Question 1

By what factor is the self-inductance of an air solenoid changed if its length and number of coil turns are both multiplied by seven?

Accepted Answer

A) 1/7 
B) 7 
C) 1 
D) 49 
E) 1/49 
A) 1/7 
B) 7 
C) 1 
D) 49 
E) 1/49 B

Question 2

A coil in a magnetic field encloses a flux of 0.196 T·m2 when the angle between the normal to the coil and the direction of the magnetic field is 62.0°.What flux would go through the coil if the angle were changed to 38.9°?

Accepted Answer

A) 0.118 T·m2 
B) 0.123 T·m2 
C) 0.539 T·m2 
D) 0.325 T·m2 
E) 0.139 T·m2 
A) 0.118 T·m2 
B) 0.123 T·m2 
C) 0.539 T·m2 
D) 0.325 T·m2 
E) 0.139 T·m2 D

Question 3

A loop of area 0.384 m2 is in a uniform 0.0565-T magnetic field.If the flux through the loop is 6.10 × 10-3 T·m2,what angle does the normal to the plane of the loop make with the direction of the magnetic field?

Accepted Answer

A) 73.7° 
B) 89.3° 
C) 16.3° 
D) 76.0º 
E) This is not possible. 
A) 73.7° 
B) 89.3° 
C) 16.3° 
D) 76.0º 
E) This is not possible. A

Question 4

A motor with a coil resistance of 12.4 Ω is attached to a voltage supply of 66.4 V.What is the current in the motor when it is running at its maximum speed with a back emf of 22.6 V?

Accepted Answer

A) zero 
B) 3.53 A 
C) 7.18 A 
D) 5.35 A 
E) 543 A 
A) zero 
B) 3.53 A 
C) 7.18 A 
D) 5.35 A 
E) 543 A

Question 5

A double loop of wire (making 2 turns)is in the x-y plane centered at the origin.A uniform magnetic field is increasing at a constant rate in the positive z-direction.Viewed from the positive z-axis,in which direction is the induced magnetic field in the loop?

Accepted Answer

A) in the positive z-direction 
B) in the negative z-direction 
C) There is no induced field because of the double loop. 
D) There is no induced field because the rate of change of the magnetic field is constant. 
A) in the positive z-direction 
B) in the negative z-direction 
C) There is no induced field because of the double loop. 
D) There is no induced field because the rate of change of the magnetic field is constant.

Question 6

A changing current in one loop of wire can induce a current in another loop of wire even though the wires do not touch.The induced current appears almost instantaneously for loops close together.How can this energy exchange happen?

Accepted Answer

A) This is one of those things for which science has no adequate explanation yet. 
B) The second loop is affected by the thermal exchange from the heating of the first loop. 
C) It is a gravitational effect on the electrons. 
D) It is done via an electromagnetic wave. 
A) This is one of those things for which science has no adequate explanation yet. 
B) The second loop is affected by the thermal exchange from the heating of the first loop. 
C) It is a gravitational effect on the electrons. 
D) It is done via an electromagnetic wave.

Question 7

The unit of inductance,the henry,is equivalent to

Accepted Answer

A) V·s/A. 
B) V/m. 
C) J/C. 
D) none of the units given. 
A) V·s/A. 
B) V/m. 
C) J/C. 
D) none of the units given.

Question 8

"GFI" stands for:

Accepted Answer

A) grand flux indicator. 
B) ground forcing indicator. 
C) ground fault interrupter. 
D) gauss-free invention. 
A) grand flux indicator. 
B) ground forcing indicator. 
C) ground fault interrupter. 
D) gauss-free invention.

Question 9

The self-inductance of a solenoid increases under which of the following conditions?

Accepted Answer

A) Only the solenoid length is increased. 
B) Only the cross sectional area is decreased. 
C) Only the number of coils per unit length is decreased. 
D) Only the number of coils is increased. 
A) Only the solenoid length is increased. 
B) Only the cross sectional area is decreased. 
C) Only the number of coils per unit length is decreased. 
D) Only the number of coils is increased.

Question 10

The "back emf" of a motor refers to a source of voltage that

Accepted Answer

A) occurs when the motor runs backwards. 
B) occurs when the motor is used as a generator. 
C) is biggest when the current through the motor is biggest. 
D) is biggest when the motor turns fastest. 
A) occurs when the motor runs backwards. 
B) occurs when the motor is used as a generator. 
C) is biggest when the current through the motor is biggest. 
D) is biggest when the motor turns fastest.

