Deck 19: Electromagnetic Induction

Question 1

Two solenoids are close to each other,as shown in the figure,with the switch S open.When the switch is suddenly closed,which way will the induced current flow through the galvanometer in the left-hand solenoid?

A)from left to right
B)from right to left
C)There will be no induced current through the galvanometer.

Answer 1

B

Question 2

An outer metal ring surrounds an inner metal ring,as shown in the figure.The current in the outer ring is counterclockwise and decreasing.What is the direction of the induced current in the inner ring?

A)clockwise
B)counterclockwise
C)There is no induced current in the inner ring.

Answer 2

B

Question 3

A coil of wire containing N turns is in an external field that is perpendicular to the plane of the coil and it steadily changing in magnitude.Under these circumstances,an emf ε is induced in the coil.If the rate of change of the magnitude of the field and the number of turns in the coil are now doubled (but nothing else changes),what will be the induced emf in the coil?

A)2ε
B)ε/2
C)4ε
D)ε/4
E)ε

Answer 3

C

Question 4

A flat coil is in a uniform magnetic field.The magnetic flux through the coil is greatest when the plane of its area is

A)parallel to the magnetic field.
B)at 45° with the magnetic field.
C)perpendicular to the magnetic field.

Question 5

A coil lies flat on a tabletop in a region where the field vector points straight up.The magnetic field vanishes suddenly.When viewed from above,what is the sense of the induced current in this coil as the field fades?

A)The induced current flows counterclockwise.
B)The induced current flows clockwise.
C)There is no induced current in this coil.
D)The current flows clockwise initially, and then it flows counterclockwise before stopping.

Question 6

A coil lies flat on a horizontal tabletop in a region where the field points straight down.The magnetic field disappears suddenly.When viewed from above,what is the direction of the induced current in this coil as the field disappears?

A)counterclockwise
B)clockwise
C)clockwise initially, then counterclockwise before stopping
D)There is no induced current in this coil.

Question 7

A bar magnet is oriented above a copper ring,as shown in the figure.The magnet is dropped and passes completely through the ring.As viewed from above,what is the direction of the current induced in the ring after the magnet has completely passed through the ring and is somewhat below it?

A)There is no current in the ring.
B)counterclockwise
C)clockwise

Question 8

A circular coil lies flat on a horizontal surface.A bar magnet is held fixed above the center of the coil with its north pole pointing downward.What is the direction of the induced current in the coil,as viewed from above?

A)clockwise
B)counterclockwise
C)There is no current in the coil.

Question 9

A circular coil of copper wire is lying flat on a horizontal table.A bar magnet is held above the center of the coil with its south pole downward.The magnet and the coil are now both raised upward with the same velocities.As viewed from above,what is the direction of the current induced in the coil as the magnet approaches the coil?

A)counterclockwise
B)clockwise
C)No current is induced in the coil.
D)An emf but no current is induced in the coil.

Question 10

A circular coil of copper wire is lying flat on a horizontal table.A bar magnet is held above the center of the coil with its south pole downward.The magnet is released from rest and falls toward the coil.As viewed from above,what is the direction of the current induced in the coil as the magnet approaches the coil?

A)counterclockwise
B)clockwise
C)No current is induced in the coil.
D)An emf but no current is induced in the coil.

Question 11

A bar magnet is oriented above a copper ring,as shown in the figure.If the magnet is kept fixed while the ring is dropped,what is the direction of the current induced in the ring,as viewed from below the ring?

A)There is no current in the ring.
B)counterclockwise
C)clockwise

Question 12

According to Lenz's law,the induced current in a circuit always flows to oppose the external magnetic flux through the circuit.

Question 13

A bar magnet is oriented above a copper ring,as shown in the figure.If the magnet is pulled upward,what is the direction of the current induced in the ring,as viewed from above?

