Question 1

A toroid with a square cross section carries current i.The magnetic field has its largest magnitude:

Accepted Answer

A)  at the center of the hole
B)  just inside the toroid at its inner surface
C)  just inside the toroid at its outer surface
D)  at any point inside (the field is uniform) 
E)  at none of the aboveF) A) and E)
G) A) and B)

Question 2

Two long parallel straight wires carry equal currents in opposite directions.At a point midway between the wires, the magnetic field they produce is:

Accepted Answer

A)  zero
B)  non-zero and along a line connecting the wires
C)  non-zero and parallel to the wires
D)  non-zero and perpendicular to the plane of the two wires
E)  none of the aboveF) A) and E)
G) None of the above

Question 3

The magnetic field outside a long straight current-carrying wire depends on the distance R from the wire axis according to:

Accepted Answer

A)  R
B)  1/R
C)  1/R2
D)  1/R3
E)  1/R3/2F) A) and B)
G) A) and C)

Question 4

Lines of the magnetic field produced by a long straight wire carrying a current are:

Accepted Answer

A)  in the direction of the current
B)  opposite to the direction of the current
C)  leave the wire radially
D)  circles concentric with the wire
E)  lines similar to those produced by a bar magnetF) B) and D)
G) B) and C)

Question 5

Suitable units for  μ\muμ 0 are:

Accepted Answer

A)  tesla
B)  newton/ampere2
C)  weber/meter
D)  kilogram.ampere/meter
E)  tesla.meter/ampere F) D) and E)
G) A) and D)

Question 6

The diagram shows three arrangements of circular loops, centered on vertical axes and carrying identical currents in the directions indicated.Rank the arrangements according to the magnitudes of the magnetic fields at the midpoints between the loops on the central axes, from least to greatest.

Accepted Answer

A)  1, 2, 3
B)  2, 1, 3
C)  2, 3, 1
D)  3, 2, 1
E)  3, 1, 2F) A) and B)
G) C) and E)

Question 7

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

Accepted Answer

A)  2F/9
B)  4F/9
C)  2F/3
D)  4F/3
E)  6FF) A) and B)
G) All of the above

Question 8

The magnitude of the magnetic field at point P, at the center of the semicircle shown, is given by: 0i/R2  B)   \mu 0i/2 \pi R  C)   \mu 0i/4 \pi R  D)   \mu 0i/2R  E)   \mu 0i/4R  " class="answers-bank-image d-inline" rel="preload" >

Accepted Answer

A)  "2 μ\muμ 0i/R2"
B)  " μ\muμ 0i/2 π\piπ R"
C)  " μ\muμ 0i/4 π\piπ R"
D)  " μ\muμ 0i/2R"
E)  " μ\muμ 0i/4R" F) A) and E)
G) All of the above

Question 9

In an overhead straight wire, the current is north.The magnetic field due to this current, at our point of observation, is:

Accepted Answer

A)  east
B)  up
C)  north
D)  down
E)  westF) D) and E)
G) B) and D)

Question 10

The magnetic field at any point in the xy plane is given by , where is the position vector of the point, A is a constant, and is a unit vector in the +z direction.The net current through a circle of radius R, in the xy plane and centered at the origin is given by:

Accepted Answer

A)  "  π\piπ AR2/ μ\muμ 0"
B)  "2  π\piπ AR/ μ\muμ 0"
C)  "4  π\piπ AR3/3 μ\muμ 0"
D)  "2  π\piπ AR2/ μ\muμ 0"
E)  "  π\piπ AR2/2 μ\muμ 0" F) C) and E)
G) A) and C) D

Question 11

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

Accepted Answer

A)  is on the cylinder axis and carries current i in the same direction as the current in the shell
B)  may be anywhere in the hollow region but must be carrying current i in the direction opposite to that of the current in the shell
C)  may be anywhere in the hollow region but must be carrying current i in the same direction as the current in the shell
D)  is on the cylinder axis and carries current i in the direction opposite to that of the current in the shell
E)  does not carry any currentF) B) and D)
G) C) and D)

Question 12

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

Accepted Answer

A)  1/3
B)  1
C)  2
D)  4
E)  6F) A) and B)
G) D) and E) E

Question 13

Two long straight wires pierce the plane of the paper at vertices of an equilateral triangle as shown below.They each carry 2.0 A, out of the paper.The magnetic field at the third vertex (P) has magnitude: -6 T B) 8.7 * 10-6 T C) 1.0 * 10-5 T D) 1.7 * 10-5 T E) 2.0 *10-5 T" class="answers-bank-image d-inline" rel="preload" >

Accepted Answer

A)  5.0 * 10-6 T
B)  8.7 * 10-6 T
C)  1.0 * 10-5 T
D)  1.7 * 10-5 T
E)  2.0 *10-5 TF) B) and E)
G) None of the above

Question 14

In the figure, the current element , the point P, and the three vectors (1, 2, 3) are all in the plane of the page.The direction of , due to this current element, at the point P is:

Accepted Answer

A)  in the direction marked "1"
B)  in the direction marked "2"
C)  in the direction marked "3"
D)  out of the page
E)  into the pageF) All of the above
G) B) and D)

Question 15

In Ampere's law, the direction of the integration around the path:

Accepted Answer

A)  must be clockwise
B)  must be counterclockwise
C)  must be such as to follow the magnetic field lines
D)  must be along the wire in the direction of the current
E)  none of the aboveF) C) and E)
G) C) and D)

Question 16

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

Accepted Answer

A)  0
B)  1
C)  3
D)  5
E)  7F) D) and E)
G) C) and D) C

Question 17

A semi-infinite wire runs along the positive y axis, beginning at the origin (x = y = 0) and extending infinitely far in the +y direction.If the current in the wire is 12 A, what magnetic field does it create on the x axis at the point x = 3.5 cm?