Question 11

A bar magnet is falling through a loop of wire with constant velocity.The south pole enters first.As the magnet leaves the wire,the induced current (as viewed from above):

Accepted Answer

A) is clockwise. 
B) is counterclockwise. 
C) is zero. 
D) is along the length of the magnet. 
A) is clockwise. 
B) is counterclockwise. 
C) is zero. 
D) is along the length of the magnet.

Question 12

A 460-turn solenoid of length 30.0 cm and radius 4.00 cm carries a current of 3.50 A. What is the magnetic field strength inside the coil at its midpoint?
-What is the magnetic flux through a circular cross-sectional area of the solenoid at its midpoint?

Accepted Answer

A) ​1.02E-5 T/m2 
B) ​3.05E-6 T/m2 
C) ​2.49E-7 T/m2 
D) ​3.39E-5 T/m2 
A) ​1.02E-5 T/m2 
B) ​3.05E-6 T/m2 
C) ​2.49E-7 T/m2 
D) ​3.39E-5 T/m2

Question 13

A uniform 1.72-T magnetic field passes through the plane of a wire loop 0.46 m2 in area.What flux passes through the loop when the direction of the 1.72-T field is at a 38.4° angle to the normal of the loop plane?

Accepted Answer

A) 2.9 T⋅m2 
B) 0.49 T⋅m2 
C) 0.62 T⋅m2 
D) 0.63 T⋅m2 
E) 0.79 T⋅m2 
A) 2.9 T⋅m2 
B) 0.49 T⋅m2 
C) 0.62 T⋅m2 
D) 0.63 T⋅m2 
E) 0.79 T⋅m2

Question 14

A 420-turn circular coil with an area of 0.0650 m2 is mounted on a rotating frame,which turns at a rate of 22.3 rad/s in the presence of a 0.0550-T uniform magnetic field that is perpendicular to the axis of rotation.What is the instantaneous emf in the coil at the moment that the normal to its plane is perpendicular to the field?

Accepted Answer

A) 33.5 V 
B) zero 
C) 0.0673 V 
D) 747 V 
E) 1.50 V 
A) 33.5 V 
B) zero 
C) 0.0673 V 
D) 747 V 
E) 1.50 V

Question 15

A coil with a self-inductance of 0.90 mH experiences a constant current buildup from zero to 15 A in 0.65 s.What is the induced emf during this interval?

Accepted Answer

A) 8.78E-3 V 
B) 2.08E-2 V 
C) 8.78E+2 V 
D) 2.56E-2 V 
E) 2.31E-2 V 
A) 8.78E-3 V 
B) 2.08E-2 V 
C) 8.78E+2 V 
D) 2.56E-2 V 
E) 2.31E-2 V

Question 16

An air-core inductor has 920 turns/m and an internal volume of 3.0 cm3.What is its inductance?

Accepted Answer

A) 3.2 μH 
B) 2.8 mH 
C) 0.35 H 
D) 32 μH 
E) Insufficient information is given. 
A) 3.2 μH 
B) 2.8 mH 
C) 0.35 H 
D) 32 μH 
E) Insufficient information is given.

Question 17

An RL circuit has L = 0.45 H and R = 3.5 Ω.It is connected to a battery with ε = 25 V at time t = 0.Find the energy stored in the inductor when the current in the circuit is 0.25 A.

Accepted Answer

A) 14 mJ 
B) 28 J 
C) 110 J 
D) 3.2 mJ 
E) 800 J 
A) 14 mJ 
B) 28 J 
C) 110 J 
D) 3.2 mJ 
E) 800 J

Question 18

A circular loop is suspended in a uniform magnetic field as shown in the figure.  
​
If the loop area increases,what affect does this have on the induced current?

Accepted Answer

A) The induced current is clockwise. 
B) The induced current is counterclockwise. 
C) There is no induced current. 
D) We would need to know the magnitude of the magnetic field. 
A) The induced current is clockwise. 
B) The induced current is counterclockwise. 
C) There is no induced current. 
D) We would need to know the magnitude of the magnetic field.

Question 19

An electric motor draws a current of 2.60 A from a 18.0-V battery when it runs at normal speed.If the motor's armature is "jammed" so that it cannot rotate,the current suddenly rises to 10.0 A.What is the back emf of the motor when running at normal speed?

