Question 1

A coil is placed in a changing magnetic field and an emf is induced.What happens to the induced emf if the rate of change of magnetic field quadruples?

Accepted Answer

A)  There is no change. 
B)  The emf doubles. 
C)  The emf quadruples. 
D)  The emf increases by a factor of 16.

Question 2

A bar magnet is held above the center of a conducting ring in the horizontal plane.The magnet is dropped so it falls lengthwise toward the center of the ring.Will the falling magnet be attracted toward the ring or be repelled by the ring due to the magnetic interaction of the magnet and the ring?

Accepted Answer

A)  It will be attracted. 
B)  It will be repelled. 
C)  It will be attracted only if the north end of the magnet is the leading end as it falls toward the ring. 
D)  It will be attracted only if the south end of the magnet is the leading end as it falls toward the ring.

Question 3

A coil with a self-inductance of 0.80 mH experiences a constant current buildup from zero to 16 A in 0.50 s.What is the induced emf during this interval?

Accepted Answer

A)  0.0064 V 
B)  0.026 V 
C)  6.4 V 
D)  0.040 V 
E)  ​0.032 V

Question 4

The current in a coil with a self-inductance of 2.3 mH increases from 0 to 1.9 A in a tenth of a second.What is the induced emf in the coil?

Accepted Answer

A)  44 mV 
B)  4.4 mV 
C)  830 mV 
D)  0.012 V 
E)  ​87 mV

Question 5

A planar loop consisting of four turns of wire,each of which encloses 350 cm2,is oriented perpendicularly to a magnetic field that increases uniformly in magnitude from 19 mT to 35 mT in a time of 6.0 ms.What is the resulting induced current in the coil if the resistance of the coil is 6.0 Ω?

Accepted Answer

A)  16 mA 
B)  1560 mA 
C)  140 mA 
D)  62 mA 
E)  ​560 mA

Question 6

A straight wire of length 
Is oriented east-west and is in a magnetic field B pointing north.The wire is moving downward at a constant speed v.Which end of the rod is positively charged?

Accepted Answer

A)  neither 
B)  the east end 
C)  the west end 
D)  both ends

Question 7

A circuit consists of a 11.5-mH coil,a 9.0-V battery,a parallel combination of a 10-Ω resistor and a 6.0-Ω resistor,and a switch,all in series.What is the time constant of this circuit?

Accepted Answer

A)  7.2E-4 s 
B)  3.1E-3 s 
C)  1.2E-3 s 
D)  ​2.8E-2 s 
E)  ​This circuit has 2 time constants.

Question 8

Two loops of wire are arranged so that a changing current in one,the primary,will induce a current in the other,the secondary.The secondary loop has twice as many turns as the primary loop.As long as the current in the primary is steady at 3 A,the current in the secondary will be:

Accepted Answer

A)  3 A. 
B)  6 A. 
C)  1.5 A. 
D)  zero.

Question 9

In the United States,the value of ω for commercially generated power is ________ in SI units.

Accepted Answer

A)  50 
B)  60 
C)  120 
D)  377

Question 10

A sensitive ammeter is connected to a wire loop and placed within the magnetic field of a strong horseshoe magnet.The ammeter shows a deflection when:

Accepted Answer

A)  the wire is moved parallel to the field. 
B)  the wire is moved perpendicularly to the field. 
C)  neither wire nor magnet is moving. 
D)  the wire's axis is parallel to the field.

Question 11

Superconductors have been discussed as a means for electrical energy storage.Because they are resistanceless,a current once started in a loop would continue without loss.If a current of 1.0 × 104 A were started in a huge toroidal coil of radius 1.0 km and inductance 50 H,how much electrical energy (in kWh)could be stored?

Accepted Answer

A)  300 kWh 
B)  480 kWh 
C)  690 kWh 
D)  840 kWh

Question 12

A coil is placed in a magnetic field and has a flux ΦB through it.The coil is stressed so that its area reduces to 75% of its original value.If the plane of the coil stays the same and the flux through it remains the same,how must the magnetic field change?

Accepted Answer

A)  It must increase by 25%. 
B)  It must increase by 33%. 
C)  It must increase by 125%. 
D)  It must decrease by 25%.

Question 13

Two loops of wire are arranged so that a changing current in one will induce a current in the other.If the current in the first is increasing clockwise by 1.0 A every second,the induced current in the second loop will:

Accepted Answer

A)  be increasing counterclockwise. 
B)  stay constant. 
C)  increase clockwise also. 
D)  stay zero.

Question 14

A 0.200-m wire is moved parallel to a 0.500-T magnetic field at a speed of 1.50 m/s.What emf is induced across the ends of the wire?

