Chapters 21 - 29 PHYS 2426 - Brooks

This practice test is similar to the actual test. The class test will consist of about 35 questions designed to be completed in about 2 hours. This practice test does not cover every single concept that may be on the actual class test. An answer key is included, but there are no solutions to the problems. Students need to work out all solutions on their own.

Select the response that best answers the given statement.

1. A metal cylinder of radius 2.0 mm is concentric with another

metal cylinder of radius 5.0 mm. If the space between the cylinders is filled with air and the length of the cylinders is 50 cm, the capacitance of the arrangement is

a. 30 pF b. 60 pF c. 11 pF d. 22 pF 2. To produce higher voltages, the cells of a battery are

connected in series. True or false? a. True b. False 3. If in the diagram I1 = 2A, what is the current through the

2 Ω resistor?

a. 2 A, up b. 2 A, down c. 5 A, up d. 5 A, down

4. If a molecule of oxygen in air has a translational kinetic energy of 1/40 eV, what is its speed?

a. 390 m/s b. 550 m/s c. 2200 m/s d. 15000 m/s 5. The mass of an electron is 9.11 x 10-31 kg. The mass of one

(negative) coulomb of electrons is a. 1 gram b. 5.69 x 10-12 kg c. 5.48 x 10-7 kg d. 2.7 x 1019 /cm3 6. If the net flux through a closed surface is zero, then there

can be no charge or charges within that surface. True or false?

a. True b. False 7. The electron volt is a unit for a. potential b. gradient c. electron potential d. energy 8. A 6-Ω resistor, an 8-Ω resistor, and a 24-Ω resistor are

connected together. What is the minimum resistance that can be produced using all three resistors?

a. 3 Ω b. 4 Ω c. 7 Ω d. (1/24) Ω 9. The fatter a given length of wire is the higher its

resistance will be. True or false? a. True b. False 10. A 1 mF, a 2 mF, and a 3 mF capacitor are connected in series,

the combination being connected across a 9 volt battery. The capacitor with the greatest charge on it is

a. the 1 mF b. the 2 mF c. the 3 mF d. neither since they all have the same charge

11. An ideal ammeter is one that does not change the behavior of

a circuit when it is properly used to measure current. The internal resistance of such a meter is

a. 0 Ω b. the same resistance as the circuit c. infinite d. dependent on the circuit 12. The peak voltage of a 120-V ac line is a. 220 V b. 170 V c. 120 V d. 110 V 13. Parallel plate capacitor #1 has twice the plate area and

twice the plate separation of capacitor #2. The capacitance of the second capacitor is

a. the same as the first b. double the first c. quadruple the first d. eight times the first 14. If in the diagram I1 = 2A, what is V2?

a. 10 V b. 22 V c. 30 V d. 34 V 15. If the voltage between the plates of a parallel plate

capacitor is doubled, the capacitance of the capacitor a. is halved b. remains the same c. is doubled d. quadruples

16. If the potential is given by V = xy - 3z-2, then the electric field has a y-component

a. x b. y c. x + y d. x + y - 6z-3 17. An oxygen ion, O++, is enclosed in a gaussian surface. The

flux leaving that surface is a. 3.2 x 10-19 Nm2/C b. 3.6 x 10-8 Nm2/C c. 8.86 x 10-12 Nm2/C d. 2 Nm2/C 18. A charge Q is uniformly distributed throughout a

nonconducting sphere of radius R. What is the magnitude of the electric field at a distance R/2 from the center of the sphere?

a. Q/2πεoR2

b. Q/4πεoR2

c. Q/8πεoR2

d. Q/16πεoR2 19. What is the resistance between points a and b?

a. 3 Ω b. 8.2 Ω c. 8.25 Ω d. 9 Ω 20. When static equilibrium is established for a charged

conductor, the electric field just inside the surface of the conductor is

a. equal to the field outside b. equal to the perpendicular component of the field outside c. opposite to the field outside d. zero

21. If an electron is accelerated from rest through a potential difference of 25,000 volts in a color television picture tube, its kinetic energy will be

a. 4.0 x 10-15 J b. 4.0 x 10-5 J c. 2.5 x 104 J d. 1.6 V 22. Three equal charges are located at the corners of an

equilateral triangle. If each of the charges were to be doubled, then the resulting force on each of the charges

a. remains the same b. doubles c. triples d. quadruples 23. The voltage between two parallel plates separated by a

distance of 3.0 cm is 120 V. The electric field between the plates is

a. 4000 V/m b. 2000 V/m halfway between the plates c. up to 4000 V/m depending on position d. 3.6 V/m 24. A 1200-W toaster draws more current than a 1000-W toaster.

