Deck 25: Electromagnetic Induction and Electromagnetic Waves

Question 1

The energy flow per unit time per unit area (S)of an electromagnetic wave has an average value of 601 mW/m².The maximum value of the magnetic field in the wave is closest to:

A)7.09 × 10^-8 T
B)5.02 × 10^-8 T
C)3.55 × 10^-8T
D)9.81 × 10^-8 T
E)1.42 × 10^-7 T

Answer 1

7.09 × 10^-8 T

Question 2

What is the radius of a tightly wound solenoid of circular cross-section that has 180 turns if a change in its internal magnetic field of 3.0 T/s causes a 6.0 A current to flow? The resistance of the circuit that contains the solenoid is 17 Ω.The only emf source for the circuit is the induced emf.

A)0.25 m
B)0.014 m
C)0.54 m
D)0.043 m

Answer 2

0.25 m

Question 3

Light of intensity So and polarized horizontally passes through three polarizers.The first and third are horizontal,but the second is oriented 0.34907 rad to the horizontal.In terms of So,what is the intensity of the light that passes through the set of polarizers?

A)0.780 So
B)0.103 So
C)0.442 So
D)0.883 So

Answer 3

0.780 So

Question 4

If the peak electric field in an electromagnetic wave is 754 µV/m,what is the peak magnetic field for the same wave?

A)2.51 × 10^-12 T
B)7.53 T
C)7.54 × 10^-4 T
D)3.98 × 10¹¹ T

Question 5

A conductor is formed into a loop that encloses an area of 1.0 m².The loop is oriented at a 30.0º angle with the xy-plane.A varying magnetic field is oriented parallel to the z-axis.If the maximum emf induced in the loop is 25.0 V,what is the maximum rate at which the magnetic field strength is changing?

A)29 T/s
B)22 T/s
C)50 T/s
D)13 T/s

Question 6

Unpolarized light is incident upon two polarization filters that do not have their transmission axes aligned.If 14% of the light passes through,what is the measure of the angle between the transmission axes of the filters?

A)58°
B)75°
C)86°
D)82°

Question 7

A 7.55 × 10¹⁴ Hz electromagnetic wave propagates in carbon tetrachloride with a speed of 2.05 × 10⁸ m/s.The wavelength of the wave in carbon tetrachloride is closest to:

A)272 nm
B)301 nm
C)338 nm
D)361 nm
E)397 nm

Question 8

A circular coil of 20 turns and radius 5 cms is placed with its plane oriented at 90° to a magnetic field of 0.1 T.The field is now increased at a steady rate,reaching a value of 0.5 T after 4 seconds.What emf is induced in the coil?

A)0.016 V
B)0.021 V
C)0.026 V
D)0.031 V
E)0.036 V

Question 9

An 800 kHz radio signal is detected at a point 6.6 km distant from a transmitter tower.The electric field amplitude of the signal at that point is 780 mV/m.Assume that the signal power is radiated uniformly in all directions and that radio waves incident upon the ground are completely absorbed.The magnetic field amplitude of the signal at that point,in nT,is closest to:

A)2.6
B)2.1
C)1.6
D)3.1
E)3.6

Question 10

A 1.90 × 10¹⁴ Hz electromagnetic wave propagates in carbon tetrachloride with a speed of 2.05 × 10⁸ m/s.The wavelength of the wave in vacuum is closest to:

A)1580 nm
B)1080 nm
C)1260 nm
D)1420 nm
E)1740 nm

Question 11

Polarized light passes through a polarizer.If the electric vector of the polarized light is horizontal what,in terms of the initial intensity S_o,is the intensity of the light that passes through a polarizer if the polarizer is tilted 0.393 rad from the horizontal?

A)0.853 S_o
B)0.147 S_o
C)0.191 S_o
D)0.011 S_o

Question 12

An 800 kHz radio signal is detected at a point 9.5 km distant from a transmitter tower.The electric field amplitude of the signal at that point is 230 mV/m.Assume that the signal power is radiated uniformly in all directions and that radio waves incident upon the ground are completely absorbed.The average electromagnetic energy density at that point is closest to:

A)2.3 × 10-13 J/m³
B)3.3 × 10-13 J/m³
C)4.7 × 10-13 J/m³
D)6.6 × 10-13 J/m³
E)9.4 × 10-13 J/m³

Question 13

A circular conducting loop with a radius of 1.00 m and a small gap filled with a 10.0 Ω resistor is oriented in the xy-plane.If a magnetic field of 2.0 T,making an angle of 30º with the z-axis,increases to 9.0 T in 2.0 s,what is the magnitude of the current that will be caused to flow in the conductor?

A)0.095 A
B)0.55 A
C)0.95 A
D)0.24 A

Question 14

In the figure,a wire and a 10 Ω resistor are used to form a circuit in the shape of a square, 20 cm by 20 cm.A uniform but nonsteady magnetic field is directed into the plane of the circuit.The magnitude of the magnetic field is decreased from 2.70 T to 0.90 T in a time interval of
96 ms.The average induced current and its direction through the resistor,in this time interval,are closest to:

A)75 mA,from b to a
B)45 mA,from b to a
C)75 mA,from a to b
D)45 mA,from a to b
E)110 mA,from a to b

Question 15

A transmitter is operating at an average of 4.00 kW of power.What is the average intensity of the signal 8.00 km from the transmitter?

A)4.97 μW/m²
B)2.49 μW/m²
C)0.00497 W/m²
D)0.00249 W/m²

Question 16

A 2.0 m conductor is formed into a square and placed in the horizontal xy-plane.A magnetic field is oriented 30.0º above the horizontal with a strength of 9.0 T.What is the magnetic flux through the conductor?

A)1.1 T ∙ m²
B)1.9 T ∙ m²
C)2.3 T ∙ m²
D)18 T ∙ m²

Question 17

An electromagnetic wave has a magnetic field with Brms of 9.0 uT.What is Erms for this wave?

A)2700 V/m
B)27 V/m
C)3.00 V/m
D)0.0300 V/m

Question 18

A uniform electric field perpendicular to a spherical surface of radius 5.00 cm is increasing at a rate of 4.0 V/m · µs.Find the displacement current through the spherical surface.

A)1.11 μA
B)142 μA
C)1853 nA
D)0.071 mA

Question 19

Unpolarized light passes through three polarizing filters.The first is oriented with a horizontal transmission axis,the second has its transmission axis π/7 radians from the horizontal,and the third has a vertical transmission axis.What percent of the light gets through?

A)7.6%
B)92.4%
C)50.0%
D)0%

Question 20

A closed-loop conductor with radius 2.0 m is located in a changing magnetic field.If the maximum emf induced in the loop is 2.0 V,what is the maximum rate at which the magnetic field strength is changing if the magnetic field is oriented perpendicular to the plane in which the loop lies?

A)0.16 T/s
B)1.0 T/s
C)0.080 T/s
D)2.0 T/s

Question 21

A changing magnetic field causes an electric field and a changing electric field causes a magnetic field.

Question 22

You are pulling a rectangular coil through a uniform static magnetic field that extends well beyond the boundary of the coil.The faster you pull this coil perpendicular to the field,the greater the emf that is induced in it.

Question 23

Find the wavelength (in nm)of a 5.83 eV photon.

A)213 nm
B)181 nm
C)234 nm
D)253 nm

Question 24

The speed of all electromagnetic waves through vacuum is equal to the reciprocal of the square root of μ_oε_o.

Question 25

It requires work to push a coil between the poles of a horseshoe magnet,and it also requires additional work to pull that coil out again.

Question 26

Situation 25.1
The following are positioned in sequence: A source of a beam of natural light of intensity Io;three ideal polarizers A,B,and C;and an observer.Polarizer axis angles are measured clockwise from the vertical,from the perspective of the observer.The axis angle of polarizer A is set at zero degrees (vertical),and the axis angle of polarizer C is set at 50 degrees.
In Situation 25.1,polarizer B is set so that the beam intensity is zero at the observer.The two possible axis angle settings of polarizer B are:

A)40° and 90°
B)40° and 130°
C)40° and 140°
D)90° and 130°
E)90° and 140°

Question 27

A circular metal loop surrounds an ideal solenoid such that the plane of the loop is perpendicular to the cylindrical axis of the solenoid.If the current in the solenoid is steadily increased,no emf is induced in the loop because the magnetic field outside an ideal solenoid is zero.

Question 28

What is the wavelength used by a radio station that broadcasts with a carrier frequency of 920 kHz?

A)22.6 m
B)226 m
C)326 m
D)175 m
E)276 m

Question 29

Situation 25.1
The following are positioned in sequence: A source of a beam of natural light of intensity Io;three ideal polarizers A,B,and C;and an observer.Polarizer axis angles are measured clockwise from the vertical,from the perspective of the observer.The axis angle of polarizer A is set at zero degrees (vertical),and the axis angle of polarizer C is set at 50 degrees.
In Situation 25.1,the axis angle of polarizer B is set at 120°.The ratio of the intensity of the beam at the observer to the intensity of the source is closest to:

A)0.015
B)0.020
C)0.025
D)0.030
E)0.035

Question 30

In the figure,the orientation of the transmission axis for each of three polarizing sheets is labeled relative to the vertical direction.A beam of light,polarized in the vertical direction,is incident on the first polarized with an intensity of 1000 W/m².What is the intensity of the beam after it has passed through the three polarizing sheets when θ₁ = 30º,θ₂ = 30º,and θ₃ = 60º?

