test 3 test bank physics 2

Chapter 28: MAGNETIC FIELDS

1. Units of a magnetic eld might be:

A. Cm/sB. Cs/mC. C/kgD. kg/CsE. N/Cm

ans: D

2. In the formula nF = qnv nB:A. nF must be perpendicular to nv but not necessarily to nBB. nF must be perpendicular to nB but not necessarily to nvC. nv must be perpendicular to nB but not necessarily to nFD. all three vectors must be mutually perpendicularE. nF must be perpendicular to both nv and nB

ans: E

3. An electron moves in the negative x direction, through a uniform magnetic eld in the negativey direction. The magnetic force on the electron is:

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y

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z

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A. in the negative x directionB. in the positive y directionC. in the negative y directionD. in the positive z directionE. in the negative z direction

ans: E

4. At any point the magnetic eld lines are in the direction of:

A. the magnetic force on a moving positive chargeB. the magnetic force on a moving negative chargeC. the velocity of a moving positive chargeD. the velocity of a moving negative chargeE. none of the above

ans: E

Chapter 28: MAGNETIC FIELDS 405

5. The magnetic force on a charged particle is in the direction of its velocity if:

A. it is moving in the direction of the eldB. it is moving opposite to the direction of the eldC. it is moving perpendicular to the eldD. it is moving in some other directionE. never

ans: E

6. A magnetic eld exerts a force on a charged particle:

A. alwaysB. neverC. if the particle is moving across the eld linesD. if the particle is moving along the eld linesE. if the particle is at rest

ans: C

7. The direction of the magnetic eld in a certain region of space is determined by ring a testcharge into the region with its velocity in various directions in di&erent trials. The eld directionis:

A. one of the directions of the velocity when the magnetic force is zeroB. the direction of the velocity when the magnetic force is a maximumC. the direction of the magnetic forceD. perpendicular to the velocity when the magnetic force is zeroE. none of the above

ans: A

8. An electron is moving north in a region where the magnetic eld is south. The magnetic forceexerted on the electron is:

A. zeroB. upC. downD. eastE. west

ans: A

9. A magnetic eld CANNOT:

A. exert a force on a charged particleB. change the velocity of a charged particleC. change the momentum of a charged particleD. change the kinetic energy of a charged particleE. change the trajectory of a charged particle

ans: D

406 Chapter 28: MAGNETIC FIELDS

10. A proton (charge e), traveling perpendicular to a magnetic eld, experiences the same force asan alpha particle (charge 2e) which is also traveling perpendicular to the same eld. The ratioof their speeds, vproton/valpha, is:

A. 0.5B. 1C. 2D. 4E. 8

ans: C

11. A hydrogen atom that has lost its electron is moving east in a region where the magnetic eldis directed from south to north. It will be deected:

A. upB. downC. northD. southE. not at all

ans: A

12. A beam of electrons is sent horizontally down the axis of a tube to strike a uorescent screenat the end of the tube. On the way, the electrons encounter a magnetic eld directed verticallydownward. The spot on the screen will therefore be deected:

A. upwardB. downwardC. to the right as seen from the electron sourceD. to the left as seen from the electron sourceE. not at all

ans: C

13. An electron (charge = 1.6 1019 C) is moving at 3 105m/s in the positive x direction. Amagnetic eld of 0.8T is in the positive z direction. The magnetic force on the electron is:

A. 0B. 4 1014N, in the positive z directionC. 4 1014N, in the negative z directionD. 4 1014N, in the positive y directionE. 4 1014N, in the negative y direction

ans: D

14. At one instant an electron (charge = 1.61019 C) is moving in the xy plane, the componentsof its velocity being vx = 5 105m/s and vy = 3 105m/s. A magnetic eld of 0.8T is in thepositive x direction. At that instant the magnitude of the magnetic force on the electron is:

A. 0B. 2.6 1014 NC. 3.8 1014 ND. 6.4 1014 NE. 1.0 1013 N

ans: C


15. At one instant an electron (charge = 1.61019 C) is moving in the xy plane, the componentsof its velocity being vx = 5 105m/s and vy = 3 105m/s. A magnetic eld of 0.8T is in thepositive x direction. At that instant the magnitude of the magnetic force on the electron is:

A. 0B. 3.8 1014 NC. 5.1 1014 ND. 6.4 1014 NE. 7.5 1014 N

ans: B

16. An electron travels due north through a vacuum in a region of uniform magnetic eld nB thatis also directed due north. It will:

A. be una&ected by the eldB. speed upC. slow downD. follow a right-handed corkscrew pathE. follow a left-handed corkscrew path

ans: A

17. At one instant an electron is moving in the positive x direction along the x axis in a regionwhere there is a uniform magnetic eld in the positive z direction. When viewed from a pointon the positive z axis, it subsequent motion is:

A. straight aheadB. counterclockwise around a circle in the xy planeC. clockwise around a circle in the xy planeD. in the positive z directionE. in the negative z direction

ans: B

18. A uniform magnetic eld is directed into the page. A charged particle, moving in the plane ofthe page, follows a clockwise spiral of decreasing radius as shown. A reasonable explanation is:

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particle

nB

A. the charge is positive and slowing downB. the charge is negative and slowing downC. the charge is positive and speeding upD. the charge is negative and speeding upE. none of the above

ans: B


19. An electron and a proton each travel with equal speeds around circular orbits in the sameuniform magnetic eld, as shown in the diagram (not to scale). The eld is into the page onthe diagram. Because the electron is less massive than the proton and because the electron isnegatively charged and the proton is positively charged:

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nB

A. the electron travels clockwise around the smaller circle and the proton travels counter-clockwise around the larger circle

B. the electron travels counterclockwise around the smaller circle and the proton travels clock-wise around the larger circle

C. the electron travels clockwise around the larger circle and the proton travels counterclock-wise around the smaller circle

D. the electron travels counterclockwise around the larger circle and the proton travels clock-wise around the smaller circle

E. the electron travels counterclockwise around the smaller circle and the proton travels coun-terclockwise around the larger circle

ans: A

20. An electron is launched with velocity nv in a uniform magnetic eld nB. The angle betweennv and nB is between 0 and 90H. As a result, the electron follows a helix, its velocity vector nvreturning to its initial value in a time interval of:

A. 2$m/eBB. 2$mv/eBC. 2$mv sin /eBD. 2$mv cos /eBE. none of these

ans: A

21. An electron and a proton are both initially moving with the same speed and in the samedirection at 90H to the same uniform magnetic eld. They experience magnetic forces, whichare initially:

A. identicalB. equal in magnitude but opposite in directionC. in the same direction and di&ering in magnitude by a factor of 1840D. in opposite directions and di&ering in magnitude by a factor of 1840E. equal in magnitude but perpendicular to each other.

ans: B


22. An electron enters a region of uniform perpendicular nE and nB elds. It is observed that thevelocity nv of the electron is una&ected. A possible explanation is:

A. nv is parallel to nE and has magnitude E/BB. nv is parallel to nBC. nv is perpendicular to both nE and nB and has magnitude B/ED. nv is perpendicular to both nE and nB and has magnitude E/BE. the given situation is impossible

ans: D

23. A charged particle is projected into a region of uniform, parallel, nE and nB elds. The force onthe particle is:

A. zeroB. at some angle < 90H with the eld linesC. along the eld linesD. perpendicular to the eld linesE. unknown (need to know the sign of the charge)

ans: B

24. A uniform magnetic eld is in the positive z direction. A positively charged particle is movingin the positive x direction through the eld. The net force on the particle can be made zeroby applying an electric eld in what direction?

A. Positive yB. Negative yC. Positive xD. Negative xE. Positive z

ans: B

25. An electron is traveling in the positive x direction. A uniform electric eld nE is in the negativey direction. If a uniform magnetic eld with the appropriate magnitude and direction alsoexists in the region, the total force on the electron will be zero. The appropriate direction forthe magnetic eld is:

x

y

................................................................................ ......................nv..........................................................................

............................ nE

A. the positive y directionB. the negative y directionC. into the pageD. out of the pageE. the negative x direction

ans: C


26. An ion with a charge of +3.21019 C is in a region where a uniform electric eld of 5104V/mis perpendicular to a uniform magnetic eld of 0.8T. If its acceleration is zero then its speedmust be:

A. 0B. 1.6 104m/sC. 4.0 104m/sD. 6.3 104m/sE. any value but 0

ans: D

27. The current is from left to right in the conductor shown. The magnetic eld is into the pageand point S is at a higher potential than point T. The charge carriers are:

S

T

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i

A. positiveB. negativeC. neutralD. absentE. moving near the speed of light

ans: A

28. Electrons (mass m, charge e) are accelerated from rest through a potential di&erence V andare then deected by a magnetic eld nB that is perpendicular to their velocity. The radius ofthe resulting electron trajectory is:

A. (02eV/m)/B

B. B$2eV /m

C. (02mV/e)/B

D. B$2mV /e

E. none of these

ans: C

29. In a certain mass spectrometer, an ion beam passes through a velocity lter consisting ofmutually perpendicular elds nE and nB. The beam then enters a region of another magneticeld nBI perpendicular to the beam. The radius of curvature of the resulting ion beam isproportional to:

A. EBI/BB. EB/BI

C. BBI/ED. B/EBI

E. E/BBI

ans: E


30. A cyclotron operates with a given magnetic eld and at a given frequency. If R denotes theradius of the nal orbit, the nal particle energy is proportional to:

A. 1/RB. RC. R2

D. R3

E. R4

ans: C

31. J. J. Thomsons experiment, involving the motion of an electron beam in mutually perpendic-ular nE and nB elds, gave the value of:

A. mass of an electronB. charge of an electronC. Earths magnetic eldD. charge/mass ratio for electronsE. Avogadros number

ans: D

32. The diagram shows a straight wire carrying a ow of electrons into the page. The wire isbetween the poles of a permanent magnet. The direction of the magnetic force exerted on thewire is:

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.......................................................................................N S

