Exam 3--PHYS 102--Spring 2018

Transcription

1 Class: Date: Exam 3--PHYS 102--Spring 2018 Multiple Choice Identify the choice that best completes the statement or answers the question. 1. Which of these statements about a household circuit is true: I. A GFCI turns off if I in >I out II. Devices in a house all operate at the same voltage. III. As you add more devices to a household circuit, the total current increases. IV. The current to a device in a household circuit will decrease if other devices are removed. a. II & III b. I, II, & III c. III & IV d. all of these are correct e. none these are correct 2. On a circuit breaker, you have a 2400 W heater, a 120 W light bulb, and a 60 W radio. When you add a 480 W blender, the circuit breaker turns off. Assume all the devices operate at 120 V. Which of these is the maximum allowed current for the breaker? a. 25 A b. 20 A c. 15 A d. 10 A 3. Consider this circuit. Which of these equations is correct? a. 3-2I I 1 =0 b. 5-6I 2-6=0 c. -6+2I 1-3=0 d. I 2 +I 3 =I 1 e. 3-2I 1 +6I 3 =0 4. Consider the above circuit. I 2 is 0.17 A to the left. What is the magnitude of I 3? a. 4.5 A b. 4.3 A c. 4.7 A d. 3.2 A e. 2.9 A 1

2 5. What is the current through the 3.0 Ω resistor? 7. Which of these plots shows the charge vs time for a charging capacitor? a. 5.3 A b A c. 4.3 A d. 2.7 A e A 6. Consider a series, charging RC circuit for which R = 2.0 MΩ and C=10.0 µf. The capacitor initially has no charge. You hook up a battery with ε=10.0 V. As the capacitor charges, what is the charge on the capacitor after 5.0 seconds? a. A b. B c. C d. D 8. After three time constants, what percentage of the final voltage, emf, is on an initially uncharged capacitor, C, charged through a resistance R? a. 80 µc b. 120 µc c. 20 µc d. 40 µc e. 0 µc a. 10% b. 87% c. 95% d. 99% 2

3 9. Consider a thin wire bent into the shape of a ring of radius of 10 cm that carries a steady 2.0-A current. The value of the magnetic field at the center of the ring is 12. What creates a magnetic field? a. electrons b. magnetic domains c. moving charges d. ferromagnetic materials 13. A magnetic field CANNOT... a. change the kinetic energy of a moving charge b. exert a force on a moving charge c. change the direction of a charge s motion d. change the momentum of a charge a. 45 µt. b. 25 µt. c. 13 µt. d. 6.3 µt. 14. A positive charge is travelling towards a wire as shown. The charge follows a path as shown. What is the direction of the current in the wire? 10. An electron is moving at 3x10 5 m/s in the positive x direction. A magnetic field of 0.8 T is in the positive z direction. The magnetic force on the electron is: a. left b. right c. into the page d. out of the page e. there is no current a. 1x10-14 N, in the +z direction b. 4x10-14 N, in the +y direction c. 3x10-5 N, in the +x direction d. 2x10 5 N, in the +z direction e. 4x10-14 N, in the -y direction 15. A positive particle travels as shown through the magnetic field. In order for the particle to go through undeflected, an electric field must also be present. What must be the direction of that electric field? 11. How far from a straight wire carrying 0.45 A is the magnetic field strength T? a µm b µm c. 2.3 µm d. 7.2 µm a. up b. down c. right d. left 3

