Question 1

The frequency of a microwave signal is 9.76 GHz. What is its wavelength? (c = 3.00 × 108 m/s)

Accepted Answer

A)  3.07 cm 
B)  2.07 cm 
C)  1.07 cm 
D)  5.07 cm 
E)  4.07 cm 
A)  3.07 cm 
B)  2.07 cm 
C)  1.07 cm 
D)  5.07 cm 
E)  4.07 cm A

Question 2

According to Lenz's law, the induced current in a circuit always flows to oppose the external magnetic field through the circuit.

Accepted Answer

A) True 
 B)False  False

Question 3

Which one of the following is not an electromagnetic wave?

Accepted Answer

A)  ultraviolet 
B)  infrared 
C)  radio waves 
D)  sound waves 
E)  gamma rays 
A)  ultraviolet 
B)  infrared 
C)  radio waves 
D)  sound waves 
E)  gamma rays D

Question 4

Which of the following actions will increase the energy of a photon? (There could be more than one correct choice.)

Accepted Answer

A)  Increase its wavelength. 
B)  Increase its frequency. 
C)  Decrease its wavelength. 
D)  Decrease its frequency. 
E)  Increase its speed. 
A)  Increase its wavelength. 
B)  Increase its frequency. 
C)  Decrease its wavelength. 
D)  Decrease its frequency. 
E)  Increase its speed.

Question 5

A circular coil lies flat on a horizontal surface. A bar magnet is held fixed above the center of the coil with its north pole pointing downward. What is the direction of the induced current in the coil, as viewed from above?

Accepted Answer

A)  clockwise 
B)  counterclockwise 
C)  There is no current in the coil. 
A)  clockwise 
B)  counterclockwise 
C)  There is no current in the coil.

Question 6

The human eye can just detect green light of wavelength 500 nm if it arrives at the retina at the rate of 2 × 10-18 W. How many photons arrive each second? (c = 3.0 × 108 m/s, h = 6.626 × 10-34 J ∙ s)

Accepted Answer

Question 7

A long straight wire lies on a horizontal table and carries an ever-increasing current toward the north. Two coils of wire lie flat on the table, one on either side of the wire. When viewed from above, the direction of the induced current in these coils is

Accepted Answer

A)  clockwise in both coils. 
B)  counterclockwise in both coils. 
C)  clockwise in the east coil and counterclockwise in the west coil. 
D)  counterclockwise in the east coil and clockwise in the west coil. 
A)  clockwise in both coils. 
B)  counterclockwise in both coils. 
C)  clockwise in the east coil and counterclockwise in the west coil. 
D)  counterclockwise in the east coil and clockwise in the west coil.

Question 8

As shown in the figure, a large round loop of 269 turns and radius 67.0 cm carries a current of I = $78.0 \mathrm {~A}$ A small square loop of 31.0 turns and 1.00 cm on a side is placed at the center of the large loop. If the current in the large loop drops to 0.00 A in 0.0470 s, find the induced emf in the small loop. The square loop is small enough that you can assume that the magnetic field in its region is uniform and equal to the magnetic field at the center of the round loop. (μ0 = 4π × 10-7 T ∙ m/A)

Accepted Answer

Question 9

The amplitude of the electric field for a certain type of electromagnetic wave is 570 N/C. What is the amplitude of the magnetic field for that wave? (c = 3.00 × 108 m/s)

Accepted Answer

A)  2.91 µT 
B)  1.90 µT 
C)  1.10 µT 
D)  1.41 µT 
E)  2.41 µT 
A)  2.91 µT 
B)  1.90 µT 
C)  1.10 µT 
D)  1.41 µT 
E)  2.41 µT

Question 10

An electromagnetic wave is propagating towards the west in free space. At a certain moment the direction of the magnetic field vector associated with this wave points vertically upward. What is the direction of the electric field vector?

Accepted Answer

A)  horizontal and pointing south 
B)  vertical and pointing down 
C)  horizontal and pointing north 
D)  vertical and pointing upward 
E)  horizontal and pointing east 
A)  horizontal and pointing south 
B)  vertical and pointing down 
C)  horizontal and pointing north 
D)  vertical and pointing upward 
E)  horizontal and pointing east

Question 11

An electromagnetic wave travels in free space in the +y direction, as shown in the figure. If the electric field at the origin is along the +z direction, what is the direction of the magnetic field?

Accepted Answer

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

Question 12

As shown in the figure, a straight wire carries a current I into the page. The wire passes through the center of a toroidal coil. If the current I is quickly reduced to zero, the direction of the induced current through the resistor R is

Accepted Answer

A)  from a to b. 
B)  from b to a. 
C)  No current is induced. 
A)  from a to b. 
B)  from b to a. 
C)  No current is induced.

Question 13

Unpolarized light of intensity I0 passes through four ideal polarizing sheets. The polarizing angle of each sheet is rotated 30° from the one before it, so that the last sheet is aligned at 90° to the first sheet. What is the intensity of the light emerging from the fourth sheet in terms of I0?

Accepted Answer

Question 14

The rate of energy flow per unit area of a sinusoidal electromagnetic wave has an average value of 0.601 W/m2. What is the maximum value of the magnetic field in the wave? 
(c = 3.00 × 108 m/s, μ0 = 4π × 10-7 T ∙ m/A, ε0 = 8.85 × 10-12 C2/N ∙ m2)

Accepted Answer

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

Question 15

An 800-kHz sinusoidal radio signal is detected at a point 6.6 km from the transmitter tower. The electric field amplitude of the signal at that point is 0.780 V/m. Assume that the signal power is radiated uniformly in all directions and that radio waves incident upon the ground are completely absorbed. What is the amplitude of the magnetic field of the signal at that point? (ε0 = 8.85 × 10-12 C2/N ∙ m2, c = 3.0 × 108 m/s, μ0 = 4π × 10-7 T ∙ m/A)

Accepted Answer

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

Question 16

An x-ray tube accelerates electrons through a potential difference of 50.0 kV. If an electron in the beam suddenly give up its energy in a collision, what is the shortest wavelength x-ray it could produce? (c = 3.00 × 108 m/s, h = 6.626 × 10-34 J ∙ s, e = 1.60 × 10-19C)

Accepted Answer

Question 17

An outer metal ring surrounds an inner metal ring, as shown in the figure. The current in the outer ring is counterclockwise and decreasing. What is the direction of the induced current in the inner ring?

Accepted Answer

A)  clockwise 
B)  counterclockwise 
C)  There is no induced current in the inner ring. 
A)  clockwise 
B)  counterclockwise 
C)  There is no induced current in the inner ring.

Question 18

The wire in the figure carries a steady current I. What is true about the currents induced in each of the three loops shown? The wire and the three loops are all in the same plane.

Accepted Answer

A)  No current is induced in any loop. 
B)  The currents are counterclockwise in all three loops. 
C)  The currents are clockwise in all three loops. 
D)  Loop A has clockwise current, loop B has no induced current, and loop C has counterclockwise current. 
E)  Loop A has counterclockwise current, loop B has no induced current, and loop C has clockwise current. 
A)  No current is induced in any loop. 
B)  The currents are counterclockwise in all three loops. 
C)  The currents are clockwise in all three loops. 
D)  Loop A has clockwise current, loop B has no induced current, and loop C has counterclockwise current. 
E)  Loop A has counterclockwise current, loop B has no induced current, and loop C has clockwise current.

Question 19

What are the wavelength and the corresponding photon energy (in electron-volts) of the primary light emitted by an ideal blackbody at each of the following temperatures? (c = 3.00 × 108 m/s, h = 6.626 × 10-34 J ∙ s, 1 eV = 1.60 × 10-19 J, and the constant in Wein's law is 0.00290 m ∙ K)
(a) 400°C?
(b) 800°C?
(c) 1200°C?

Accepted Answer

(a) 4.31 μm, 0.288 e

Question 20

For a beam of light, the direction of polarization is defined as

Accepted Answer

A)  the beam's direction of travel. 
B)  the direction of the electric field's vibration. 
C)  the direction of the magnetic field's vibration. 
D)  the direction that is perpendicular to both the electric and magnetic field vectors. 
A)  the beam's direction of travel. 
B)  the direction of the electric field's vibration. 
C)  the direction of the magnetic field's vibration. 
D)  the direction that is perpendicular to both the electric and magnetic field vectors.

Exam 25: EM Induction and Em Waves

The frequency of a microwave signal is 9.76 GHz. What is its wavelength? (c = 3.00 × 108 m/s)

According to Lenz's law, the induced current in a circuit always flows to oppose the external magnetic field through the circuit.

Which one of the following is not an electromagnetic wave?

Which of the following actions will increase the energy of a photon? (There could be more than one correct choice.)

A circular coil lies flat on a horizontal surface. A bar magnet is held fixed above the center of the coil with its north pole pointing downward. What is the direction of the induced current in the coil, as viewed from above?

The human eye can just detect green light of wavelength 500 nm if it arrives at the retina at the rate of 2 × 10-18 W. How many photons arrive each second? (c = 3.0 × 108 m/s, h = 6.626 × 10-34 J ∙ s)

A long straight wire lies on a horizontal table and carries an ever-increasing current toward the north. Two coils of wire lie flat on the table, one on either side of the wire. When viewed from above, the direction of the induced current in these coils is

The amplitude of the electric field for a certain type of electromagnetic wave is 570 N/C. What is the amplitude of the magnetic field for that wave? (c = 3.00 × 108 m/s)

An electromagnetic wave is propagating towards the west in free space. At a certain moment the direction of the magnetic field vector associated with this wave points vertically upward. What is the direction of the electric field vector?

An electromagnetic wave travels in free space in the +y direction, as shown in the figure. If the electric field at the origin is along the +z direction, what is the direction of the magnetic field?

As shown in the figure, a straight wire carries a current I into the page. The wire passes through the center of a toroidal coil. If the current I is quickly reduced to zero, the direction of the induced current through the resistor R is

Unpolarized light of intensity I0 passes through four ideal polarizing sheets. The polarizing angle of each sheet is rotated 30° from the one before it, so that the last sheet is aligned at 90° to the first sheet. What is the intensity of the light emerging from the fourth sheet in terms of I0?

The rate of energy flow per unit area of a sinusoidal electromagnetic wave has an average value of 0.601 W/m2. What is the maximum value of the magnetic field in the wave? (c = 3.00 × 108 m/s, μ0 = 4π × 10-7 T ∙ m/A, ε0 = 8.85 × 10-12 C2/N ∙ m2)

An x-ray tube accelerates electrons through a potential difference of 50.0 kV. If an electron in the beam suddenly give up its energy in a collision, what is the shortest wavelength x-ray it could produce? (c = 3.00 × 108 m/s, h = 6.626 × 10-34 J ∙ s, e = 1.60 × 10-19C)

An outer metal ring surrounds an inner metal ring, as shown in the figure. The current in the outer ring is counterclockwise and decreasing. What is the direction of the induced current in the inner ring?

The wire in the figure carries a steady current I. What is true about the currents induced in each of the three loops shown? The wire and the three loops are all in the same plane.

For a beam of light, the direction of polarization is defined as

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Filters

The frequency of a microwave signal is 9.76 GHz. What is its wavelength? (c = 3.00 × 10⁸ m/s)

The human eye can just detect green light of wavelength 500 nm if it arrives at the retina at the rate of 2 × 10^-18 W. How many photons arrive each second? (c = 3.0 × 10⁸ m/s, h = 6.626 × 10^-34 J ∙ s)

The amplitude of the electric field for a certain type of electromagnetic wave is 570 N/C. What is the amplitude of the magnetic field for that wave? (c = 3.00 × 10⁸ m/s)

The rate of energy flow per unit area of a sinusoidal electromagnetic wave has an average value of 0.601 W/m². What is the maximum value of the magnetic field in the wave? (c = 3.00 × 10⁸ m/s, μ₀ = 4π × 10^-7 T ∙ m/A, ε₀ = 8.85 × 10^-12 C²/N ∙ m²)

An x-ray tube accelerates electrons through a potential difference of 50.0 kV. If an electron in the beam suddenly give up its energy in a collision, what is the shortest wavelength x-ray it could produce? (c = 3.00 × 10⁸ m/s, h = 6.626 × 10^-34 J ∙ s, e = 1.60 × 10^-19C)