A)There is no current in the ring.
B)counterclockwise
C)clockwise

Question 14

A bar magnet is close to a solenoid,as shown in the figure.As viewed through the solenoid looking toward the magnet,what is the direction (clockwise or counterclockwise)of the current (if any)induced in the solenoid in each case?
(a)The magnet is pushed toward the solenoid.
(b)The magnet and solenoid both move to the right at 25 cm/s.

Question 15

According to Faraday's law,a coil in a strong magnetic field must have a greater induced emf in it than a coil in a weak magnetic field.

Question 16

A circular coil lies flat on a horizontal surface.A bar magnet is held above the center of the coil with its north pole pointing down.If the magnet is dropped from this position what is the direction of the induced current in the coil,as viewed from above?

A)counterclockwise
B)clockwise
C)An emf but no current is induced in the coil.
D)There is no current in the coil.

Question 17

At a certain instant,coil A is in a 10-T external magnetic field and coil B is in a 1-T external magnetic field.Both coils have the same area and are oriented at right angles to the field.Which coil will have a greater emf induced in it?

A)coil A
B)coil B
C)It is impossible to know without more information about the fields.

Question 18

A long straight wire lies on a horizontal table and carries an ever-increasing current toward the north.Two coils of wire lie flat on the table,one on either side of the wire.When viewed from above,the direction of the induced current in these coils is

A)clockwise in both coils.
B)counterclockwise in both coils.
C)clockwise in the east coil and counterclockwise in the west coil.
D)counterclockwise in the east coil and clockwise in the west coil.

Question 19

According to Lenz's law,the induced current in a circuit always flows to oppose the external magnetic field through the circuit.

Question 20

A coil lies flat on a level tabletop in a region where the field vector points straight up.The field suddenly grows stronger in magnitude.When viewed from above,what is the direction of the induced current in this coil as the field increases?

A)counterclockwise
B)clockwise
C)clockwise initially, then counterclockwise before stopping
D)There is no induced current in this coil.

Question 21

The wire in the figure carries a steady current I.What is true about the currents induced in each of the three loops shown? The wire and the three loops are all in the same plane.

A)No current is induced in any loop.
B)The currents are counterclockwise in all three loops.
C)The currents are clockwise in all three loops.
D)Loop A has clockwise current, loop B has no induced current, and loop C has counterclockwise current.
E)Loop A has counterclockwise current, loop B has no induced current, and loop C has clockwise current.

Question 22

As shown in the figure,a straight wire carries a steady current I.A metal bar is in contact with a pair of rails and is in upward motion with velocity of magnitude ν.The polarity of the induced emf in terminals X and Y is

A)X and Y are at the same potential.
B)X is positive and Y is negative.
C)Y is positive and X is negative.

Question 23

As shown in the figure,a metal bar is in contact with a pair of parallel rails.A steady,uniform,magnetic field B is present directed to the right.The bar is moving upward with velocity of magnitude ν.What is the polarity of the induced emf in terminals X and Y?

A)X and Y are at the same potential.
B)X is positive and Y is negative.
C)Y is positive and X is negative.

Question 24

The three loops of wire shown in the figure are all hanging in the same uniform magnetic field that is perpendicular to the page and does not vary with time.Loop 1 swings back and forth like the bob in a pendulum,Loop 2 rotates about a vertical axis,and Loop 3 oscillates up and down at the end of a spring.Which loop (or loops)will have an emf induced in them?

A)Loop 1
B)Loop 2
C)Loop 3
D)Loops 1 and 3
E)Loops 2 and 3

Question 25

As shown in the figure,a C-shaped conductor is in a uniform magnetic field B out of the page,and the magnitude of B is increasing.What is the polarity of the induced emf in terminals X and Y?

A)X and Y are at the same potential.
B)X is positive and Y is negative.
C)Y is positive and X is negative.

Question 26

As shown in the figure,two solenoids are side by side.The switch S is initially open.When S is suddenly closed,the direction of the induced current through the resistor R is

A)from a to b.
B)from b to a.
C)No current is induced.