4 16. A proton travels in the -x direction, and the magnetic field points in the +y direction. The direction of the force acting on the proton is a. +z b. -y c. -x d. -z 19. These two mirrors sit at an angle of 90º to one another. A ray of light is incident at 60º on the first mirror. What is the angle of reflection (θ r ), with respect to a perpendicular line to the second mirror, as shown? (Angles might not be drawn to scale.) 17. These are types of light in the electromagnetic spectrum (listed alphabetically). Arrange them in order from lowest energy to highest energy: gamma-ray infrared visible x-ray a. visible, infrared, x-ray, gamma-ray b. infrared, visible, x-ray, gamma-ray c. gamma-ray, infrared, visible, x-ray d. gamma-ray, x-ray, infrared, visible e. infrared, visible, gamma-ray, x-ray 18. Which of the following statements is true? I. Newton believed light was a particle because of refraction II. Huygens believed light was a wave because of reflection III. Einstein showed light was a particle because of interference IV. Young showed light was particle because of the photoelectric effect a. II b. III & IV c. II & III d. I & II e. none of these are true a. 60 b. 30 c. 20 d. 10 e Light travels through 3 media as shown here. Which medium has the highest index of refraction? a. Medium 1 b. Medium 2 c. Medium 3 d. all the same 4

5 21. Light travels from glass to air; the index of refraction for glass is 1.5. If the incident angle is 30 degrees, what is the refracted angle? 24. Consider the above question. What is the critical angle? a. 49 b. 42 c. 19 d. 38 e. the light reflects back into the glass 22. Components of some computers communicate with each other through optical fibers having an index of refraction n=1.50. What time in nanoseconds is required for a signal to travel m through such a fiber? a b c d You stand 2.0 m in front of a flat mirror. Which of these correctly give the image distance and magnification of your image? a. image distance = -2.0 m magnification =+1 b. image distance = +2.0 m magnification =+1 c. image distance = -2.0 m magnification = -1 d. image distance = +2.0 m magnification = An image has a magnification of +2. Which of these statements are correct for this image? a ns b ns c ns d ns e ns 23. An optical fiber uses two transparent materials. The core is in the middle of the fiber; light travels through this medium. The cladding covers the core and protects it. You have two media, flint glass (n=1.66) and crown glass (n=1.52). Which of these will serve as the cladding? I. The image is bigger than the object. II. The image is virtual. III. The image is upright. IV. The image is inverted. a. I, II, and III b. I & III c. II & IV d. II & III e. all of these a. flint glass b. crown glass c. either can be the cladding; just put it on the outside d. neither can be the cladding; the cladding must be opaque 5

6 27. Consider this ray diagram. Which ray is drawn incorrectly? a. a b. b c. c d. all are incorrect e. all are correct 28. A flat mirror produces an image that is a. virtual, upright, and the same size as the object b. virtual, inverted, and the same size as the object c. real, upright, and the same size as the object d. real, upright, and smaller than the object 6

7 ID: A Exam 3--PHYS 102--Spring 2018 Answer Section MULTIPLE CHOICE 1. ANS: B PTS: 1 REF: S18 2. ANS: A PTS: 1 REF: S18 3. ANS: C PTS: 1 REF: S18 4. ANS: C PTS: 1 REF: S18 5. ANS: D PTS: 1 REF: S18 6. ANS: C PTS: 1 REF: S18 7. ANS: B PTS: 1 REF: S18 8. ANS: C PTS: 1 REF: S18-OXT 9. ANS: C PTS: 1 REF: S ANS: B PTS: 1 REF: S ANS: C PTS: 1 REF: S18-OXT 12. ANS: C PTS: 1 REF: S ANS: A PTS: 1 REF: S ANS: B PTS: 1 REF: S ANS: B PTS: 1 REF: S ANS: D PTS: 1 REF: S ANS: B PTS: 1 REF: S ANS: E PTS: 1 REF: S ANS: B PTS: 1 REF: S ANS: B PTS: 1 REF: S ANS: A PTS: 1 REF: S ANS: B PTS: 1 REF: S18-OXT 23. ANS: B PTS: 1 REF: S18, OXT 24. ANS: B PTS: 1 REF: S18-OXT 25. ANS: A PTS: 1 REF: S ANS: A PTS: 1 REF: S ANS: E PTS: 1 REF: S ANS: A PTS: 1 REF: S18 1