A. B. C.

D. E. into the page

ans: A


33. The gure shows the motion of electrons in a wire that is near the N pole of a magnet. Thewire will be pushed:

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A. toward the magnetB. away from the magnetC. downwardsD. upwardsE. along its length

ans: D

34. The diagram shows a straight wire carrying current i in a uniform magnetic eld. The magneticforce on the wire is indicated by an arrow but the magnetic eld is not shown. Of the followingpossibilities, the direction of the magnetic eld is:

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...i

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nF

A. opposite the direction of the currentB. opposite the direction of nFC. in the direction of nFD. into the pageE. out of the page

ans: E


35. The gure shows a uniform magnetic eld nB directed to the left and a wire carrying a currentinto the page. The magnetic force acting on the wire is:

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nB

i

A. toward the top of the pageB. toward the bottom of the pageC. toward the leftD. toward the rightE. zero

ans: A

36. A loop of wire carrying a current of 2.0A is in the shape of a right triangle with two equal sides,each 15 cm long. A 0.7T uniform magnetic eld is parallel to the hypotenuse. The resultantmagnetic force on the two equal sides has a magnitude of:

A. 0B. 0.21NC. 0.30ND. 0.41NE. 0.51N

ans: A

37. A loop of wire carrying a current of 2.0A is in the shape of a right triangle with two equalsides, each 15 cm long. A 0.7T uniform magnetic eld is in the plane of the triangle and isperpendicular to the hypotenuse. The magnetic force on either of the two equal sides has amagnitude of:

A. zeroB. 0.105NC. 0.15ND. 0.21NE. 0.25N

ans: C

38. A current is clockwise around the outside edge of this page and a uniform magnetic eld isdirected parallel to the page, from left to right. If the magnetic force is the only force actingon the page, the page will turn so the right edge:

A. moves toward youB. moves away from youC. moves to your rightD. moves to your leftE. does not move

ans: A


39. A square loop of wire lies in the plane of the page and carries a current I as shown. There is auniform magnetic eld nB parallel to the side MK as indicated. The loop will tend to rotate:

M

P

KR

L

Q

NS

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nB

A. about PQ with KL coming out of the pageB. about PQ with KL going into the pageC. about RS with MK coming out of the pageD. about RS with MK going into the pageE. about an axis perpendicular to the page.

ans: A

40. The units of magnetic dipole moment are:

A. ampereB. amperemeterC. amperemeter2D. ampere/meterE. ampere/meter2

ans: C

41. You are facing a loop of wire which carries a clockwise current of 3.0A and which surroundsan area of 5.8 102m2. The magnetic dipole moment of the loop is:A. 3.0A m2, away from youB. 3.0A m2, toward youC. 0.17A m2, away from youD. 0.17A m2, toward youE. 0.17A m2, left to right

ans: C

42. The magnetic torque exerted on a at current-carrying loop of wire by a uniform magneticeld nB is:

A. maximum when the plane of the loop is perpendicular to nBB. maximum when the plane of the loop is parallel to nBC. dependent on the shape of the loop for a xed loop areaD. independent of the orientation of the loopE. such as to rotate the loop around the magnetic eld lines

ans: B


43. A circular loop of wire with a radius of 20 cm lies in the xy plane and carries a current of 2A,counterclockwise when viewed from a point on the positive z axis. Its magnetic dipole momentis:

A. 0.25A m2, in the positive z directionB. 0.25A m2, in the negative z directionC. 2.5A m2, in the positive z directionD. 2.5A m2, in the negative z directionE. 0.25A m2, in the xy plane

ans: A

44. The diagrams show ve possible orientations of a magnetic dipole n in a uniform magnetic eldnB. For which of these does the magnetic torque on the dipole have the greatest magnitude?

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.... nB.....................................................................................................................n

A

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.... nB............................................................................................... ......................n

B

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C

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.... nB.....................................................................................................................n

D

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.... nB.....................................................................................................................n

E

ans: A

45. The magnetic dipole moment of a current-carrying loop of wire is in the positive z direction.If a uniform magnetic eld is in the positive x direction the magnetic torque on the loop is:

A. 0B. in the positive y directionC. in the negative y directionD. in the positive z directionE. in the negative z direction

ans: B

46. For a loop of current-carrying wire in a uniformmagnetic eld the potential energy is a minimumif the magnetic dipole moment of the loop is:

A. in the same direction as the eldB. in the direction opposite to that of the eldC. perpendicular to the eldD. at an angle of 45H to the eldE. none of the above

ans: A

47. The diagrams show ve possible orientations of a magnetic dipole n in a uniform magnetic eldnB. For which of these is the potential energy the greatest?

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.... nB.....................................................................................................................n

A

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.... nB............................................................................................... ......................n

B

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.... nB.....................................................................................................................n

C

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.... nB.....................................................................................................................n

D

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.... nB.....................................................................................................................n

E

ans: E


48. A loop of current-carrying wire has a magnetic dipole moment of 5104 A m2. The momentinitially is aligned with a 0.5-T magnetic eld. To rotate the loop so its dipole moment isperpendicular to the eld and hold it in that orientation, you must do work of:

A. 0B. 2.5 104 JC. 2.5 104 JD. 1.0 103 JE. 1.0 103 J

ans: B


Chapter 29: MAGNETIC FIELDS DUE TO CURRENTS

1. Suitable units for 0 are:

A. teslaB. newton/ampere2

C. weber/meterD. kilogramampere/meterE. teslameter/ampere

ans: E

2. A coulomb is:

A. one ampere per secondB. the quantity of charge that will exert a force of 1N on a similar charge at a distance of 1mC. the amount of current in each of two long parallel wires, separated by 1m, that produces

a force of 2 107N/mD. the amount of charge that ows past a point in one second when the current is 1AE. an abbreviation for a certain combination of kilogram, meter and second

ans: D

3. Electrons are going around a circle in a counterclockwise direction as shown. At the center ofthe circle they produce a magnetic eld that is:

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electron

A. into the pageB. out of the pageC. to the leftD. to the rightE. zero

ans: A

418 Chapter 29: MAGNETIC FIELDS DUE TO CURRENTS

4. In the gure, the current element idnf, the point P, and the three vectors (1, 2, 3) are all in theplane of the page. The direction of d nB, due to this current element, at the point P is:

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P

1

2

3

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A. in the direction marked 1B. in the direction marked 2C. in the direction marked 3D. out of the pageE. into the page

ans: E

5. The magnitude of the magnetic eld at point P, at the center of the semicircle shown, is givenby:

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R P

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A. 20i/RB. 0i/RC. 0i/4$RD. 0i/2RE. 0i/4R

ans: E

Chapter 29: MAGNETIC FIELDS DUE TO CURRENTS 419

6. The diagrams show three circuits consisting of concentric circular arcs (either half or quartercircles of radii r, 2r, and 3r) and radial lengths. The circuits carry the same current. Rankthem according to the magnitudes of the magnetic elds they produce at C, least to greatest.

C..........................................................................................................................

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C

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3

A. 1, 2, 3B. 3, 2, 1C. 1, 3, 2D. 2, 3, 1E. 2, 1, 3

ans: B

7. Lines of the magnetic eld produced by a long straight wire carrying a current are:

A. in the direction of the currentB. opposite to the direction of the currentC. radially outward from the wireD. radially inward toward the wireE. circles that are concentric with the wire

ans: E

8. In an overhead straight wire, the current is north. The magnetic eld due to this current, atour point of observation, is:

A. eastB. upC. northD. downE. west

ans: E

9. A wire carrying a large current i from east to west is placed over an ordinary magnetic compass.The end of the compass needle marked N will point:

A. northB. southC. eastD. westE. the compass will act as an electric motor, hence the needle will keep rotating

ans: B


10. The magnetic eld outside a long straight current-carrying wire depends on the distance Rfrom the wire axis according to:

A. RB. 1/RC. 1/R2

D. 1/R3

E. 1/R3/2

ans: B

11. Which graph correctly gives the magnitude of the magnetic eld outside an innitely longstraight current-carrying wire as a function of the distance r from the wire?

B

r

A

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r

B

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B

r

C

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B

r

D

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B

r

E

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ans: D

12. The magnetic eld a distance 2 cm from a long straight current-carrying wire is 2.0 105 T.The current in the wire is:

A. 0.16AB. 1.0AC. 2.0AD. 4.0AE. 25A

ans: C

13. Two long parallel straight wires carry equal currents in opposite directions. At a point midwaybetween the wires, the magnetic eld they produce is:

A. zeroB. non-zero and along a line connecting the wiresC. non-zero and parallel to the wiresD. non-zero and perpendicular to the plane of the two wiresE. none of the above

ans: D


14. Two long straight wires are parallel and carry current in the same direction. The currents are8.0 and 12A and the wires are separated by 0.40 cm. The magnetic eld in tesla at a pointmidway between the wires is:

A. 0B. 4.0 104C. 8.0 104D. 12 104E. 20 104

ans: B

15. Two long straight wires are parallel and carry current in opposite directions. The currents are8.0 and 12A and the wires are separated by 0.40 cm. The magnetic eld in tesla at a pointmidway between the wires is:

A. 0B. 4.0 104C. 8.0 104D. 12 104E. 20 104

ans: E

16. Two long straight current-carrying parallel wires cross the x axis and carry currents I and 3Iin the same direction, as shown. At what value of x is the net magnetic eld zero?

x

0 1 3 4 5 7

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I ...................................................................

3I

A. 0B. 1C. 3D. 5E. 7

ans: C


17. Two long straight wires pierce the plane of the paper at vertices of an equilateral triangle asshown below. They each carry 2A, out of the paper. The magnetic eld at the third vertex(P) has magnitude (in T):

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P

2A 2A

4 cm 4 cm

4 cm

A. 1.0 105B. 1.7 105C. 2.0 105D. 5.0 106E. 8.7 106

ans: B

18. The diagram shows three equally spaced wires that are perpendicular to the page. The currentsare all equal, two being out of the page and one being into the page. Rank the wires accordingto the magnitudes of the magnetic forces on them, from least to greatest.

