Question 1

An ideal solenoid has a length of 25 mm.If the windings are compressed so that the length is reduced to 1/2 of its original length how does the inductance change?

Accepted Answer

A)  1/4 of original 
B)  to 1/2 of original 
C)  twice the original 
D)  quadruple the original 
A)  1/4 of original 
B)  to 1/2 of original 
C)  twice the original 
D)  quadruple the original

Question 2

A series LR circuit includes a 9.0.V battery,a resistance of 0.500 $\Omega$,and an inductance of 0.800 H.What is the greatest energy stored by the inductor after the switch is closed?

Accepted Answer

A)  33.0 mJ 
B)  13.0 mJ 
C)  130 J 
D)  65.0 J 
E)  33.0 J 
A)  33.0 mJ 
B)  13.0 mJ 
C)  130 J 
D)  65.0 J 
E)  33.0 J

Question 3

The back emf of an electric motor is greatest

Accepted Answer

A)  when the motor is just starting up. 
B)  when the motor is halfway to operating speed. 
C)  when the motor is at 71% of the operating speed. 
D)  when the motor is at full operating speed. 
E)  at all times since it is a constant when the motor is running at any speed. 
A)  when the motor is just starting up. 
B)  when the motor is halfway to operating speed. 
C)  when the motor is at 71% of the operating speed. 
D)  when the motor is at full operating speed. 
E)  at all times since it is a constant when the motor is running at any speed.

Question 4

A metal rod of length 2.0 m is moved at 6.0 m/s in a direction perpendicular to its length.A 5.0 m T magnetic field is perpendicular to both the rod and its velocity.If the resistance of the rod is 15 m$\Omega$, what is the current in the rod?

Accepted Answer

A)  0.0 A 
B)  1.0 A 
C)  2.0 A 
D)  4.0 A 
E)  8.0 A 
A)  0.0 A 
B)  1.0 A 
C)  2.0 A 
D)  4.0 A 
E)  8.0 A

Question 5

A conducting ring is placed such that it is lying flat in the x-y plane.A magnetic field exists in the +z direction,and its strength is decreasing with time.Which of the following occurs?

Accepted Answer

A)  No current is induced in the ring. 
B)  A current is induced,in the counter-clockwise direction,as viewed from above the x-y plane. 
C)  The situation is unclear because we do not know the initial conditions. 
D)  A current is induced,in the clockwise direction as viewed from above the x-y plane. 
A)  No current is induced in the ring. 
B)  A current is induced,in the counter-clockwise direction,as viewed from above the x-y plane. 
C)  The situation is unclear because we do not know the initial conditions. 
D)  A current is induced,in the clockwise direction as viewed from above the x-y plane.

Question 6

An ideal transformer has 200 turns on its primary and 12 turns on its secondary.If the power input to the transformer is 120 kW,what is the power output?

Accepted Answer

A)  0.600 kW 
B)  7.20 kW 
C)  10.0 kW 
D)  120 kW 
E)  240 kW 
A)  0.600 kW 
B)  7.20 kW 
C)  10.0 kW 
D)  120 kW 
E)  240 kW

Question 7

A conducting rod slides at 3.0 m/s on metal rails separated by 2.0 m.The 0.66 m T magnetic field is into the paper.If the resistance is 220 m$\Omega$, what is the current in the circuit?

Accepted Answer

A)  18 mA 
B)  9.0 mA 
C)  87 $\mu$A 
D)  3.0 $\mu$A 
E)  4.5 mA 
A)  18 mA 
B)  9.0 mA 
C)  87 $\mu$A 
D)  3.0 $\mu$A 
E)  4.5 mA

Question 8

If the rotation rate of a generator coil is doubled,what happens to the peak emf?

Accepted Answer

A)  it stays the same 
B)  it doubles 
C)  it quadruples 
D)  it halves 
E)  it quarters 
A)  it stays the same 
B)  it doubles 
C)  it quadruples 
D)  it halves 
E)  it quarters

Question 9

An ideal transformer supplies 100 kW of power to a 120 V circuit.If the input voltage is 10,000 V,what is the input current?

Accepted Answer

A)  1.20 mA 
B)  10.0 A 
C)  120 A 
D)  240 A 
E)  830 A 
A)  1.20 mA 
B)  10.0 A 
C)  120 A 
D)  240 A 
E)  830 A

Question 10

A series LR circuit includes a 9.00 V battery,a 30.0 mH inductor,and a resistance of 5.00 $\Omega$.What is the time constant of this circuit?

Accepted Answer

A)  115 s 
B)  170 s 
C)  4.20 ms 
D)  6.00 ms 
E)  8.30 ms 
A)  115 s 
B)  170 s 
C)  4.20 ms 
D)  6.00 ms 
E)  8.30 ms

Question 11

The south end of a bar magnet is pushed downward toward a wire loop in the plane of the paper.In which direction is the induced current,and which way is the induced magnetic field?

Accepted Answer

A)  clockwise,into the paper 
B)  clockwise,out of the paper 
C)  counter-clockwise,into the paper 
D)  counter-clockwise,out of the paper 
E)  There is no induced current. 
A)  clockwise,into the paper 
B)  clockwise,out of the paper 
C)  counter-clockwise,into the paper 
D)  counter-clockwise,out of the paper 
E)  There is no induced current.

Question 12

A series LR circuit includes a 9.0 V battery,a resistance of 0.50 $\Omega$,and an inductance of 0.80 H.What is the induced emf 2.0 s after the switch has been closed?

Accepted Answer

A)  0.0 
B)  9.0 V 
C)  5.2 V 
D)  2.6 V 
E)  19 mV 
A)  0.0 
B)  9.0 V 
C)  5.2 V 
D)  2.6 V 
E)  19 mV

Question 13

A 20 turn coil of area 10 cm2 is placed in a magnetic field so that the normal to its area is in the direction of the field.If the field has a value of 0.25 T,what is the total flux through the coil?

Accepted Answer

A)  0.0 
B)  5.0 $\times$ 10-3 T·m2 
C)  25 $\times$ 10-5 T·m2 
D)  50 T · m2 
E)  25 T · m2 
A)  0.0 
B)  5.0 $\times$ 10-3 T·m2 
C)  25 $\times$ 10-5 T·m2 
D)  50 T · m2 
E)  25 T · m2

Question 14

A metal rod of length 2.0 m is moved at 6.0 m/s in a direction perpendicular to its length.A 5.0 T magnetic field is perpendicular to both the rod and its velocity.What is the magnitude of the electric field in the rod?

Accepted Answer

A)  12 mV/m 
B)  60 mV/m 
C)  30 mV/m 
D)  15 mV/m 
E)  0.0 
A)  12 mV/m 
B)  60 mV/m 
C)  30 mV/m 
D)  15 mV/m 
E)  0.0

Question 15

A solenoid of length 2.8 cm and diameter 0.75 cm is wound with 160 turns per cm.When the current through the solenoid is 0.20 A,what is the magnetic flux through one of the windings of the solenoid?

Accepted Answer

A)  2.5 $\times$ 10-7 Wb 
B)  1.8 $\times$ 10-7 Wb 
C)  0.88 $\times$ 10-7 Wb 
D)  1.2 $\times$ 10-7 Wb 
A)  2.5 $\times$ 10-7 Wb 
B)  1.8 $\times$ 10-7 Wb 
C)  0.88 $\times$ 10-7 Wb 
D)  1.2 $\times$ 10-7 Wb

Question 16

A conducting rod slides at 4.0 m/s on metal rails separated by 2.0 m.If a current of 40 mA is generated in the circuit with resistance of 0.36 $\Omega$,what is the magnetic field between the rails?

Accepted Answer

A)  0.028 T 
B)  0.11 T 
C)  14 mT 
D)  3.6 mT 
E)  1.8 mT 
A)  0.028 T 
B)  0.11 T 
C)  14 mT 
D)  3.6 mT 
E)  1.8 mT

Question 17

What is the magnetic energy stored by a 300 mH inductor with a 2.0-A current going through it?

Accepted Answer

A)  0.60 J 
B)  1.2 J 
C)  30 mJ 
D)  0.15 J 
E)  0.075 J 
A)  0.60 J 
B)  1.2 J 
C)  30 mJ 
D)  0.15 J 
E)  0.075 J

Question 18

A circular coil lays flat on a horizontal table in a region where the magnetic field is straight down.The magnetic field is suddenly removed.When viewed from above,what is the direction of the current in the coil as the field is removed?

Accepted Answer

A)  clockwise 
B)  clockwise initially,then counter-clockwise before going to zero 
C)  counter-clockwise 
D)  There is no induced current. 
A)  clockwise 
B)  clockwise initially,then counter-clockwise before going to zero 
C)  counter-clockwise 
D)  There is no induced current.

Question 19

A coil is rotated in a magnetic field about an axis perpendicular to the field.During each rotation,how many times does the flux through the coil equal zero?

Accepted Answer

A)  0 
B)  1 
C)  2 
D)  4 
E)  more than 4 
A)  0 
B)  1 
C)  2 
D)  4 
E)  more than 4

Question 20

Faraday's law of induction states that the emf induced in a rectangular loop of wire is proportional to

Accepted Answer

A)  the magnetic flux. 
B)  the time variation of the magnetic flux. 
C)  current divided by the time. 
D)  the magnetic flux density times the area of the loop. 
A)  the magnetic flux. 
B)  the time variation of the magnetic flux. 
C)  current divided by the time. 
D)  the magnetic flux density times the area of the loop.

Exam 20: Electromagnetic Induction

An ideal solenoid has a length of 25 mm.If the windings are compressed so that the length is reduced to 1/2 of its original length how does the inductance change?

A series LR circuit includes a 9.0.V battery,a resistance of 0.500 Ω\OmegaΩ ,and an inductance of 0.800 H.What is the greatest energy stored by the inductor after the switch is closed?

The back emf of an electric motor is greatest

A metal rod of length 2.0 m is moved at 6.0 m/s in a direction perpendicular to its length.A 5.0 m T magnetic field is perpendicular to both the rod and its velocity.If the resistance of the rod is 15 m Ω\OmegaΩ , what is the current in the rod?

A conducting ring is placed such that it is lying flat in the x-y plane.A magnetic field exists in the +z direction,and its strength is decreasing with time.Which of the following occurs?

An ideal transformer has 200 turns on its primary and 12 turns on its secondary.If the power input to the transformer is 120 kW,what is the power output?

A conducting rod slides at 3.0 m/s on metal rails separated by 2.0 m.The 0.66 m T magnetic field is into the paper.If the resistance is 220 m Ω\OmegaΩ , what is the current in the circuit?

If the rotation rate of a generator coil is doubled,what happens to the peak emf?

An ideal transformer supplies 100 kW of power to a 120 V circuit.If the input voltage is 10,000 V,what is the input current?

A series LR circuit includes a 9.00 V battery,a 30.0 mH inductor,and a resistance of 5.00 Ω\OmegaΩ .What is the time constant of this circuit?

The south end of a bar magnet is pushed downward toward a wire loop in the plane of the paper.In which direction is the induced current,and which way is the induced magnetic field?

A series LR circuit includes a 9.0 V battery,a resistance of 0.50 Ω\OmegaΩ ,and an inductance of 0.80 H.What is the induced emf 2.0 s after the switch has been closed?

A 20 turn coil of area 10 cm2 is placed in a magnetic field so that the normal to its area is in the direction of the field.If the field has a value of 0.25 T,what is the total flux through the coil?

A metal rod of length 2.0 m is moved at 6.0 m/s in a direction perpendicular to its length.A 5.0 T magnetic field is perpendicular to both the rod and its velocity.What is the magnitude of the electric field in the rod?

A solenoid of length 2.8 cm and diameter 0.75 cm is wound with 160 turns per cm.When the current through the solenoid is 0.20 A,what is the magnetic flux through one of the windings of the solenoid?

A conducting rod slides at 4.0 m/s on metal rails separated by 2.0 m.If a current of 40 mA is generated in the circuit with resistance of 0.36 Ω\OmegaΩ ,what is the magnetic field between the rails?

What is the magnetic energy stored by a 300 mH inductor with a 2.0-A current going through it?

A circular coil lays flat on a horizontal table in a region where the magnetic field is straight down.The magnetic field is suddenly removed.When viewed from above,what is the direction of the current in the coil as the field is removed?

A coil is rotated in a magnetic field about an axis perpendicular to the field.During each rotation,how many times does the flux through the coil equal zero?

Faraday's law of induction states that the emf induced in a rectangular loop of wire is proportional to

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Filters

A series LR circuit includes a 9.0.V battery,a resistance of 0.500 $\Omega$ ,and an inductance of 0.800 H.What is the greatest energy stored by the inductor after the switch is closed?

A metal rod of length 2.0 m is moved at 6.0 m/s in a direction perpendicular to its length.A 5.0 m T magnetic field is perpendicular to both the rod and its velocity.If the resistance of the rod is 15 m $\Omega$ , what is the current in the rod?

A series LR circuit includes a 9.00 V battery,a 30.0 mH inductor,and a resistance of 5.00 $\Omega$ .What is the time constant of this circuit? $A series LR circuit includes a 9.00 V battery,a 30.0 mH inductor,and a resistance of 5.00 \Omega .What is the time constant of this circuit?$

A series LR circuit includes a 9.0 V battery,a resistance of 0.50 $\Omega$ ,and an inductance of 0.80 H.What is the induced emf 2.0 s after the switch has been closed?

A 20 turn coil of area 10 cm² is placed in a magnetic field so that the normal to its area is in the direction of the field.If the field has a value of 0.25 T,what is the total flux through the coil?