Question 27

As shown in the figure,two parallel wires carry a current I in opposite directions,and this current is decreasing.A rectangular loop is centered between the wires.The direction of the induced current through the resistor R is

A)from a to b.
B)from b to a.
C)No current is induced.

Question 28

As shown in the figure,a coil of wire is placed in the xy-plane,centered on the z-axis.A solenoid is centered on the z-axis and is carrying a steady dc current.Which one of the following actions will not result induce an emf in the coil?

A)Rotate the coil about the x-axis.
B)Rotate the coil about the y-axis.
C)Rotate the coil about the z-axis.
D)Move the coil toward point P.
E)Change the current in the solenoid.

Question 29

A circular wire ring is situated above a long straight wire,as shown in the figure.The straight wire has a current I flowing to the right,and this current is increasing at a constant rate.Which of the following statements is true?

A)There is an induced current in the wire ring, directed in clockwise orientation.
B)There is an induced current in the wire ring, directed in a counterclockwise orientation.
C)There is no induced current in the wire ring.

Question 30

As shown in the figure,one end of a metal bar is in contact with a circular rail and the other end is pivoted at P.A steady uniform,magnetic field B into the page is present.As the bar rotates about point P in a clockwise direction,the direction of the induced current through the resistor R is

A)from a to b.
B)from b to a.
C)No current is induced.

Question 31

The wire in the figure carries a current I that is decreasing with time at a constant rate.The wire and the three loops are all in the same plane.What is true about the currents induced in each of the three loops shown?

A)No current is induced in any loop.
B)The currents are counterclockwise in all three loops.
C)The currents are clockwise in all three loops.
D)Loop A has clockwise current, loop B has no induced current, and loop C has counterclockwise current.
E)Loop A has counterclockwise current, loop B has no induced current, and loop C has clockwise current.

Question 32

As shown in the figure,a straight wire carries a current I into the page.The wire passes through the center of a toroidal coil.If the current I is quickly reduced to zero,the direction of the induced current through the resistor R is

A)from a to b.
B)from b to a.
C)No current is induced.

Question 33

A transformer is a device used to

A)transform an alternating current into a direct current.
B)transform a direct current into an alternating current.
C)increase or decrease an ac voltage.
D)increase or decrease a dc voltage.

Question 34

In the figure,a bar magnet moves away from the solenoid.The direction of the induced current through the resistor R is

A)from a to b.
B)from b to a.
C)No current is induced.

Question 35

The wire in the figure carries a current I that is increasing with time at a constant rate.The wire and the three loops are all in the same plane.What is true about the currents induced in each of the three loops shown?

A)No current is induced in any loop.
B)The currents are counterclockwise in all three loops.
C)The currents are clockwise in all three loops.
D)Loop A has clockwise current, loop B has no induced current, and loop C has counterclockwise current.
E)Loop A has counterclockwise current, loop B has no induced current, and loop C has clockwise current.

Question 36

As shown in the figure,two solenoids are in line.The switch S,initially closed,is suddenly opened.Just after opening S,what is the polarity of the induced emf in terminals X and Y?

A)X and Y are at the same potential.
B)X is positive and Y is negative.
C)Y is positive and X is negative.

Question 37

As shown in the figure,a metal bar is in contact with a pair of parallel rails and is in motion with an upward velocity of magnitude ν.A uniform magnetic field is present, field vector directed downward as shown.The direction of the induced current through the resistor R is

A)from a to b.
B)from b to a.
C)No current is induced.

Question 38

As shown in the figure,a battery supplies a steady current to the solenoid on the left.The two solenoids are moving toward each other with speeds v.The direction of the induced current through the resistor R is

A)from a to b.
B)from b to a.
C)No current is induced.

Question 39

As shown in the figure,a metal bar is in contact with a pair of metal parallel rails.A steady uniform magnetic field B,perpendicular to the plane of the rails and pointing outward from the page,is present.The bar is in downward motion with velocity of magnitude ν.The direction of the induced current through the resistor R is

A)from a to b.
B)from b to a.
C)No current is induced.