Accepted Answer

A)  0 T
B)  3.4 x 10-5 T
C)  6.9 x 10-5 T
D)  1.4 x 10-4 T
E)  4.3 x 10-4 TF) A) and D)
G) C) and D)

Question 18

In Ampere's law, , the integration must be over any:

Accepted Answer

A)  surface
B)  closed surface
C)  path
D)  closed path
E)  closed path that surrounds all the current producingF) None of the above
G) C) and E)

Question 19

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

Accepted Answer

A)  north
B)  east
C)  south
D)  west
E)  zeroF) None of the above
G) B) and C)

Question 20

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

Accepted Answer

A)  1, 2, 3
B)  3, 2, 1
C)  1, 3, 2
D)  2, 3, 1
E)  2, 1, 3F) B) and C)
G) A) and D)

Exam 29: Magnetic Fields Due to Currents

A toroid with a square cross section carries current i.The magnetic field has its largest magnitude:

Correct Answer
verified

Two long parallel straight wires carry equal currents in opposite directions.At a point midway between the wires, the magnetic field they produce is:

Correct Answer
verified

The magnetic field outside a long straight current-carrying wire depends on the distance R from the wire axis according to:

Correct Answer
verified

Lines of the magnetic field produced by a long straight wire carrying a current are:

Correct Answer
verified

Suitable units for $\mu$ ₀ are:

Correct Answer
verified

The diagram shows three arrangements of circular loops, centered on vertical axes and carrying identical currents in the directions indicated.Rank the arrangements according to the magnitudes of the magnetic fields at the midpoints between the loops on the central axes, from least to greatest.

Correct Answer
verified

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

Correct Answer
verified

Correct Answer
verified

In an overhead straight wire, the current is north.The magnetic field due to this current, at our point of observation, is:

Correct Answer
verified

The magnetic field at any point in the xy plane is given by , where is the position vector of the point, A is a constant, and is a unit vector in the +z direction.The net current through a circle of radius R, in the xy plane and centered at the origin is given by:

Correct Answer
verified
D

Correct Answer
verified

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

Correct Answer
verified
E

Two long straight wires pierce the plane of the paper at vertices of an equilateral triangle as shown below.They each carry 2.0 A, out of the paper.The magnetic field at the third vertex (P) has magnitude:

Correct Answer
verified

In the figure, the current element , the point P, and the three vectors (1, 2, 3) are all in the plane of the page.The direction of , due to this current element, at the point P is:

Correct Answer
verified

In Ampere's law, the direction of the integration around the path:

Correct Answer
verified

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

Correct Answer
verified
C

A semi-infinite wire runs along the positive y axis, beginning at the origin (x = y = 0) and extending infinitely far in the +y direction.If the current in the wire is 12 A, what magnetic field does it create on the x axis at the point x = 3.5 cm?

Correct Answer
verified

In Ampere's law, , the integration must be over any:

Correct Answer
verified

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

Correct Answer
verified

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

Correct Answer
verified

Exam 29: Magnetic Fields Due to Currents

A toroid with a square cross section carries current i.The magnetic field has its largest magnitude:

Correct AnswerverifiedShow Answer

Two long parallel straight wires carry equal currents in opposite directions.At a point midway between the wires, the magnetic field they produce is:

Correct AnswerverifiedShow Answer

The magnetic field outside a long straight current-carrying wire depends on the distance R from the wire axis according to:

Correct AnswerverifiedShow Answer

Lines of the magnetic field produced by a long straight wire carrying a current are:

Correct AnswerverifiedShow Answer

Suitable units for μ\muμ 0 are:

Correct AnswerverifiedShow Answer

The diagram shows three arrangements of circular loops, centered on vertical axes and carrying identical currents in the directions indicated.Rank the arrangements according to the magnitudes of the magnetic fields at the midpoints between the loops on the central axes, from least to greatest.

Correct AnswerverifiedShow Answer

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

Correct AnswerverifiedShow Answer

The magnitude of the magnetic field at point P, at the center of the semicircle shown, is given by:

Correct AnswerverifiedShow Answer

In an overhead straight wire, the current is north.The magnetic field due to this current, at our point of observation, is:

Correct AnswerverifiedShow Answer

The magnetic field at any point in the xy plane is given by , where is the position vector of the point, A is a constant, and is a unit vector in the +z direction.The net current through a circle of radius R, in the xy plane and centered at the origin is given by:

Correct AnswerverifiedD

Correct AnswerverifiedShow Answer

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

Correct AnswerverifiedE

Two long straight wires pierce the plane of the paper at vertices of an equilateral triangle as shown below.They each carry 2.0 A, out of the paper.The magnetic field at the third vertex (P) has magnitude:

Correct AnswerverifiedShow Answer

In the figure, the current element , the point P, and the three vectors (1, 2, 3) are all in the plane of the page.The direction of , due to this current element, at the point P is:

Correct AnswerverifiedShow Answer

In Ampere's law, the direction of the integration around the path:

Correct AnswerverifiedShow Answer

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

Correct AnswerverifiedC

A semi-infinite wire runs along the positive y axis, beginning at the origin (x = y = 0) and extending infinitely far in the +y direction.If the current in the wire is 12 A, what magnetic field does it create on the x axis at the point x = 3.5 cm?

Correct AnswerverifiedShow Answer

In Ampere's law, , the integration must be over any:

Correct AnswerverifiedShow Answer

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

Correct AnswerverifiedShow Answer

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

Correct AnswerverifiedShow Answer

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Suitable units for $\mu$ ₀ are:

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified
D

Correct Answer
verified

Correct Answer
verified
E

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified
C

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified