Question 1

The SI unit H (the henry)is equal to a

Accepted Answer

A)  V/m. 
B)  V/A. 
C)  V·s. 
D)  V·s/A. 
E)  V·A/s. 
A)  V/m. 
B)  V/A. 
C)  V·s. 
D)  V·s/A. 
E)  V·A/s.

Question 2

A generator has 200 turns of wire on a coil of radius 2.00 cm.What rotational speed is necessary to produce an emf of amplitude 4.50 V if the magnetic field in the region of the coil is 0.180 T?

Accepted Answer

A)  60.0 rad/s 
B)  16.0 rpm 
C)  100 rpm 
D)  500 rpm 
E)  950 rpm 
A)  60.0 rad/s 
B)  16.0 rpm 
C)  100 rpm 
D)  500 rpm 
E)  950 rpm

Question 3

For the typical "household ac voltage" of 120 V,what is the amplitude of the emf?

Accepted Answer

A)  120 V 
B)  240 V 
C)  60.0 V 
D)  170 V 
E)  330 V 
A)  120 V 
B)  240 V 
C)  60.0 V 
D)  170 V 
E)  330 V

Question 4

Lenz's law arises because of the following basic principle:

Accepted Answer

A)  Gauss's law 
B)  the conservation of momentum 
C)  Coulomb's law 
D)  the conservation of energy 
E)  the conservation of charge 
A)  Gauss's law 
B)  the conservation of momentum 
C)  Coulomb's law 
D)  the conservation of energy 
E)  the conservation of charge

Question 5

Doubling the diameter of a loop of wire produces what change of induced emf?

Accepted Answer

A)  The induced emf is 4 times as much. 
B)  The induced emf is twice as much. 
C)  There is no change in the induced emf. 
D)  The induced emf is 6.28 times as much. 
A)  The induced emf is 4 times as much. 
B)  The induced emf is twice as much. 
C)  There is no change in the induced emf. 
D)  The induced emf is 6.28 times as much.

Question 6

A square conducting loop is situated such that it is vertical,in the x-z plane.The earth's gravitational field points downward (in the -z direction).The loop is dropped,and maintains its orientation in the x-z plane.A magnetic field pointing in the +y direction exists and is uniform with respect to time,but varies as a function of z: B(z) = Bo(10 m - z).The loop is dropped and allowed to fall under the influence of gravitation.You observe the loop from the +y direction.Which of the following occurs?

Accepted Answer

A)  The situation is unclear because we do not know the initial conditions. 
B)  There is a clockwise induced current. 
C)  There is a counter-clockwise induced current. 
D)  There is no induced current. 
A)  The situation is unclear because we do not know the initial conditions. 
B)  There is a clockwise induced current. 
C)  There is a counter-clockwise induced current. 
D)  There is no induced current.

Question 7

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 energy stored by the inductor 2.0 s after the switch is closed?

Accepted Answer

A)  33 mJ 
B)  30 mJ 
C)  13 J 
D)  66 J 
E)  33 J 
A)  33 mJ 
B)  30 mJ 
C)  13 J 
D)  66 J 
E)  33 J

Question 8

Electric fields that arise from changing magnetic fields have all the properties below except:

Accepted Answer

A)  They terminate on electric charges. 
B)  They cannot be described by an electric potential. 
C)  Their field lines take the form of closed loops. 
D)  Work done by the field along a closed path may be non-zero. 
A)  They terminate on electric charges. 
B)  They cannot be described by an electric potential. 
C)  Their field lines take the form of closed loops. 
D)  Work done by the field along a closed path may be non-zero.

Question 9

What is the magnetic energy density in a volume where the magnetic field is 4.0 mT?

Accepted Answer

A)  3.2 $\times$ 10-3 J/m3 
B)  3.2 J/m3 
C)  6.4 J/m3 
D)  13 J/m3 
E)  13 $\times$ 10-3 J/m3 
A)  3.2 $\times$ 10-3 J/m3 
B)  3.2 J/m3 
C)  6.4 J/m3 
D)  13 J/m3 
E)  13 $\times$ 10-3 J/m3

Question 10

A dc motor is connected to a emf of 12.0 V.The resistance of its windings is 2.0 $\Omega$.At normal operating speed,the motor delivers 6.0 W of mechanical power.What current does it draw at normal operating speed?

Accepted Answer

A)  6.0 A 
B)  0.50 A 
C)  1.0 A 
D)  3.0 A 
A)  6.0 A 
B)  0.50 A 
C)  1.0 A 
D)  3.0 A

Question 11

A generator is designed to produce a maximum emf of 170 V while rotating at 3200 rpm.The 1525 coils of the generator are circular with diameter 7.5 cm.Assuming the magnetic field in the generator is 0.075 T,what is the necessary magnetic field for the generator?

Accepted Answer

A)  0.0079 T 
B)  0.30 T 
C)  0.075 T 
D)  0.24 T 
A)  0.0079 T 
B)  0.30 T 
C)  0.075 T 
D)  0.24 T

Question 12

A horizontal desk surface measures 1.3 m by 1.0 m.If the Earth's magnetic field has a magnitude of 0.44 mT and is directed 65$^{\circ}$below the horizontal,what is the magnetic flux through the desk surface?

Accepted Answer

A)  1.1 $\times$ 10-3 Wb 
B)  5.2 $\times$ 10-4 Wb 
C)  3.2 $\times$ 10-4 Wb 
D)  7.3 $\times$ 10-3 Wb 
A)  1.1 $\times$ 10-3 Wb 
B)  5.2 $\times$ 10-4 Wb 
C)  3.2 $\times$ 10-4 Wb 
D)  7.3 $\times$ 10-3 Wb

Question 13

An ideal transformer has an input voltage of 20,000 V and an output voltage of 260 V.If the input current is 26.0 A,what is the output current?

Accepted Answer

A)  1.70 A 
B)  10.0 A 
C)  100 A 
D)  200 A 
E)  2000 A 
A)  1.70 A 
B)  10.0 A 
C)  100 A 
D)  200 A 
E)  2000 A

Question 14

A series LR circuit consists of a battery,resistor,inductor and a switch.When the switch is closed the circuit has a time constant of 8.0 s.If the resistance and inductance of the circuit are both doubled,what is the resulting time constant?

Accepted Answer

A)  8.0 s 
B)  16 s 
C)  32 s 
D)  4.0 s 
E)  2.0 s 
A)  8.0 s 
B)  16 s 
C)  32 s 
D)  4.0 s 
E)  2.0 s

Question 15

A 33 mH inductor has a current going through it that is increasing at a rate of 2.3 A/s.What is the magnitude of the induced emf in this coil?

Accepted Answer

A)  33 mV 
B)  76 mV 
C)  13 mV 
D)  95 mV 
E)  2.5 V 
A)  33 mV 
B)  76 mV 
C)  13 mV 
D)  95 mV 
E)  2.5 V

Question 16

The current in a 0.40 H inductor increases form 2.0 A to 3.0 A in 1.5 s.The energy stored by the inductor during this process increases by

Accepted Answer

A)  3.6 J. 
B)  1.8 J. 
C)  1.2 J. 
D)  1.0 J. 
E)  0.6 J. 
A)  3.6 J. 
B)  1.8 J. 
C)  1.2 J. 
D)  1.0 J. 
E)  0.6 J.

Question 17

An LR circuit is prepared for an experiment,initially with its switch open.The time constant is that time after switch closure at which the energy stored in the inductor reaches what percentage of its final value

Accepted Answer

A)  63% 
B)  14% 
C)  37% 
D)  40% 
E)  100% 
A)  63% 
B)  14% 
C)  37% 
D)  40% 
E)  100%

Question 18

The maximum induced emf in a generator whose coils are rotating at 240 rpm is 35 V.If,instead,it is desired to generate a maximum emf of 45 V but with half the magnetic field,what rotation rate must be used?

Accepted Answer

A)  380 rpm 
B)  190 rpm 
C)  310 rpm 
D)  165 rpm 
E)  610 rpm 
A)  380 rpm 
B)  190 rpm 
C)  310 rpm 
D)  165 rpm 
E)  610 rpm

Question 19

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 originally has a value of 0.25 T that increases to 0.35 T in 2.0 s,what is the average emf induced in the coil?