True or false? a. True b. False 25. If a point charge is located at the center of a cylinder and

the electric flux leaving one end of the cylinder is 20% of the total flux leaving the cylinder, what portion of the flux leaves the curved surface of the cylinder?

a. 20% b. 40% c. 60% d. 80% 26. If a 10 A current flows for two minutes, how much charge has

passed through this circuit? a. 10 C b. 12 C c. 20 C d. 1200 C 27. If the voltage on a capacitor is doubled, then the energy

stored by the capacitor a. stays the same b. doubles c. quadruples d. halves

28. A uniform spherical shell of charge of radius R surrounds a point charge at its center. The point charge has value Q and the shell has total charge -Q. The electric field at a distance R/2 from the center

a. is zero b. does not depend on the charge of the spherical shell c. is half of what it would be if only the point charge were

present d. is directed inward if Q>0. 29. A 1 pF capacitor is connected in parallel with a 2 pF

capacitor, the parallel combination then being connected in series with a 3 pF capacitor. The resulting equivalent capacitance is

a. 1.5 pF b. 3 pF c. 4.5 pF d. 6 pF 30. If the current density in a wire is given by j = kr, 0 < r <

R, where R is the radius of the wire, the current in the wire is

a. kR2 b. kR2/2 c. kR3/3 d. 2ãkR3/3 31. In the circuit shown, the current in the 4-Ω resistor is 1.5

A. What is the current through the 5-Ω resistor?

a. 1 A b. 1.5 A c. 3 A d. 6 A

32. If a point charge is located at the center of a cube and the electric flux through one face of the cube is 5.0 Nm2/C, what is the total flux leaving the cube?

a. 5.0 Nm2/C b. 20 Nm2/C c. 25 Nm2/C d. 30 Nm2/C 33. The earth's northern magnetic pole acts like a. the north pole of a magnet b. the south pole of a magnet c. it has positive charge d. it has negative charge 34. A current I flows in a straight wire of length L at an angle

of 30˚ from the direction of a magnetic field B. The magnitude of the force on this wire is

a. 0 b. BIL c. 0.5 BIL d. not given 35. A current is flowing in a wire in direction 3i + 4j where the

direction of the magnetic field is 5j + 12k. The force on the wire is in the direction

a. 0.71(i + j) b. 0.78i - 0.58j + 0.24k c. 0.78i + 0.58j + 0.24k 36. An alpha particle is moving at a speed of 5 x 105 m/s in a

direction perpendicular to a uniform magnetic field of strength 4 x 10-2 T. The charge on an alpha particle is

3.2 x 10-19 C and its mass is 6.6 x 10-27 kg. As the alpha particle moves, its velocity

a. decreases b. is still perpendicular to the magnetic field c. gains a component in the direction of the magnetic field d. gains a component opposite to the direction of the

magnetic field 37. An alpha particle is moving at a speed of 5 x 105 m/s in a

direction perpendicular to a uniform magnetic field of strength 4 x 10-2 T. The charge on an alpha particle is

3.2 x 10-19 C and its mass is 6.6 x 10-27 kg. The magnitude of the force on the alpha particle is

a. 0 b. 6.4 x 10-15 N c. dependent upon the alpha particle's mass d. answers b and c are correct

38. An alpha particle is moving at a speed of 5 x 105 m/s in a

direction perpendicular to a uniform magnetic field of strength 4 x 10-2 T. The charge on an alpha particle is

3.2 x 10-19 C and its mass is 6.6 x 10-27 kg. The radius of the path of the alpha particle is

a. changing b. 0.26 m c. 0.52 m d. 3.9 m

39. An alpha particle is moving at a speed of 5 x 105 m/s in a

direction perpendicular to a uniform magnetic field of strength 4 x 10-2 T. The charge on an alpha particle is

3.2 x 10-19 C and its mass is 6.6 x 10-27 kg. The time it takes the alpha particle to complete one revolution around its path is

a. 5.2 x 10-7 s b. 1.0 x 10-6 s c. 3.2 x 10-6 s d. 6.5 x 10-6 s

40. A proton is moving at a speed of 3.2 x 106 m/s at an angle of

80° to a uniform magnetic field of strength 1.5 x 10-4 T. What is the direction of the force on the proton?

a. perpendicular to the magnetic field b. parallel to the magnetic field c. at an angle of 80ø to the magnetic field d. at an angle of 10ø to the magnetic field 41. A rectangular loop of wire of width 10 cm and length 20 cm

has a current of 2.5 A flowing through it. Two sides of the loop are oriented parallel to a uniform magnetic field of strength 0.037 T, the other two sides being perpendicular to the magnetic field. The torque on the loop is

a. 0.025 m•N b. 0.050 m•N c. 0.0093 m•N d. 0.019 m•N 42. A wire carries a current directly upwards in the wall of a

house. The direction of the magnetic field due to this current at a point directly east of the wire is directed

a. north b. south c. east d. in a direction that cannot be found with the information

given

43. Two parallel wires carry currents in the same direction. The

current in one wire is doubled, the other current remaining constant. The force between the wires

a. remains the same b. doubles c. quadruples d. rotates 90 degree 44. A superconducting wire has a mass of 0.15 g per meter of

length. If the earth's magnetic field is horizontal and of magnitude 0.5 x 10-4 T, what current would the wire have to carry if the magnetic force on the wire equals the gravitational force.

a. 2.9 A b. 29 A c. 290 A d. 2900 A 45. The coulomb is the same as a. A•s b. A/s c. T•A/m d. all of the above 46. In using Ampere's law, the integral a. must be evaluated around a circular path b. must be evaluated around a closed path c. must be evaluated around a path that lies in a plane d. must be evaluated in a counter-clockwise direction 47. A circular loop of wire of radius 10 cm carries a current of

6A. The magnetic field at the center of the loop is a. 3.8 x 10-7 T b. 1.2 x 10-7 T c. 1.2 x 10-5 T d. 3.8 x 10-5 T 48. A semicircular wire of radius R connects two straight wire

segments. If a current I flows along the wire, the magnetic field at the center of the semicircular wire due to the current in the semicircular wire is

a. εoI/2R

b. εoI/4R

c. εoI/8R

d. εoI/4πR

49. The magnetic field at the center of a square loop of side L

is εoI/4πL times

a. 23/2 b. 27/2 c. 2-1/2 d. 2 50. Magnetic flux depends upon a. the magnetic field b. the area involved c. the orientation of the area with respect to the field d. all of the above 51. A ten loop coil of area 0.23 m2 is in a 0.047 T uniform

magnetic field oriented so that the maximum flux goes through the coil. This flux is

a. 1.1 x 10-3 Tm2 b. 1.1 x 10-2 Tm2 c. 1.1 x 10-1 Tm2 d. 3.4 x 10-2 Tm2 52. A ten loop coil of area 0.23 m2 is in a 0.047 T uniform

magnetic field oriented so that the maximum flux goes through the coil. The emf induced in the coil is

a. 0 b. 1.1 x 10-3 V c. 1.1 x 10-2 V d. 1.1 x 10-1 V 53. A circular loop of wire of area 25 cm2 lies in the plane of

the paper. An increasing magnetic field B is coming out of the paper. What is the direction of the induced current in the loop?

a. There is no current b. clockwise c. counterclockwise d. counterclockwise then clockwise 54. A circular loop of wire of area 25 cm2 lies in the plane of

the paper. An decreasing magnetic field B is coming out of the paper. What is the direction of the induced current in the loop?

a. There is no current b. clockwise c. counterclockwise d. counterclockwise then clockwise

55. A circular loop of wire is in the plane of the paper. The

north pole of a bar magnet is being moved toward the center of the loop from a position in front of the paper. The direction of the induced current in the loop is

a. north b. south c. clockwise d. counterclockwise 56. A 200-loop coil of cross sectional area 8.5 cm2 lies in the

plane of the paper. Directed out of the plane of the paper is a magnetic field of 0.06 T. The field out of the paper decreases to 0.02 T in 12 milliseconds. What is the direction of the current induced?

a. clockwise b. counterclockwise c. clockwise to counterclockwise d. counterclockwise to clockwise 57. If the number of turns on the secondary coil of a transformer

are less than those on the primary, the result is a a. step-down transformer b. step-up transformer c. a 120-V transformer d. a dc transformer 58. A transformer changes the 10,000 V power line to 120 V. If

the primary coil contains 750 turns, how many turns are on the secondary?

a. 3 b. 9 c. 2.1 x 104 d. 6.3 x 104

59. A conducting rod of length L is moving perpendicular to a magnetic field B. As the speed doubles, the magnitude of the motional emf

a. stays the same b. doubles c. quadruples d. halves 60. A conducting rod of length L = 0.65 m and resistance 2.0 ohms

is moved with speed v = 15 m/s perpendicular to a magnetic field B = 4.4 x 10-3 T. The magnitude of the electric field in the rod is

a. 4.3 x 10-2 V/m b. 6.6 x 10-2 V/m c. 6.8 x 10-3 V/m d. 6.1 x 10-5 V/m

ANSWERS 1. a 2. True 3. d 4. a 5. b 6. False 7. d 8. a 9. False 10. d 11. a 12. b 13. a 14. b 15. b 16. a 17. b 18. a 19. b 20. d 21. a 22. d 23. a 24. False 25. c 26. d 27. c 28. b 29. a 30. d 31. b 32. d 33. b 34 c 35. b 36. b 37. b 38. b 39. c 40. a 41. d 42. a 43. b 44. b 45. a 46. b 47. d 48. b 49. b

50. d 51. b 52. a 53. b 54. c 55. d 56. b 57. a 58. b 59. b 60. b

METRIC PREFIXES

εo = 8.85 x 10-12 C2/Nm2

Prefix: Symbol: Magnitude:

Yotta- Y 1024

Zetta- Z 1021

Exa- E 1018

Peta- P 1015

Tera- T 1012

Giga- G 109

Mega- M 106

myria- my 104

kilo- k 103

hecto- h 102

deka- da 10

Prefix: Symbol: Magnitude:

deci- d 10-1

centi- c 10-2

milli- m 10-3

micro- μ 10-6

nano- n 10-9

pico- p 10-12

femto- f 10-15

atto- a 10-18

zepto- z 10-21

yocto- y 10-24