Deck 21: Alternating-Current Circuits and Electromagnetic Waves: Part A

Question 1

An airplane with a wingspan of 60.0 m flies parallel to the Earth's surface at a point where the downward component of the Earth's magnetic field is 0.400 × l0−⁴ T.If the induced potential between wingtips is 0.600 V,what is the plane's speed?

A) 338 m/s
B) 375 m/s
C) 250 m/s
D) 417 m/s

Answer 1

250 m/s

Question 2

A 10-turn square coil of area 0.036 m² and a 6-turn circular coil are both placed at an angle of 25° to the same changing magnetic field.The voltage induced in each of the coils is the same.What is the area of the circular coil?

A) 0.072 m².
B) 0.060 m²
C) 0.072 m²
D) 0.60 m²

Answer 2

0.060 m²

Question 3

The magnetic field inside a circular loop of wire of radius 30 cm increases at a constant rate from 2.0 × 10^-3 T to 3.5 × 10^-3 T in 0.47 s.If the resistance of the loop is 0.31 Ω,what is the current in the loop?

A) 7.4 × 10^-4 A
B) 5.8 × 10^-4 A
C) 2.9 × 10^-3 A
D) 5.8 × 10^-3 A

Answer 3

2.9 × 10^-3 A

Question 4

A coil in a magnetic field encloses a flux of 0.256 T·m² when the angle between the normal to the coil and the direction of the magnetic field is 70.0°.What flux would go through the coil if the angle were changed to 30.0°?

A) 0.648 T·m²
B) 0.573 T·m²
C) 0.114 T·m²
D) 0.198 T·m²

Question 5

A circular loop of wire has its radius doubled in time Ät.A uniform magnetic field is at an angle of 60^° to the plane of the coil,and the magnetic field halves its intensity in the same time interval Ät.During this interval,what happens to the flux through the coil?

A) It decreases.
B) It remains the same.
C) It increases.
D) More information is needed to make this conclusion.

Question 6

The magnetic field inside a circular loop of wire of radius 30 cm increases at a constant rate from 2.0 × 10^-3 T to 3.5 × 10^-3 T in 0.47 s.What is the induced emf in the wire?

A) 9.0 ×10^-4 V
B) 2.3 ×10^-4 V
C) 1.8 ×10^-3 V
D) 1.8 ×10^-4 V

Question 7

A loop of area 0.250 m² is in a uniform 0.0200-T magnetic field.If the flux through the loop is 3.21 × 10^-3 T·m²,what angle does the normal to the plane of the loop make with the direction of the magnetic field?

A) 40.0°
B) 37.5°
C) 50.0°
D) This is not possible.

Question 8

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 60% 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?

A) It must increase by 60%.
B) It must increase by 120%.
C) It must decrease by 40%.
D) It must increase by 67%.

Question 9

A flat coil of wire consisting of 20 turns,each with an area of 80 cm²,is positioned perpendicularly to a uniform magnetic field that increases its magnitude at a constant rate from 2.0 T to 6.0 T in 2.0 s.If the coil has a total resistance of 0.40 Ω,what is the magnitude of the induced current?

A) 500 mA
B) 70 mA
C) 140 mA
D) 800 mA

Question 10

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

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

Question 11

A large jetliner with a wingspan of 40 m flies horizontally and due north at a speed of 300 m/s in a region where the magnetic field of the earth is 51 µT directed 24.1° below the horizontal.What is the magnitude of the induced emf between the ends of the wing?

A) 350 mV
B) 750 mV
C) 550 mV
D) 250 mV

Question 12

The current in a coil with a self-inductance of 1.5 mH increases from 0 to 2.0 A in a tenth of a second.What is the induced emf in the coil?

A) 15 mV
B) 0.30 V
C) 0.10 V
D) 30 mV

Question 13

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 doubles?

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

Question 14

A uniform 1.5-T magnetic field passes perpendicularly through the plane of a wire loop 0.30 m² in area.What flux passes through the loop?