Accepted Answer

A)  7.0 mV 
B)  2.0 mV 
C)  1.0 mV 
D)  3.5 mV 
E)  4.0 mV 
A)  7.0 mV 
B)  2.0 mV 
C)  1.0 mV 
D)  3.5 mV 
E)  4.0 mV

Question 20

If the number of turns is tripled for an inductor of fixed length and fixed cross-sectional area,what happens to its inductance?

Accepted Answer

A)  it stays the same 
B)  it triples 
C)  it becomes 9 times the original value 
D)  it decreases by a factor of 3 
E)  it decreases by a factor of 9 
A)  it stays the same 
B)  it triples 
C)  it becomes 9 times the original value 
D)  it decreases by a factor of 3 
E)  it decreases by a factor of 9

Exam 20: Electromagnetic Induction

The SI unit H (the henry)is equal to a

A generator has 200 turns of wire on a coil of radius 2.00 cm.What rotational speed is necessary to produce an emf of amplitude 4.50 V if the magnetic field in the region of the coil is 0.180 T?

For the typical "household ac voltage" of 120 V,what is the amplitude of the emf?

Lenz's law arises because of the following basic principle:

Doubling the diameter of a loop of wire produces what change of induced emf?

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 energy stored by the inductor 2.0 s after the switch is closed?

Electric fields that arise from changing magnetic fields have all the properties below except:

What is the magnetic energy density in a volume where the magnetic field is 4.0 mT?

A dc motor is connected to a emf of 12.0 V.The resistance of its windings is 2.0 Ω\OmegaΩ .At normal operating speed,the motor delivers 6.0 W of mechanical power.What current does it draw at normal operating speed?

A generator is designed to produce a maximum emf of 170 V while rotating at 3200 rpm.The 1525 coils of the generator are circular with diameter 7.5 cm.Assuming the magnetic field in the generator is 0.075 T,what is the necessary magnetic field for the generator?

A horizontal desk surface measures 1.3 m by 1.0 m.If the Earth's magnetic field has a magnitude of 0.44 mT and is directed 65 ∘^{\circ}∘ below the horizontal,what is the magnetic flux through the desk surface?

An ideal transformer has an input voltage of 20,000 V and an output voltage of 260 V.If the input current is 26.0 A,what is the output current?

A series LR circuit consists of a battery,resistor,inductor and a switch.When the switch is closed the circuit has a time constant of 8.0 s.If the resistance and inductance of the circuit are both doubled,what is the resulting time constant?

A 33 mH inductor has a current going through it that is increasing at a rate of 2.3 A/s.What is the magnitude of the induced emf in this coil?

The current in a 0.40 H inductor increases form 2.0 A to 3.0 A in 1.5 s.The energy stored by the inductor during this process increases by

An LR circuit is prepared for an experiment,initially with its switch open.The time constant is that time after switch closure at which the energy stored in the inductor reaches what percentage of its final value

The maximum induced emf in a generator whose coils are rotating at 240 rpm is 35 V.If,instead,it is desired to generate a maximum emf of 45 V but with half the magnetic field,what rotation rate must be used?

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 originally has a value of 0.25 T that increases to 0.35 T in 2.0 s,what is the average emf induced in the coil?

If the number of turns is tripled for an inductor of fixed length and fixed cross-sectional area,what happens to its inductance?

Introduction

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Acceleration and Newtons Second Law of Motion

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Filters

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 energy stored by the inductor 2.0 s after the switch is closed?

A dc motor is connected to a emf of 12.0 V.The resistance of its windings is 2.0 $\Omega$ .At normal operating speed,the motor delivers 6.0 W of mechanical power.What current does it draw at normal operating speed?

A horizontal desk surface measures 1.3 m by 1.0 m.If the Earth's magnetic field has a magnitude of 0.44 mT and is directed 65 $^{\circ}$ below the horizontal,what is the magnetic flux through the desk surface?

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 originally has a value of 0.25 T that increases to 0.35 T in 2.0 s,what is the average emf induced in the coil?