Question 40

An ac generator consisting of a coil with N turns rotating at angular speed ω in an external magnetic field B produces a maximum emf ε₀.If you now decrease the number of turns in the coil to N/2 and at the same time cause it to rotate twice as fast,what will be the new maximum emf if you do not change any of the other quantities?

A)4ε₀
B)2ε₀
C)ε₀
D)ε₀/2
E)ε₀/4

Question 41

If the primary coil of a transformer contains more loops than the secondary coil then it is a

A)step-up transformer.
B)step-down transformer.

Question 42

A rectangular loop of wire that can rotate about an axis through its center is placed between the poles of a magnet in a field of 0.40 T,as shown in the figure.The length of the loop L is 0.16 m and its width w is 0.040 m.What is the magnetic flux through the loop when the plane of the loop is parallel to the field?

A)13 × 10^-3 T ∙ m²
B)2.6 × 10³ T ∙ m²
C)0.80 T ∙ m²
D)2.6 × 10^-3 T ∙ m²
E)0 T ∙ m²

Question 43

A flat circular coil having 16 turns,each of diameter 20 cm,is in a uniform and steady 0.13-T B field.
(a)Find the total magnetic flux through the coil when the field is perpendicular to the plane of the coil.
(b)If the coil is rotated in 10 ms so its plane is parallel to the field vector,find the average induced emf in the coil.

Question 44

A closed flat loop conductor with radius is located in a changing uniform magnetic field.If the emf induced in the loop is what is the rate at which the magnitude of the field is changing if the field vector is oriented perpendicular to the plane in which the loop lies?

A)0.16 T/s
B)1.0 T/s
C)0.080 T/s
D)2.0 T/s

Question 45

A rectangular loop of wire that can rotate about an axis through its center is placed between the poles of a magnet in a field of 0.40 T,as shown in the figure.The length of the loop L is 0.16 m and its width w is 0.040 m.What is the magnetic flux through the loop when the plane of the loop is perpendicular to the field?

A)13 × 10^-3 T ∙ m²
B)2.6 × 10³ T ∙ m²
C)0.80 T ∙ m²
D)2.6 × 10^-3 T ∙ m²
E)0 T ∙ m²

Question 46

A conductor is formed into a flat loop that encloses an area of The plane of the loop is oriented at a 30.0° angle with the xy-plane.A uniform time-varying field is oriented parallel to the z-axis.If the emf induced in the loop is what is the rate at which the magnitude of the field strength is changing?

A)29 T/s
B)22 T/s
C)50 T/s
D)13 T/s

Question 47

A flat circular loop of radius 0.10 m is rotating in a uniform field of 0.20 T.Find the magnetic flux through the loop when the plane of the loop and the field vector are perpendicular.

A)0 T ∙ m²
B)3.1 × 10^-3 T ∙ m²
C)5.5 × 10^-3 T ∙ m²
D)6.3 × 10^-3 T ∙ m²

Question 48

A flat circular loop of radius 0.10 m is rotating in a uniform field of 0.20 T.Find the magnetic flux through the loop when the plane of the loop and the field vector are parallel.

A)0 T ∙ m²
B)3.1 × 10^-3 T ∙ m²
C)5.5 × 10^-3 T ∙ m²
D)6.3 × 10^-3 T ∙ m²

Question 49

As shown in the figure,a large round loop of 269 turns and radius 67.0 cm carries a current of I = A small square loop of 31.0 turns and 1.00 cm on a side is placed at the center of the large loop.If the current in the large loop drops to 0.00 A in 0.0470 s,find the induced emf in the small loop.The square loop is small enough that you can assume that the field in its region is uniform and equal to the field at the center of the round loop.(μ₀ = 4π × 10^-7 T ∙ m/A)

Question 50

A circular conducting loop with a radius of and a small gap filled with a resistor is oriented in the If a uniform field of making an angle of with the increases to in what is the magnitude of the current that will be induced in the loop if it has negligible resistance?

