current through each resistor is the same. C) The power dissipated by each resistor is the same. D) The rate at which charge flows through each resistor depends on its resistance. E) The total current through the resistors is the sum of the current through each resistor. Page 1

2 (15)5. Three resistors and two batteries are connected as shown in the circuit diagram. What is the magnitude of the current through the 18 ohms resistor? A) 0.15 A B) 0.82 A C) 0.30 A D) 0.67 A E) 0.52 A (5)6. Three parallel plate capacitors, each having a capacitance of 1.0 µf are connected in parallel. What is their equivalence capacitance? A) 3 µf B) 3 F C) 0.33 µf D) 3.3 µf E) 30 µf (5)7. An electron is moving with a speed of m/s when it encounters a magnetic field of 0.60 T. The direction of the magnetic field makes an angle of 60.0 with respect to the velocity of the electron. What is the magnitude of the magnetic force on the electron? A) N B) N C) N D) N E) N Page 2

3 (5)8. An electron traveling horizontally enters a region where a uniform magnetic field is directed into the plane of the paper as shown. Which one of the following phrases most accurately describes the motion of the electron once it has entered the field? A) upward and parabolic B) upward and circular C) downward and circular D) upward, along a straight line E) downward and parabolic (10)9. A loop of wire with a weight of 1.47 N is oriented vertically and carries a current I = 1.75 A. A segment of the wire passes through a magnetic field directed into the plane of the page as shown. The net force on the wire is measured using a balance and found to be zero. What is the magnitude of the magnetic field? A) zero tesla B) 0.51 T C) 0.84 T D) 1.5 T E) 4.2 T Page 3

4 Two long, straight, parallel wires separated by a distance d carry currents in opposite directions as shown in the figure. The bottom wire carries a current of 6.0 A. Point O is a distance 0.50d below the 6-A wire. The total magnetic field at point O is zero tesla. (15)10. Determine the value of the current, I, in the top wire. A) 2 A B) 3 A C) 6 A D) 18 A E) This cannot be determined since the value of d is not specified (5)11. A conducting loop of wire is placed in a magnetic field that is normal to the plane of the loop. Which one of the following actions will not result in an induced current in the loop? A) Rotate the loop about an axis that is parallel to the field and passes through the center of the loop. B) Increase the strength of the magnetic field. C) Decrease the area of the loop. D) Decrease the strength of the magnetic field. E) Rotate the loop about an axis that is perpendicular to the field and passes through the center of the loop. Page 4

5 (5)12. A metal ring is dropped from rest below a bar magnet that is fixed in position as suggested in the figure. An observer views the ring from below. Which one of the following statements concerning this situation is true? A) As the ring falls, an induced current will flow counterclockwise as viewed by the observer. B) As the ring falls, an induced current will flow clockwise as viewed by the observer. C) As the ring falls, there will be an induced magnetic field around the ring that appears counterclockwise as viewed by the observer. D) As the ring falls, there will be an induced magnetic field around the ring that appears clockwise as viewed by the observer. E) Since the magnet is stationary, there will be no induced current in the ring. Page 5

6 Two coils, 1 and 2, with iron cores are positioned as shown in the figure. Coil 1 is part of a circuit with a battery and a switch. (5)13. Immediately after the switch S is closed, which one of the following statements is true? A) An induced current will flow from right to left in R. B) An induced current will flow from left to right in r. C) A magnetic field that points toward B appears inside coil 1. D) An induced magnetic field that points toward B appears inside coil 2. E) A current will pass through r, but there will be no current through R. (5)14. Assume the switch S has been closed for a long time. Which one of the following statements is true? A) An induced current will flow from right to left in R. B) An induced current will flow from left to right in r. C) A magnetic field that points toward B appears inside coil 1. D) An induced magnetic field that points toward B appears inside coil 2. E) A current will pass through r, but there will be no current through R. Page 6

7 Answer Key (THIS IS THE CORRECT ANSWER KEY, THE ONE THAT WAS POSTED OVER THE WEEKEND DID NOT CORRESPOND TO THE TEST) 1. E 2. C 3. B 4. B 5. D 6. A 7. E 8. C 9. E 10. D 11. A 12. B 13. A 14. E Page 7