A) 0.135 T⋅m²
B) 5.0 T⋅m²
C) 0.45 T⋅m²
D) 0.25 T⋅m²

Question 15

A planar loop consisting of four turns of wire,each of which encloses 250 cm²,is oriented perpendicularly to a magnetic field that increases uniformly in magnitude from 10 mT to 25 mT in a time of 5.0 ms.What is the resulting induced current in the coil if the resistance of the coil is 5.0 Ω?

A) 48 mA
B) 0.24 mA
C) 12 mA
D) 60 mA

Question 16

A uniform 4.5-T magnetic field passes through the plane of a wire loop 0.20 m² in area.What flux passes through the loop when the direction of the 4.5-T field is at a 30° angle to the normal of the loop plane?

A) 0.39 T⋅m²
B) 5.0 T⋅m²
C) 0.78 T⋅m²
D) 0.225 T⋅m²

Question 17

A coil with a self-inductance of 0.75 mH experiences a constant current buildup from zero to 15 A in 0.25 s.What is the induced emf during this interval?

A) 0.045 V
B) 0.47 V
C) 0.030 V
D) 0.019 V

Question 18

A 0.200-m wire is moved parallel to a 0.500-T magnetic field at a speed of 6.00 m/s.What emf is induced across the ends of the wire?

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

Question 19

Three loops of wire,one circular,one rectangular,and one square,are made from identical lengths of wire.If the loops are in the same increasing magnetic field perpendicular to the plane of the coils,which loop has the least induced emf?

A) the square one
B) the rectangular one
C) the circular one
D) All three would have the same emf induced.

Question 20

A square coil,enclosing an area with sides 3.0 cm long,is wrapped with 2500 turns of wire.A uniform magnetic field perpendicular to its plane is turned on and increases to 0.12 T during an interval of 1.0 s.What average voltage is induced in the coil?

A) 2.5 V
B) 0.27 V
C) 1.2 V
D) 0.12 V

Question 21

The first solenoid has 2 times the diameter,2 times the number of turns,and 2 times the length of the second solenoid.Which solenoid has the greater inductance and by what factor?

A) the first solenoid by a factor of 8
B) the second solenoid by a factor of 8
C) the first solenoid by a factor of 16
D) the second solenoid by a factor of 32

Question 22

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?

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 23

An RL circuit has L = 0.40 H and R = 5.0 Ω.It is connected to a battery with ε = 22 V at time t = 0.Find the energy stored in the inductor when the current in the circuit is 2.3 A.

A) 5.0 J
B) 2.0 J
C) 50 mJ
D) 1.1 J

Question 24

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.The current in the primary at this moment is 6 A and increasing.The current in the secondary must be:

A) 3 A.
B) 6 A.
C) zero.
D) There is insufficient information to work this problem.

Question 25

What is the self-inductance in a coil that experiences a 3.0-V induced emf when the current is changing at a rate of 37 A/s?

A) 81 mH
B) 37 mH
C) 27 mH
D) 45 mH

Question 26

By what factor does the maximum energy stored in a series RL circuit change if the resistance is doubled and the inductance is tripled in the circuit?

A) 0.67
B) 0.75
C) 0.50
D) 1.5

Question 27

By what factor is the self-inductance of a solenoid changed if only its number of coil turns,N,is doubled?

A) 8
B) 1/2
C) 4
D) 2

Question 28

An inductor has 1000 turns/m and an internal volume of 30 cm³.What is its inductance?

A) 0.38 H
B) 38 μH
C) 3.8 μH
D) Insufficient information is given.

Question 29

By what factor is the self-inductance of a solenoid changed if its length is doubled and its number of coil turns is tripled?

A) 2/9
B) 9/2
C) 3/4
D) 4/3

Question 30

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 6 A,the current in the secondary will be:

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

Question 31

Which of the following is referred to as mutual inductance?

A) Two unconnected inductors have their coils wound in the same pattern.
B) Two solenoids have the same inductance.
C) The changing flux from one inductor produces an emf in another inductor.
D) The numerical value of one inductance is the reciprocal of another inductance in the same circuit.

Question 32

By what factor is the self-inductance of a solenoid changed if only its cross-sectional area,A,is doubled?

A) 1/2
B) 4
C) 2
D) 8