A)0.01530393 A
B)0.08835729 A
C)0.15303932 A
D)0 A

Question 51

A transformer is a device that normally

A)operates on either dc or ac.
B)operates only on ac.
C)operates only on dc.

Question 52

If the secondary coil of a transformer contains more loops than the primary coil,then it is a

A)step-up transformer.
B)step-down transformer.

Question 53

A rectangular loop of wire that can rotate about an axis through its center is placed between the poles of a magnet in a field of 0.40 T,as shown in the figure.The length of the loop L is 0.16 m and its width w is 0.040 m.What is the magnetic flux through the loop when the plane of the loop makes an angle of 60° with the field?

A)2.6 × 10^-3 T ∙ m²
B)1.3 × 10^-3 T ∙ m²
C)0 T ∙ m²
D)2.2 × 10^-3 T ∙ m²
E)0.80 T ∙ m²

Question 54

A flux of 4.0 × 10^-5 T ∙ m² is maintained through a coil of area 7.5 cm² for 0.50 s.What emf is induced in this coil during this time by this flux?

A)8.0 × 10^-5 V
B)4.0 × 10^-5 V
C)3.0 × 10^-5 V
D)2.0 × 10^-5 V
E)No emf is induced in this coil.

Question 55

A flat coil having 40 turns,each one of cross-sectional area 12.0 cm²,is oriented with its plane perpendicular to a uniform field.The field varies steadily from 0.00 T to 1.20 T in 20.0 ms.What emf is induced in the coil during this time?

Question 56

As shown in the figure,a uniform magnetic field B is confined to a cylindrical volume of radius 0.050 m.This field is directed into the plane of the page and its magnitude is increasing at a constant rate of Calculate the magnitude and direction (clockwise or counterclockwise)of the current induced in a circular wire ring of radius 0.16 m and resistance that encircles the magnetic field region.

Question 57

A flat circular loop of radius 0.10 m is rotating in a uniform field of 0.20 T.Find the magnetic flux through the loop when the plane of the loop and the field vector are at an angle of 30°.

A)0 T ∙ m²
B)3.1 × 10^-3 T ∙ m²
C)5.5 × 10^-3 T ∙ m²
D)6.3 × 10^-3 T ∙ m²

Question 58

A 2.00-m long metal wire is formed into a square and placed in the horizontal xy-plane.A uniform field is oriented at 30° above the horizontal with a magnitude of 0.344 T.What is the magnetic flux through the square due to this field?

A)0.0745 T ∙ m²
B)0.172 T ∙ m²
C)0.0430 T ∙ m²
D)0.298 T ∙ m²

Question 59

A bar magnet is pushed through a coil of wire of cross-sectional area 0.020 m² as shown in the figure.The coil has seven turns,and the rate of change of the magnitude of the field in it due to the motion of the bar magnet is 0.040 T/s.What is the magnitude of the induced emf in that coil of wire?

A)5.6 × 10^-3 V
B)5.6 × 10^-2 V
C)5.6 × 10^-1 V
D)5.6 × 10^-4 V
E)5.6 × 10^-5 V

Question 60

A flat circular loop having one turn and radius 5.0 cm is positioned with its plane perpendicular to a uniform 0.60-T field.The area of the loop is suddenly reduced to essentially zero in 0.50 ms.What emf is induced in the loop?

Question 61

A flat coil is wrapped with 200 turns of very thin wire on a square frame with sides 18 cm long.A uniform magnetic field is applied perpendicular to the plane of the coil.If the magnitude of the field changes uniformly from 0.50 T to 0.00 T in 8.0 s,find the emf induced in the coil.

A)2.1 mV
B)4.1 mV
C)0.21 V
D)0.41 V

Question 62

A flat square coil of wire with 15 turns and an area of 0.40 m² is placed with the plane of its area parallel to a 0.75-T field.The coil is flipped so its plane is perpendicular to the field in a time of 0.050 s.What is the magnitude of the average induced emf in the coil?