A)141 W/m²
B)316 W/m²
C)433 W/m²
D)563 W/m²
E)188 W/m²

Question 31

A certain electromagnetic field traveling in vacuum has a maximum electric field of 1200 V/m.What is the maximum magnetic field of this wave?

A)3.4 × 10^-4 T
B)4.0 × 10^-6 T
C)2.2 × 10^-5 T
D)9.6 × 10^-6 T
E)8.7 × 10^-6 T

Question 32

A beam of light is linearly polarized in a vertical plane and has an intensity Io.The beam passes through an ideal polarizer and then through an ideal analyzer whose axis is set horizontally.The axis of the polarizer is set at 60° with the vertical.The ratio of the intensity of the final beam to I_o is closest to:

A)0.19
B)0.25
C)0.31
D)0.37
E)0.43

Question 33

Find the energy (in eV)of an optical photon of frequency 5.15 x 10¹⁴ Hz.

A)2.13 eV
B)1.30 eV
C)1.56 eV
D)2.62 eV

Question 34

A bar magnet is oriented vertically,and a flat coil with its plane oriented horizontally is located a short distance just below the bottom of this magnet.The instant after the magnet is dropped from rest,you observe that a counterclockwise current is induced in the coil,as viewed from below the coil.From this observation,you can conclude that the lower end of the magnet is a south pole.

Question 35

An 800 kHz radio signal is detected at a point 2.1 km distant from a transmitter tower.The electric field amplitude of the signal at that point is 800 mV/m.Assume that the signal power is radiated uniformly in all directions and that radio waves incident upon the ground are completely absorbed.The intensity of the radio signal at that point is closest to:

A)8.5 × 10-4 W/m²
B)1.2 × 10-3 W/m²
C)1.7 × 10-3 W/m²
D)6.0 × 10-4 W/m²
E)4.2 × 10-4 W/m²

Question 36

Situation 25.1
The following are positioned in sequence: A source of a beam of natural light of intensity Io;three ideal polarizers A,B,and C;and an observer.Polarizer axis angles are measured clockwise from the vertical,from the perspective of the observer.The axis angle of polarizer A is set at zero degrees (vertical),and the axis angle of polarizer C is set at 50 degrees.
In Situation 25.1,polarizer B is set so that the beam intensity at the observer is a maximum.The axis angle of polarizer B is:

A)0°
B)25°
C)50°
D)75°
E)100°

Question 37

According to Lenz's law,the induced current in a circuit must flow in such a direction to oppose the flux through that circuit.

Question 38

A large magnetic flux change through a coil must induce a greater emf in this coil than a small flux change.

Question 39

If a coil stays at rest in a very large static magnetic field,no emf is induced in this coil.

Question 40

What is the energy of a photon in light of 610 nm wavelength? Express your answer in eV.

A)2.04 eV
B)2.20 eV
C)1.87 eV
D)1.71 eV

Question 41

At a certain instant in time,an electromagnetic wave has in the -z direction and in the +y direction.In what direction does the wave propagate?

A)+x direction
B)-x direction
C)+y direction
D)-z direction
E)+z direction

Question 42

In the figure,a C-shaped conductor is in a uniform magnetic field B,which is increasing.The polarity of the induced emf in terminals X and Y is:

A)X and Y are at the same potential
B)X is positive and Y is negative
C)Y is positive and X is negative

Question 43

In the figure,a straight wire carries a steady current I.A bar is in contact with a pair of circular rails and rotates about the straight wire.The induced current through the resistor R is:

A)zero
B)from a to b
C)from b to a

Question 44

In the figure,a battery supplies a steady current to the solenoid on the left.The two solenoids are moving toward each other.The induced current through the resistor R is:

A)zero
B)from a to b
C)from b to a

Question 45

In the figure,one end of a bar is in contact with a circular rail and the other end is pivoted at P.A steady,uniform,magnetic field B is present.The bar rotates about P.The induced current through the resistor R is:

A)zero
B)from a to b
C)from b to a

Question 46

In the figure,a bar magnet moves away from the solenoid.The induced current through the resistor R is:

A)zero
B)from a to b
C)from b to a

Question 47

A circular wire ring is situated above a long straight wire,as shown in the figure.The straight wire has a current flowing to the right,and the current is increasing in time at a constant rate.Which statement is true?

A)There is an induced current in the wire ring,directed in clockwise orientation.
B)There is an induced current in the wire ring,directed in a counterclockwise orientation.
C)There is no induced current in the wire ring.

Question 48

For electromagnetic waves,the electric and magnetic fields are often given in the form of sine waves.Explain how this model of electromagnetic waves does not violate the conservation of energy,especially when the sine functions are zero.

Question 49

In the figure,a bar is in contact with a pair of parallel rails and is in motion with velocity ν.A uniform magnetic field is present.The induced current through the resistor R is:

A)zero
B)from a to b
C)from b to a

Question 50

In the figure,a bar is in contact with a pair of parallel rails.A steady,uniform,magnetic field B is present.The bar is in motion with velocity ν.The polarity of the induced emf in terminals X and Y is:

A)X and Y are at the same potential
B)X is positive and Y is negative
C)Y is positive and X is negative

Question 51

In the figure,a bar is in contact with a pair of parallel rails.A steady,uniform,magnetic field,perpendicular to the plane of the rails,is present.The bar is in motion with velocity ν.The induced current through the resistor R is:

A)zero
B)from a to b
C)from b to a

Question 52

In the figure,two parallel wires carry a current I in opposite directions.A rectangular loop is midway between the wires.The current I is decreasing.The induced current through the resistor R is:

A)zero
B)from a to b
C)from b to a

Question 53

In the figure,a loop carries a steady current I.A bar is in contact with a pair of circular rails and rotates about the center of the loop.The induced current through the resistor R is:

A)zero
B)from a to b
C)from b to a

Question 54

By how much are the electric and magnetic fields out of phase in an electromagnetic wave?

Question 55

In the figure,a long bar slides on two contact points and is in motion with velocity ν.A steady,uniform,magnetic field B is present.The induced current through the resistor R is:

A)zero
B)from a to b
C)from b to a

Question 56

In an electromagnetic wave,if the magnetic field points in the -x direction and the electric field points in the +z direction,the wave must be traveling in the +y direction.

Question 57

In the figure,two solenoids are side by side.The switch S,initially open,is closed.The induced current through the resistor R is:

A)zero
B)from a to b
C)from b to a

Question 58

In the figure,two solenoids are in line.The switch S,initially closed,is opened.The polarity of the induced emf in terminals X and Y is:

A)X and Y are at the same potential
B)X is positive and Y is negative
C)Y is positive and X is negative

Question 59

In the figure,a straight wire carries a current I.The wire passes through the center of a toroidal coil.The current is quickly reduced to zero.The induced current through the resistor R is:

A)zero
B)from a to b
C)from b to a

Question 60

What is the essential difference between microwaves and blue light?

A)One has an electric charge,the other does not.
B)One undergoes refraction,the other does not.
C)One is a form of radiation,the other is not.
D)Blue light is a beam of photons.Microwaves are not photons.
E)There is no essential difference in the nature of microwaves and blue light other than a difference in frequency and wavelength.

Question 61

A loop of wire is situated inside a large solenoid,with the plane of the loop initially perpendicular to the axis of the solenoid.Current can be made to flow through the loop of wire if

A)a constant current is flowing through the solenoid wire.
B)the current flowing through the solenoid is decreasing with time.
C)the loop of wire is rotating within the solenoid,and a constant current is flowing through the solenoid wire.
D)All of the above statements are true.
E)Only two of the above statements are true.

Question 62

A conducting bar is free to slide horizontally on the rails of a conducting frame,as shown in the figure.A lightbulb is attached to the right end of the rails.A spatially uniform magnetic field is oriented vertically (perpendicular to the horizontal plane of the rails and bar).Initially the bar is stationary.The strength of the magnetic field begins increasing in time at a constant rate,which induces a current through the bar,frame,and lightbulb.The bar begins to move due to the magnetic force exerted on it.Once the bar begins to move,the brightness of the lightbulb

A)stays the same.
B)increases.
C)decreases.
D)suddenly drops to zero.

Question 63

Two electromagnetic waves are traveling at the same speed.The wave with the higher wavelength

A)has a higher frequency than the other wave.
B)has a lower frequency than the other wave.
C)is traveling faster than the other wave.
D)is traveling slower than the other wave.

Question 64

A magnet,with its north pole pointed downwards,is falling down directly above a wire loop.As the magnet approaches the wire loop (before it passes through the loop),

A)an induced current flows through the wire loop,in a clockwise orientation (as seen from above).
B)an induced current flows through the wire loop,in a counterclockwise orientation (as seen from above).
C)no current flows through the wire loop.

Question 65

While a magnet is moved toward the end of a solenoid,a voltage difference is induced between the two ends of the solenoid wire.The voltage difference would be larger if

A)the speed of the magnet were increased.
B)the solenoid contained more loops (while having the same length).
C)the bar magnet produced a stronger magnetic field.
D)All of the above statements are true.
E)Only two of the above statements are true.

Question 66

Which type of electromagnetic wave travels through space the slowest?

A)All EM waves travel at the same speed.
B)radio waves
C)infrared
D)ultraviolet
E)microwaves