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........................................ 1 2 3

A. 1, 2, 3B. 2, 1 and 3 tieC. 2 and 3 tie, then 1D. 1 and 3 tie, then 2E. 3, 2, 1

ans: B

19. Two parallel wires carrying equal currents of 10A attract each other with a force of 1mN. Ifboth currents are doubled, the force of attraction will be:

A. 1mNB. 4mNC. 0.5mND. 0.25mNE. 2mN

ans: B


20. Two parallel long wires carry the same current and repel each other with a force F per unitlength. If both these currents are doubled and the wire separation tripled, the force per unitlength becomes:

A. 2F/9B. 4F/9C. 2F/3D. 4F/3E. 6F

ans: D

21. Two parallel wires, 4 cm apart, carry currents of 2A and 4A respectively, in the same direction.The force per unit length in N/m of one wire on the other is:

A. 1 103, repulsiveB. 1 103, attractiveC. 4 105, repulsiveD. 4 105, attractiveE. none of these

ans: D

22. Two parallel wires, 4 cm apart, carry currents of 2A and 4A respectively, in opposite directions.The force per unit length in N/m of one wire on the other is:

A. 1 103, repulsiveB. 1 103, attractiveC. 4 105, repulsiveD. 4 105, attractiveE. none of these

ans: C

23. Four long straight wires carry equal currents into the page as shown. The magnetic forceexerted on wire F is:

W E

N

SF

A. northB. eastC. southD. westE. zero

ans: B


24. A constant current is sent through a helical coil. The coil:

A. tends to get shorterB. tends to get longerC. tends to rotate about its axisD. produces zero magnetic eld at its centerE. none of the above

ans: A

25. The diagram shows three arrangements of circular loops, centered on vertical axes and car-rying identical currents in the directions indicated. Rank the arrangements according to themagnitudes of the magnetic elds at the midpoints between the loops on the central axes.

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1

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2

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3

A. 1, 2, 3B. 2, 1, 3C. 2, 3, 1D. 3, 2, 1E. 3, 1, 2

ans: C

26. Helmholtz coils are commonly used in the laboratory because the magnetic eld between them:

A. can be varied more easily than the elds of other current arrangementsB. is especially strongC. nearly cancels Earths magnetic eldD. is parallel to the plane of the coilsE. is nearly uniform

ans: E

27. If the radius of a pair of Helmholtz coils is R then the distance between the coils is:

A. R/4B. R/2C. RD. 2RE. 4R

ans: C


28. If R is the distance from a magnetic dipole, then the magnetic eld it produces is proportionalto:

A. RB. 1/RC. R2

D. 1/R2

E. 1/R3

ans: E

29. A square loop of current-carrying wire with edge length a is in the xy plane, the origin beingat its center. Along which of the following lines can a charge move without experiencing amagnetic force?

A. x = 0, y = a/2B. x = a/2, y = a/2C. x = a/2, y = 0D. x = 0, y = 0E. x = 0, z = 0

ans: D

30. In Amperes law,

nB dns = 0i, the integration must be over any:

A. surfaceB. closed surfaceC. pathD. closed pathE. closed path that surrounds all the current producing nB

ans: D

31. In Amperes law,

nB dns = 0i, the symbol dns is:

A. an innitesimal piece of the wire that carries current iB. in the direction of nBC. perpendicular to nBD. a vector whose magnitude is the length of the wire that carries current iE. none of the above

ans: E

32. In Amperes law,

nB dns = 0i, the direction of the integration around the path:

A. must be clockwiseB. must be counterclockwiseC. must be such as to follow the magnetic eld linesD. must be along the wire in the direction of the currentE. none of the above

ans: E


33. A long straight wire carrying a 3.0A current enters a room through a window 1.5m high and1.0m wide. The path integral

nB dns around the window frame has the value (in Tm):

A. 0.20B. 2.5 107C. 3.0 107D. 3.8 106E. none of these

ans: D

34. Two long straight wires enter a room through a door. One carries a current of 3.0A into theroom while the other carries a current of 5.0A out. The magnitude of the path integral

nB dns

around the door frame is:

A. 2.5 106 T mB. 3.8 106 T mC. 6.3 106 T mD. 1.0 105 T mE. none of these

ans: A

35. If the magnetic eld nB is uniform over the area bounded by a circle with radius R, the netcurrent through the circle is:

A. 0B. 2$RB/0C. $R2B/0D. RB/20E. 2RB/0

ans: A

36. The magnetic eld at any point is given by nB = Anr k, where nr is the position vector of thepoint and A is a constant. The net current through a circle of radius R, in the xy plane andcentered at the origin is given by:

A. $AR2/0B. 2$AR/0C. 4$AR3/30D. 2$AR2/0E. $AR2/20

ans: D


37. A hollow cylindrical conductor (inner radius = a, outer radius = b) carries a current i uniformlyspread over its cross section. Which graph below correctly gives B as a function of the distancer from the center of the cylinder?

a br

B

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A

a br

B..........................................................................................................................................................................................................................

B

a br

B

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C

a br

B

...............................................................................................................................................................................................................................................................................................................................

D

a br

B

..........................................................................................................................................................................................................................................................................................................................................................................................................................