A)6.0 V
B)36 V
C)45 V
D)90 V

Question 63

A flat rectangular coil with dimensions of 8.0 cm × 10 cm is dropped from a zero magnetic field position into a 1.4-T field in 0.10 s.The coil has 60 turns and is perpendicular to the field.What is the average induced emf in the coil as a result of this action?

A)8.6 V
B)2.4 V
C)6.7 V
D)3.6 V
E)0 V

Question 64

A airplane having a metal surface and a wingspan of 25.0 m flies horizontally at 200 m/s where the earth's field is vertical with magnitude 45.0 μT.
(a)What emf is induced across the wings?
(b)What wingspan would the plane need to produce 1.00-V emf across its wings?
(c)The plane now reverses direction.Does the polarity of the wingtip emf change? That is,if the left wing was positive before,does it now become negative?

Question 65

A flat coil having 160 turns,each with an area of 0.20 m²,is placed with the plane of its area perpendicular to a 0.40T field.The magnitude of the field changes uniformly from 0.40 T in the +x direction to 0.40 T in the -x direction in 2.0 s.If the resistance of the coil is 16 Ω,at what rate is power generated in the coil during this change?

A)5.0 W
B)10 W
C)15 W
D)20 W

Question 66

A constant uniform magnetic field of 0.50 T is applied at right angles to the plane of a flat rectangular loop of area 3.0 × If the area of this loop changes steadily from its original value to a new value of 1.6 × 10^-3 m² in 1.6 s,what is the emf induced in the loop?

A)1.6 × V
B)0 V
C)7.5 × V
D)4.4 × V
E)9.0 × V

Question 67

A conducting rod of length ℓ= 25 cm is placed on a U-shaped metal wire that is connected to a lightbulb having a resistance of 8.0 Ω,as shown in the figure.The wire and the rod are in the plane of the page.A constant uniform field of 0.40 T in magnitude is applied perpendicular to and into the paper.An applied external force pulls the rod to the right with a constant speed of 6.0 m/s.What is the magnitude of the emf induced in the rod?

A)0.20 V
B)0.30 V
C)0.40 V
D)0.50 V
E)0.60 V

Question 68

The area of a rectangular loop of wire is 3.6 × The loop is placed in a uniform field that changes steadily from 0.20 T to 1.4 T in 1.6 s.The plane of the loop is perpendicular to the direction of the field.What is the magnitude of the induced emf in that loop?

A)2.8 × V
B)2.7 × V
C)0 V
D)1.8 × V
E)3.0 × V

Question 69

As shown in the figure,a region of space contains a uniform field of magnitude 2.8 T,directed straight into the plane of the page in the region shown.Outside this region the magnetic field is zero.A rectangular loop measuring 0.20 m by 0.60 m and having a resistance of 2 Ω is being pulled into the magnetic field by an external force,as shown.
(a)What is the direction (clockwise or counterclockwise)of the current induced in the loop?
(b)Calculate the magnitude of the external force F_ext that is required to move the loop at a constant speed of 3.9 m/s.

Question 70

An electromagnetic flowmeter is useful when it is desirable not to interrupt the system in which the fluid is flowing (such as the blood in an artery during heart surgery).Such a device is illustrated in the figure.The conducting fluid moves with speed v in a tube of diameter d.Perpendicular to this tube is a magnetic field B.A voltage V is induced between opposite sides of the tube due to the motion of the conducting fluid in the magnetic field.For a certain case,B = 0.120 T,d = 1.2 cm,and the measured voltage is Determine the speed of the fluid.

A)2.0 m/s
B)11 m/s
C)0.075 m/s
D)1.1 m/s
E)750 m/s

Question 71

The magnetic flux through a coil changes steadily from 4.0 × 10^-5 T ∙ m² to 5.0 × 10^-5 T ∙ m² in 0.10 s.What emf is induced in this coil?

A)5.0 × 10^-4 V
B)4.0 × 10^-4 V
C)1.0 × 10^-4 V
D)None of the given answers are correct.