Accepted Answer

A) 4.68 V 
B) 10.0 V 
C) 22.7 V 
D) 13.3 V 
E) 133 V 
A) 4.68 V 
B) 10.0 V 
C) 22.7 V 
D) 13.3 V 
E) 133 V

Question 20

A circuit consists of a 11.4-mH coil,a 19-Ω resistor,a 5.0-Ω resistor,a 10-V battery and a switch,all in series.What is the time constant of this circuit?

Accepted Answer

A) 2.1E-3 s 
B) 4.8E-3 s 
C) 2.9E-3 s 
D) 4.8E-4 s 
E) 4.2E-1 s 
A) 2.1E-3 s 
B) 4.8E-3 s 
C) 2.9E-3 s 
D) 4.8E-4 s 
E) 4.2E-1 s

Exam 20: Induced Voltages and Inductance

By what factor is the self-inductance of an air solenoid changed if its length and number of coil turns are both multiplied by seven?

A coil in a magnetic field encloses a flux of 0.196 T·m2 when the angle between the normal to the coil and the direction of the magnetic field is 62.0°.What flux would go through the coil if the angle were changed to 38.9°?

A loop of area 0.384 m2 is in a uniform 0.0565-T magnetic field.If the flux through the loop is 6.10 × 10-3 T·m2,what angle does the normal to the plane of the loop make with the direction of the magnetic field?

A motor with a coil resistance of 12.4 Ω is attached to a voltage supply of 66.4 V.What is the current in the motor when it is running at its maximum speed with a back emf of 22.6 V?

A double loop of wire (making 2 turns)is in the x-y plane centered at the origin.A uniform magnetic field is increasing at a constant rate in the positive z-direction.Viewed from the positive z-axis,in which direction is the induced magnetic field in the loop?

A changing current in one loop of wire can induce a current in another loop of wire even though the wires do not touch.The induced current appears almost instantaneously for loops close together.How can this energy exchange happen?

The unit of inductance,the henry,is equivalent to

"GFI" stands for:

The self-inductance of a solenoid increases under which of the following conditions?

The "back emf" of a motor refers to a source of voltage that

A bar magnet is falling through a loop of wire with constant velocity.The south pole enters first.As the magnet leaves the wire,the induced current (as viewed from above):

A 460-turn solenoid of length 30.0 cm and radius 4.00 cm carries a current of 3.50 A. What is the magnetic field strength inside the coil at its midpoint? -What is the magnetic flux through a circular cross-sectional area of the solenoid at its midpoint?

A uniform 1.72-T magnetic field passes through the plane of a wire loop 0.46 m2 in area.What flux passes through the loop when the direction of the 1.72-T field is at a 38.4° angle to the normal of the loop plane?

A coil with a self-inductance of 0.90 mH experiences a constant current buildup from zero to 15 A in 0.65 s.What is the induced emf during this interval?

An air-core inductor has 920 turns/m and an internal volume of 3.0 cm3.What is its inductance?

An RL circuit has L = 0.45 H and R = 3.5 Ω.It is connected to a battery with ε = 25 V at time t = 0.Find the energy stored in the inductor when the current in the circuit is 0.25 A.

A circular loop is suspended in a uniform magnetic field as shown in the figure. ​ If the loop area increases,what affect does this have on the induced current?

An electric motor draws a current of 2.60 A from a 18.0-V battery when it runs at normal speed.If the motor's armature is "jammed" so that it cannot rotate,the current suddenly rises to 10.0 A.What is the back emf of the motor when running at normal speed?

A circuit consists of a 11.4-mH coil,a 19-Ω resistor,a 5.0-Ω resistor,a 10-V battery and a switch,all in series.What is the time constant of this circuit?

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A coil in a magnetic field encloses a flux of 0.196 T·m² when the angle between the normal to the coil and the direction of the magnetic field is 62.0°.What flux would go through the coil if the angle were changed to 38.9°?

A loop of area 0.384 m² is in a uniform 0.0565-T magnetic field.If the flux through the loop is 6.10 × 10-³ T·m²,what angle does the normal to the plane of the loop make with the direction of the magnetic field?

A uniform 1.72-T magnetic field passes through the plane of a wire loop 0.46 m² in area.What flux passes through the loop when the direction of the 1.72-T field is at a 38.4° angle to the normal of the loop plane?

An air-core inductor has 920 turns/m and an internal volume of 3.0 cm³.What is its inductance?

A circular loop is suspended in a uniform magnetic field as shown in the figure. If the loop area increases,what affect does this have on the induced current?