Accepted Answer

A)  2.25 V 
B)  1.00 V 
C)  0.600 V 
D)  zero

Question 15

A uniform 1.0-T magnetic field passes through the plane of a wire loop 0.30 m2 in area.What flux passes through the loop when the direction of the 1.0-T field is at a 10° angle to the normal of the loop plane?

Accepted Answer

A)  3.3 T⋅m2 
B)  0.29 T⋅m2 
C)  0.30 T⋅m2 
D)  0.05 T⋅m2 
E)  ​0.30 T⋅m2

Question 16

The operation of a tape player to play music depends on which of the following?

Accepted Answer

A)  the Doppler effect 
B)  the photoelectric effect 
C)  the force acting on a current-carrying wire in a magnetic field 
D)  induced current from the motion of a magnet past a wire

Question 17

A 600-turn circular coil with an area of 0.0350 m2 is mounted on a rotating frame,which turns at a rate of 21.0 rad/s in the presence of a 0.0650-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 at a 75.0° angle to the field?

Accepted Answer

A)  zero 
B)  28.7 V 
C)  37.5 V 
D)  27.7 V 
E)  ​0.065 V

Question 18

One time constant after an RL circuit has its switch closed,how does the current I in it compare to the maximum current Imax that occurs for this circuit?

Accepted Answer

A)  I > Imax/2 
B)  I = Imax/2 
C)  I max/2 
D)  Without knowing R and L,this cannot be determined.

Question 19

A motor with a coil resistance of 12 Ω is attached to a voltage supply of 75 V.What is the current in the motor when it is running at its maximum speed with a back emf of 25 V?

Accepted Answer

A)  zero 
B)  4.2 A 
C)  8.3 A 
D)  6.3 A 
E)  ​600 A

Question 20

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 42.0°.What flux would go through the coil if the angle were changed to 29.0°?

Accepted Answer

A)  0.167 T·m2 
B)  0.135 T·m2 
C)  0.27 T·m2 
D)  0.231 T·m2 
E)  ​0.142 T·m2

Exam 20: Induced Voltages and Inductance

A coil is placed in a changing magnetic field and an emf is induced.What happens to the induced emf if the rate of change of magnetic field quadruples?

A bar magnet is held above the center of a conducting ring in the horizontal plane.The magnet is dropped so it falls lengthwise toward the center of the ring.Will the falling magnet be attracted toward the ring or be repelled by the ring due to the magnetic interaction of the magnet and the ring?

A coil with a self-inductance of 0.80 mH experiences a constant current buildup from zero to 16 A in 0.50 s.What is the induced emf during this interval?

The current in a coil with a self-inductance of 2.3 mH increases from 0 to 1.9 A in a tenth of a second.What is the induced emf in the coil?

A planar loop consisting of four turns of wire,each of which encloses 350 cm²,is oriented perpendicularly to a magnetic field that increases uniformly in magnitude from 19 mT to 35 mT in a time of 6.0 ms.What is the resulting induced current in the coil if the resistance of the coil is 6.0 Ω?

A straight wire of length Is oriented east-west and is in a magnetic field B pointing north.The wire is moving downward at a constant speed v.Which end of the rod is positively charged?

A circuit consists of a 11.5-mH coil,a 9.0-V battery,a parallel combination of a 10-Ω resistor and a 6.0-Ω resistor,and a switch,all in series.What is the time constant of this circuit?

Two loops of wire are arranged so that a changing current in one,the primary,will induce a current in the other,the secondary.The secondary loop has twice as many turns as the primary loop.As long as the current in the primary is steady at 3 A,the current in the secondary will be:

In the United States,the value of ω for commercially generated power is ________ in SI units.

A sensitive ammeter is connected to a wire loop and placed within the magnetic field of a strong horseshoe magnet.The ammeter shows a deflection when:

A coil is placed in a magnetic field and has a flux Φ_B through it.The coil is stressed so that its area reduces to 75% of its original value.If the plane of the coil stays the same and the flux through it remains the same,how must the magnetic field change?

Two loops of wire are arranged so that a changing current in one will induce a current in the other.If the current in the first is increasing clockwise by 1.0 A every second,the induced current in the second loop will:

A 0.200-m wire is moved parallel to a 0.500-T magnetic field at a speed of 1.50 m/s.What emf is induced across the ends of the wire?

A uniform 1.0-T magnetic field passes through the plane of a wire loop 0.30 m² in area.What flux passes through the loop when the direction of the 1.0-T field is at a 10° angle to the normal of the loop plane?

The operation of a tape player to play music depends on which of the following?

One time constant after an RL circuit has its switch closed,how does the current I in it compare to the maximum current I_max that occurs for this circuit?

A motor with a coil resistance of 12 Ω is attached to a voltage supply of 75 V.What is the current in the motor when it is running at its maximum speed with a back emf of 25 V?

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 42.0°.What flux would go through the coil if the angle were changed to 29.0°?