Question 72

An eagle,with a wingspread of 2.0 m,flies toward the north at 8.0 m/s in a region where the vertical component of the earth's field is 0.20 × 10^-4 T.What emf would be developed between the eagle's wing tips? (It has been speculated that this phenomenon could play a role in the navigation of birds,but the effect is too small,in all likelihood.)

Question 73

It is known that birds can detect the earth's magnetic field,but the mechanism of how they do this is not known.It has been suggested that perhaps they detect a motional emf as they fly north to south,but it turns out that the induced voltages are small compared to the voltages normally encountered in cells,so this is probably not the mechanism involved.To check this out,calculate the induced voltage across the wingtips of a wild goose with a wingspan of if it is flying directly south at at a point where the earth's field is 5.0 ×10^-5 T directed downward from the horizontal by

A)0.50 mV
B)0.60 mV
C)0.78 mV
D)0.060 mV
E)0.25 mV

Question 74

A round flat metal coil has 180 turns and negligible resistance.It is connected in a series circuit with a resistor,with nothing else in the circuit.You measure that a current flows through the resistor when a magnetic field through the coil,perpendicular to its area,is changing at What is the radius of the coil?

A)0.25 m
B)0.014 m
C)0.54 m
D)0.043 m

Question 75

A single-turn loop of wire,having a resistance of 8.00 Ω and a cross-sectional area 200 cm²,is perpendicular to a uniform field that increases in magnitude steadily from 0.200 T to 2.800 T in 2.20 seconds.What is the magnitude of the induced current in the loop?

A)2.95 A
B)3.18 A
C)0 A
D)3.18 mA
E)2.95 mA

Question 76

A long vertical wire carries a steady 70 A current.As shown in the figure,a pair of horizontal rails are 0.20 m apart.A 20-Ω resistor connects points a and b,at the end of the rails.A bar is in contact with the rails,and is moved by an external force with a constant horizontal velocity of 0.90 m/s to the right,as shown.The bar and the rails have negligible resistance.At the instant that the bar is 0.20 m from the wire,what are the induced current in the resistor and its direction through the resistor? (μ₀ = 4π × 10^-7 T ∙ m/A)

A)0.63 μA, from a to b
B)0.63 μA, from b to a
C)0.32 μA, from a to b
D)0.32 μA, from b to a
E)1.9 μA, from b to a

Question 77

As shown in the figure,a wire and a 10-Ω resistor are used to form a circuit in the shape of a square with dimensions 20 cm by 20 cm.A uniform but non-steady field is directed into the plane of the circuit.The magnitude of the field is steadily decreased from 2.70 T to 0.90 T in a time interval of 96 ms.What is the induced current in the circuit,and what is its direction through the resistor?

A)75 mA, from b to a
B)45 mA, from b to a
C)75 mA, from a to b
D)45 mA, from a to b
E)110 mA, from a to b

Question 78

A conducting rod with a length ℓ = 25 cm is placed on a U-shaped metal wire that is connected to a lightbulb having a resistance of 8.0 Ω as shown in the figure.The wire and the rod are in the plane of the page.A constant uniform field of 0.40 T in magnitude is applied perpendicular to and into the paper.An external applied force moves the rod to the right with a constant speed of 6.0 m/s.What are the magnitude and direction of the induced current in the circuit?

A)17 mA clockwise
B)17 mA counterclockwise
C)75 mA counterclockwise
D)75 mA clockwise
E)52 mA clockwise

Question 79

A round flat conducting loop is placed perpendicular to a uniform 0.50 T field.If the area of the loop increases at a rate of 3.0 × /s,what is the induced emf in the loop?

A)4.3 mV
B)0 mV
C)1.5 mV
D)1.7 mV
E)5.5 mV

Question 80

A circular coil of 20 turns and radius 5.0 cm is placed with its plane oriented at 90° to a uniform field of The field is now increased at a steady rate,reaching a value of after 4.0 seconds.What emf is induced in the coil?

A)0.016 V
B)0.021 V
C)0.026 V
D)0.031 V
E)0.036 V