E

ans: C

38. A long straight cylindrical shell carries current i parallel to its axis and uniformly distributedover its cross section. The magnitude of the magnetic eld is greatest:

A. at the inner surface of the shellB. at the outer surface of the shellC. inside the shell near the middleD. in hollow region near the inner surface of the shellE. near the center of the hollow region

ans: B

39. A long straight cylindrical shell has inner radius Ri and outer radius Ro. It carries currenti, uniformly distributed over its cross section. A wire is parallel to the cylinder axis, in thehollow region (r < Ri). The magnetic eld is zero everywhere outside the shell (r > Ro). Weconclude that the wire:

A. is on the cylinder axis and carries current i in the same direction as the current in the shellB. may be anywhere in the hollow region but must be carrying current i in the direction

opposite to that of the current in the shellC. may be anywhere in the hollow region but must be carrying current i in the same direction

as the current in the shellD. is on the cylinder axis and carries current i in the direction opposite to that of the current

in the shellE. does not carry any current

ans: D


40. A long straight cylindrical shell has inner radius Ri and outer radius Ro. It carries a current i,uniformly distributed over its cross section. A wire is parallel to the cylinder axis, in the hollowregion (r < Ri). The magnetic eld is zero everywhere in the hollow region. We conclude thatthe wire:

A. is on the cylinder axis and carries current i in the same direction as the current in the shellB. may be anywhere in the hollow region but must be carrying current i in the direction

opposite to that of the current in the shellC. may be anywhere in the hollow region but must be carrying current i in the same direction

as the current in the shellD. is on the cylinder axis and carries current i in the direction opposite to that of the current

in the shellE. does not carry any current

ans: E

41. The magnetic eld B inside a long ideal solenoid is independent of:

A. the currentB. the core materialC. the spacing of the windingsD. the cross-sectional area of the solenoidE. the direction of the current

ans: D

42. Two long ideal solenoids (with radii 20mm and 30mm, respectively) have the same numberof turns of wire per unit length. The smaller solenoid is mounted inside the larger, along acommon axis. The magnetic eld within the inner solenoid is zero. The current in the innersolenoid must be:

A. two-thirds the current in the outer solenoidB. one-third the current in the outer solenoidC. twice the current in the outer solenoidD. half the current in the outer solenoidE. the same as the current in the outer solenoid

ans: E

43. Magnetic eld lines inside the solenoid shown are:

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...

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I...........................................................................................

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I

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A. clockwise circles as one looks down the axis from the top of the pageB. counterclockwise circles as one looks down the axis from the top of the pageC. toward the top of the pageD. toward the bottom of the pageE. in no direction since B = 0

ans: C


44. Solenoid 2 has twice the radius and six times the number of turns per unit length as solenoid1. The ratio of the magnetic eld in the interior of 2 to that in the interior of 1 is:

A. 2B. 4C. 6D. 1E. 1/3

ans: C

45. A solenoid is 3.0 cm long and has a radius of 0.50 cm. It is wrapped with 500 turns of wirecarrying a current of 2.0A. The magnetic eld at the center of the solenoid is:

A. 9.9 108 TB. 1.3 103 TC. 4.2 102 TD. 16TE. 20T

ans: C

46. A toroid with a square cross section carries current i. The magnetic eld has its largestmagnitude:

A. at the center of the holeB. just inside the toroid at its inner surfaceC. just inside the toroid at its outer surfaceD. at any point inside (the eld is uniform)E. none of the above

ans: B

47. A toroid has a square cross section with the length of an edge equal to the radius of the innersurface. The ratio of the magnitude of the magnetic eld at the inner surface to the magnitudeof the eld at the outer surface is:

A. 1/4B. 1/2C. 1D. 2E. 4

ans: D


Chapter 30: INDUCTION AND INDUCTANCE

1. The normal to a certain 1-m2 area makes an angle of 60H with a uniform magnetic eld.The magnetic ux through this area is the same as the ux through a second area that isperpendicular to the eld if the second area is:

A. 0.866m2

B. 1.15m2

C. 0.5m2

D. 2m2

E. 1m2

ans: C

2. Suppose this page is perpendicular to a uniform magnetic eld and the magnetic ux throughit is 5Wb. If the page is turned by 30H around an edge the ux through it will be:

A. 2.5WbB. 4.3WbC. 5WbD. 5.8WbE. 10Wb

ans: B

3. A 2-T uniform magnetic eld makes an angle of 30H with the z axis. The magnetic ux througha 3-m2 portion of the xy plane is:

A. 2.0WbB. 3.0WbC. 5.2WbD. 6.0WbE. 12Wb

ans: C

4. A uniform magnetic eld makes an angle of 30H with the z axis. If the magnetic ux througha 1-m2 portion of the xy plane is 5Wb then the magnetic ux through a 2-m2 portion of thesame plane is:

A. 2.5WbB. 4.3WbC. 5WbD. 5.8WbE. 10Wb

ans: E

5. 1weber is the same as:

A. 1V/sB. 1T/sC. 1T/mD. 1T m2E. 1T/m

2

ans: D

Chapter 30: INDUCTION AND INDUCTANCE 431

6. 1weber is the same as:

A. 1V sB. 1T sC. 1T/mD. 1V/s

E. 1T/m2

ans: A

7. The units of motional emf are:

A. volt/secondB. voltmeter/secondC. volt/teslaD. tesla/secondE. teslameter2/second

ans: E

8. Faradays law states that an induced emf is proportional to:

A. the rate of change of the magnetic eldB. the rate of change of the electric eldC. the rate of change of the magnetic uxD. the rate of change of the electric uxE. zero

ans: C

9. The emf that appears in Faradays law is:

A. around a conducting circuitB. around the boundary of the surface used to compute the magnetic uxC. throughout the surface used to compute the magnetic uxD. perpendicular to the surface used to compute the magnetic uxE. none of the above

ans: B

10. If the magnetic ux through a certain region is changing with time:

A. energy must be dissipated as heatB. an electric eld must exist at the boundaryC. a current must ow around the boundaryD. an emf must exist around the boundaryE. a magnetic eld must exist at the boundary

ans: D

432 Chapter 30: INDUCTION AND INDUCTANCE

11. A square loop of wire lies in the plane of the page. A decreasing magnetic eld is directed intothe page. The induced current in the loop is:

A. counterclockwiseB. clockwiseC. zeroD. up the left edge and from right to left along the top edgeE. through the middle of the page

ans: B

12. As an externally generated magnetic eld through a certain conducting loop increases in mag-nitude, the eld produced at points inside the loop by the current induced in the loop mustbe:

A. increasing in magnitudeB. decreasing in magnitudeC. in the same direction as the applied eldD. directed opposite to the applied eldE. perpendicular to the applied eld

ans: D

13. At any instant of time the total magnetic ux through a stationary conducting loop is less inmagnitude than the ux associated with an externally applied eld. This might occur because:

A. the applied eld is normal to the loop and increasing in magnitudeB. the applied eld is normal to the loop and decreasing in magnitudeC. the applied eld is parallel to the plane of the loop and increasing in magnitudeD. the applied eld is parallel to the plane of the loop and decreasing in magnitudeE. the applied eld is tangent to the loop

ans: A

14. A long straight wire is in the plane of a rectangular conducting loop. The straight wire carriesa constant current i, as shown. While the wire is being moved toward the rectangle the currentin the rectangle is:

.........................

......................i

A. zeroB. clockwiseC. counterclockwiseD. clockwise in the left side and counterclockwise in the right sideE. counterclockwise in the left side and clockwise in the right side

ans: C


15. A long straight wire is in the plane of a rectangular conducting loop. The straight wire carriesan increasing current in the direction shown. The current in the rectangle is:

.........................

......................i


ans: C

16. A long straight wire is in the plane of a rectangular conducting loop. The straight wire initiallycarries a constant current i in the direction shown. While the current i is being shut o&, thecurrent in the rectangle is:

.........................

......................i


ans: B


17. A rectangular loop of wire is placed midway between two long straight parallel conductors asshown. The conductors carry currents i1 and i2, as indicated. If i1 is increasing and i2 isconstant, then the induced current in the loop is:

...........................

......................i1...........................

...................... i2

A. zeroB. clockwiseC. counterclockwiseD. depends on i1 i2E. depends on i1 + i2

ans: C

18. You push a permanent magnet with its north pole away from you toward a loop of conductingwire in front of you. Before the north pole enters the loop the current in the loop is:

A. zeroB. clockwiseC. counterclockwiseD. to your leftE. to your right

ans: C

19. A vertical bar magnet is dropped through the center of a horizontal loop of wire, with its northpole leading. At the instant when the midpoint of the magnet is in the plane of the loop, theinduced current at point P, viewed from above, is:

A. maximum and clockwiseB. maximum and counterclockwiseC. not maximum but clockwiseD. not maximum but counterclockwiseE. essentially zero

ans: E

20. A circular loop of wire rotates about a diameter in a magnetic eld that is perpendicular tothe axis of rotation. Looking in the direction of the eld at the loop the induced current is:

A. always clockwiseB. always counterclockwiseC. clockwise in the lower half of the loop and counterclockwise in the upper halfD. clockwise in the upper half of the loop and counterclockwise in the lower halfE. sometimes clockwise and sometimes counterclockwise

ans: E


21. In the experiment shown:

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S

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G

A. there is a steady reading in G as long as S is closedB. a motional emf is generated when S is closedC. the current in the battery goes through GD. there is a current in G just after S is opened or closedE. since the two loops are not connected, the current in G is always zero

ans: D

22. The emf developed in a coil X due to the current in a neighboring coil Y is proportional to the:

A. magnetic eld in XB. rate of change of magnetic eld in XC. resistance of XD. thickness of the wire in XE. current in Y

ans: B

23. One hundred turns of insulated copper wire are wrapped around an iron core of cross-sectionalarea 0.100m2. The circuit is completed by connecting the coil to a 10- resistor. As themagnetic eld along the coil axis changes from 1.00T in one direction to 1.00T in the otherdirection, the total charge that ows through the resistor is:

A. 102 CB. 2 102 CC. 1CD. 2CE. 0.20C

ans: D


24. In the circuit shown, there will be a non-zero reading in galvanometer G:

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G

A. only just after S is closedB. only just after S is openedC. only while S is kept closedD. neverE. only just after S is opened or closed

ans: E

25. A magnet moves inside a coil. Consider the following factors:

I. strength of the magnetII. number of turns in the coilIII. speed at which the magnet moves

Which can a&ect the emf induced in the coil?

A. I onlyB. II onlyC. III onlyD. I and II onlyE. I, II, III

ans: E

26. The graph shows the magnitude B of a uniform magnetic eld that is perpendicular to theplane of a conducting loop. Rank the ve regions indicated on the graph according to themagnitude of the emf induced in the loop, from least to greatest.

1

2

3

4

t

B

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A. 1, 2, 3, 4B. 2, 4, 3, 1C. 4, 3, 1, 2D. 1, 3, 4, 2E. 4, 3, 2, 1

ans: B


27. The circuit shown is in a uniform magnetic eld that is into the page. The current in the circuitis 0.20A. At what rate is the magnitude of the magnetic eld changing? Is it increasing ordecreasing?:

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4V

10

12 cm

||12 cm

||

A. zeroB. 140T/s, decreasingC. 140T/s, increasingD. 420T/s, decreasingE. 420T/s, increasing

ans: B

28. A changing magnetic eld pierces the interior of a circuit containing three identical resistors.Two voltmeters are connected to the same points, as shown. V1 reads 1mV. V2 reads:

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.......

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R R

R

A. 0B. 1/3mVC. 1/2mVD. 1mVE. 2mV

ans: E


29. A circular loop of wire is positioned half in and half out of a square region of constant uniformmagnetic eld directed into the page, as shown. To induce a clockwise current in this loop:

nB

loop

x

y

A. move it in +x directionB. move it in +y directionC. move it in y directionD. move it in x directionE. increase the strength of the magnetic eld

ans: A

30. The four wire loops shown have edge lengths of either L, 2L, or 3L. They will move with thesame speed into a region of uniform magnetic eld nB, directed out of the page. Rank themaccording to the maximum magnitude of the induced emf, least to greatest.

1 2 3 4

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.........

. . . . .. . . .

. . . . .. . . .

. . . . .. . . .

. . . . .. . . .

. . . . .. . . .

. . . . .

A. 1 and 2 tie, then 3 and 4 tieB. 3 and 4 tie, then 1 and 2 tieC. 4, 2, 3, 1D. 1, then 2 and 3 tie, then 4E. 1, 2, 3, 4

ans: D


31. A square loop of wire moves with a constant speed v from a eld-free region into a regionof constant uniform magnetic eld, as shown. Which of the ve graphs correctly shows theinduced current i in the loop as a function of time t?

nB............................................................................................... ......................

nv

t

i

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A

t

i

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t

i

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C

t

i

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D

t

i

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E

ans: C

32. The gure shows a bar moving to the right on two conducting rails. To make an inducedcurrent i in the direction indicated, a constant magnetic eld in region A should be in whatdirection?

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i

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i

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i

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i ............................................................................................... ......................

nvA

A. RightB. LeftC. Into the pageD. Out of the pageE. Impossible; this cannot be done with a constant magnetic eld

ans: C


33. A car travels northward at 75 km/h along a straight road in a region where Earths magneticeld has a vertical component of 0.50 104 T. The emf induced between the left and rightside, separated by 1.7m, is:

A. 0B. 1.8mVC. 3.6mVD. 6.4mVE. 13mV

ans: B

34. Coils P and Q each have a large number of turns of insulated wire. When switch S is closed,the pointer of galvanometer G is deected toward the left. With S now closed, to make thepointer of G deect toward the right one could:

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P

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Q

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S

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R

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................................................ G

A. move the slide of the rheostat R quickly to the rightB. move coil P toward coil QC. move coil Q toward coil PD. open SE. do none of the above

ans: D

35. A rod lies across frictionless rails in a constant uniform magnetic eld nB, as shown. Therod moves to the right with speed v. In order for the emf around the circuit to be zero, themagnitude of the magnetic eld should:

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nv

A. not changeB. increase linearly with timeC. decrease linearly with timeD. increase quadratically with timeE. decrease quadratically with time

ans: C


36. A rectangular loop of wire has area A. It is placed perpendicular to a uniform magnetic eldB and then spun around one of its sides at frequency f . The maximum induced emf is:

A. BAfB. BAfC. 2BAfD. 2$BAfE. 4$BAf

ans: D

37. A rectangular loop of wire is placed perpendicular to a uniform magnetic eld and then spunaround one of its sides at frequency f . The induced emf is a maximum when:

A. the ux is zeroB. the ux is a maximumC. the ux is half its maximum valueD. the derivative of the ux with respect to time is zeroE. none of the above

ans: A

38. The diagram shows a circular loop of wire that rotates at a steady rate about a diameter Othat is perpendicular to a uniform magnetic eld. The maximum induced emf occurs when thepoint X on the loop passes:

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test 3 test bank physics 2

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