Deck 25: Electromagnetic Waves

Question 1

According to the law of Malus, the transmitted intensity of a polarized beam of light passing through a polarizer is unchanged for an angle of 90°.

Answer 1

False

Question 2

In an electromagnetic wave the and fields are oriented such that

A) they are parallel to one another and perpendicular to the direction of wave propagation.
B) they are parallel to one another and parallel to the direction of wave propagation.
C) they are perpendicular to one another and perpendicular to the direction of wave propagation.
D) they are perpendicular to one another and parallel to the direction of wave propagation.
E) None of the above answers is correct.

Answer 2

they are perpendicular to one another and perpendicular to the direction of wave propagation.

Question 3

Electromagnetic waves are transverse in nature.

Answer 3

True

Question 4

The physicist responsible for explaining the wave nature of light was

A) Sir Isaac Newton.
B) Michael Faraday.
C) Heinrich Hertz.
D) James Clerk Maxwell.
E) Gustav Kirchhoff

Question 5

The Doppler effect applies to sound waves but not to electromagnetic waves.

Question 6

The speed of electromagnetic waves through a vacuum is ten times the speed of sound in air.

Question 7

Electromagnetic waves in a vacuum travel with the speed of light.

Question 8

Electromagnetic waves are longitudinal.

Question 9

The intensity of the radiation field of an antenna is inversely proportional to the distance from the antenna.

Question 10

The magnitude of the electric field in the radiation field from an antenna is inversely proportional to the distance from the antenna.

Question 11

The transmitted intensity of an unpolarized beam of light passing through a polarizer is one half of the value of the original intensity.

Question 12

Electromagnetic waves are a result of a stationary electric field and a changing magnetic field.

Question 13

The electric energy density in an electromagnetic wave is higher than its magnetic energy density.

Question 14

Electromagnetic waves do not require a medium to be transmitted.

Question 15

Electromagnetic waves are

A) transverse.
B) longitudinal.
C) longitudinal and transverse.
D) None of the other answers given is correct.

Question 16

The Doppler effect is observed when the source and the observer are at rest with respect to each other.

Question 17

Accelerated charges radiate electromagnetic waves.

Question 18

Electromagnetic waves transmit electromagnetic energy.

Question 19

An electromagnetic wave is a result of electric and magnetic fields acting together.

Question 20

The ratio of the electric field to the magnetic field in the electromagnetic wave is the speed of the light.

Question 21

The energy density of an electromagnetic wave is

A) entirely in the electric field.
B) entirely in the magnetic field.
C) 1/4 in the electric field and 3/4 in the magnetic field.
D) 1/4 in the magnetic field and 3/4 in the electric field.
E) equally divided between the magnetic and the electric fields.

Question 22

FIGURE 25-1
An electromagnetic wave propagates along the +y direction as shown in Figure 25-1. If the E-field at the origin is along the +z direction, what is the direction of the B-field?

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

Question 23

Object A in the shape of a disk of radius r is placed a distance R away from an intense light source. Object B, made from the same material as object A, is in the shape of a disk of radius 2r and placed a distance 2R away from the same light source. We observe which of the following?

A) Both objects experience the same amount of radiation pressure but receive different amounts of linear momentum.
B) The objects experience different amounts of radiation pressure and receive different amounts of linear momentum.
C) Both objects experience the same amount of radiation pressure and the same amount of linear momentum.
D) The objects experience different amounts of radiation pressure but receive the same amount of linear momentum.

Question 24

Which one of the following is the correct representation of the electromagnetic waves from longer wavelength to shorter wavelength?

A) radio waves, infrared, microwaves, UV, visible, X-rays, gamma rays
B) radio waves, UV, X-rays, microwaves, infrared, visible, gamma rays
C) radio waves, microwaves, visible, X-rays, infrared, UV, gamma rays
D) radio waves, microwaves, infrared, visible, UV, X-rays, gamma rays
E) radio waves, infrared, X-rays, microwaves, UV, visible, gamma rays

Question 25

The right hand rule for the direction of propagation of the electromagnetic waves is to

A) point the forefinger of your right hand toward E vector, middle finger toward the B vector, and the thumb will represent the propagation.
B) point the middle finger toward the E vector, the forefinger toward the B vector, and the thumb will represent the direction of propagation.
C) point the fingers of your right hand toward the E vector, curl your fingers towards the B vector, and the thumb will point the direction of propagation.
D) point the fingers of your left hand toward the E vector, curl your fingers towards the B vector, and the thumb will point the direction of propagation.
E) None of the other answers is correct.

Question 26

The first scientific attempt to measure the speed of light was made by

A) Galileo.
B) Faraday.
C) Maxwell.
D) Newton.
E) Romer.

Question 27

Which one of the following is the correct order of the electromagnetic spectrum from low to high frequencies?

A) radio waves, infrared, microwaves, UV, visible, X-rays, gamma rays
B) radio waves, UV, X-rays, microwaves, infrared, visible, gamma rays
C) radio waves, microwaves, infrared, visible, UV, X-rays, gamma rays
D) radio waves, microwaves, visible, X-rays, infrared, UV, gamma rays
E) radio waves, infrared, X-rays, microwaves, UV, visible, gamma rays

Question 28

The transverse nature of electromagnetic waves is apparent because

A) they are electric in nature.
B) they are magnetic in nature.
C) they can be polarized.
D) they are electromagnetic in nature.
E) None of the previous answers is correct.

Question 29

In 1676 Romer announced what value for the speed of light?

A) 2.55 × 10⁸ m/s
B) 2.99 × 10⁸ m/s
C) 1.99 × 10⁸ m/s
D) 3.13 × 10⁸ m/s
E) 2.25 × 10⁸ m/s

Question 30

Which one of the following is not an electromagnetic wave?

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

Question 31

FIGURE 25-2
For an xyz-coordinate system shown in Figure 25-2, if the E-vector is in the +z direction, and the B-vector is in the +x direction, what is the direction of propagation of the electromagnetic waves?

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

Question 32

The direction of propagation of electromagnetic waves is given by the

A) right hand rule.
B) left hand rule.
C) right and left hand rules.
D) None of the other answers given is correct.

Question 33

Which of the following expressions is the correct representation for the speed of light?

A)
B)
C)
D) 1/
E) 3/

Question 34

Electromagnetic waves can be produced by

A) electric charges moving with constant velocity.
B) electric charges at rest.
C) electric charges in accelerated motion.
D) All of the previous answers are correct.
E) None of the previous answers is correct.

Question 35

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

A) Horizontal and pointing south
B) Vertical and pointing down
C) Horizontal and pointing north
D) Vertical and pointing up
E) Horizontal and pointing east

Question 36

A particle of interplanetary dust is close to the Sun and interacts with the Sun's gravitational field as well as with the light emitted by the Sun. If it only interacts appreciably with the Sun, can it be pushed away from the Sun instead of being pulled towards it?

A) No, the gravitational force will always dominate if the object is large enough.
B) No, the gravitational force will always dominate if the object is close enough.
C) Yes, if the object is small enough, radiation pressure will win over.
D) Yes, but the object must be very large so that it can gain enough radiation pressure.
E) None of the previous answers is correct.

Question 37

Which one of the following is the correct representation of the relationship between the speed of a wave (v), frequency of the wave (f), and its wavelength (λ)?

A) v = 2λ
B) v = 2f
C) v = λ/f
D) v = fλ
E) v = f/λ

Question 38

A distance R away from a light source we observe which of the following for the electromagnetic field it produces?

A) Both the light intensity and the magnitude of the electric field drop as 1/R₂.
B) The light intensity drops as 1/R₂, but the magnitude of the electric field drops as 1/R.
C) Both the light intensity and the magnitude of the electric field drop as 1/R.
D) The light intensity drops as 1/R, but the magnitude of the electric field drops as 1/R₂.
E) None of the previous answers is correct.

Question 39

Two objects are in all respects identical except for the fact that one was coated with a substance that is an excellent reflector of light while the other was coated with a substance that is a perfect absorber of light. You place both objects at the same distance from a powerful light source so they both receive the same amount of energy U from the light. The linear momentum these objects will receive is such that:

A) The reflecting objects receives a larger amount of momentum.
B) Both objects receive the same amount of momentum.
C) The reflecting object receives a smaller amount of momentum.
D) None of the previous answers is correct.

Question 40

Which of the following expressions is correct for the transmitted intensity of an unpolarized beam of light with an intensity I_i passing through a polarizer?

A) I_t = I_i
B) I_t = (1/2) I_i
C) I_t = (1/4) I_i
D) I_t = 2 I_i
E) I_t = 4 I_i

Question 41

A radio station broadcasts at a frequency of 80 MHz. How far will this signal travel in 67 ms?

A) 60 × 10⁶ m
B) 67 m
C) 40 × 10⁶ m
D) 80 m
E) 20 × 10⁶ m

Question 42

Unpolarized light of intensity I_o passed through a Polaroid sheet with its polarizing axis at the 12 o'clock position and then through a second with its polarizing axis at the 1 o'clock position. What is the intensity of the emerging light?

Question 43

A car is going past a radio station at a speed of 40.0 m/s. If the radio station broadcasts at a frequency of 74.5 MHz, what change in frequency does the driver observe?

A) 9.93 Hz
B) 99.3 Hz
C) 993 Hz
D) 7.45 Hz
E) 74.5 Hz

Question 44

The intensity of solar radiation near the earth is 1.4 × 10³ W/m². What force is exerted by solar radiation impinging normally on a 5.0 m² perfectly reflecting panel of an artificial satellite orbiting the earth?

Question 45

In Fizeau's experiment to measure the speed of light, the wheel has 475 notches and rotates with a speed of 40.0 rev/sec. Light passing through one notch travels to the mirror and back just in time to pass through the next notch. If the distance between the wheel and the mirror is 7890 m, what is the speed of light measured by this experiment?

A) 3.00 × 10⁸ m/s
B) 3.00 × 10^-8 m/s
C) 3.22 × 10⁸ m/s
D) 3.22 × 10^-8 m/s
E) 2.25 × 10⁸ m/s

Question 46

A radio station broadcasts at 80 MHz. How long does it take for this radio signal to travel a distance of 20 × 10⁶ m?

A) 0.15 × 10^-2 s
B) 15 ms
C) 6.7 × 10^-2 s
D) 20 ms
E) 25 ms

Question 47

An FM radio station broadcasts at 96.7 MHz. What is the wavelength associated with this broadcast?

Question 48

In Fizeau's experiment to measure the speed of light, the wheel has 475 notches and rotates with a speed of 55.0 rev/sec. Light passing through one notch travels to the mirror and back just in time to pass through the next notch. If the distance between the wheel and the mirror is 8800 m, how much time does it take the wheel to rotate from one notch to the next?

A) 11.9 s
B) 24.8 s
C) 3.83 × 10^-5 s
D) 7.44 × 10^-5 s
E) 8.44 × 10^-5 s

Question 49

A beam of light travels a distance of 2900 m. How much time does it take?

A) 9.7 s
B) 9.7 ms
C) 9.7 μs
D) 9.7 ns
E) 9.7 ps

Question 50

How far does a beam of light travel in one full year?

A) 80 × 10¹² m
B) 95 × 10¹⁴ m
C) 30 × 10⁸ m
D) 20 × 10¹⁵ m
E) 36 × 10¹⁶ m

Question 51

A car is approaching a radio station at a speed of 25.0 m/s. If the radio station broadcasts at a frequency of 74.5 MHz, what change in frequency does the driver observe?

A) 98.3 Hz
B) 6.21 Hz
C) 726 Hz
D) 67.0 Hz
E) 64.5 Hz

Question 52

What is the distance traveled by a beam of light in a time of 2.0 ms?

A) 6.0 × 10⁵ m
B) 0.66 × 10⁵ m
C) 90 m
D) 70 m
E) 60 m

Question 53

A laser beam takes 24 ms to be reflected from the surface of a planet. How far from the laser source is this planet's surface?

A) 24 × 10⁵ m
B) 12 × 10⁵ m
C) 18 × 10⁵ m
D) 36 × 10⁵ m
E) 48 × 10⁵ m

Question 54

The frequency of a microwave signal is 9.76 GHz. What is its wavelength in meters?

A) 3.07 × 10^-2 m
B) 2.07 × 10^-2 m
C) 1.07 × 10^-2 m
D) 5.07 × 10^-2 m
E) 4.07 × 10^-2 m

Question 55

The distance between the two planets is 1.6 × 10⁶ m. How much time would the light signal take to go from one planet to the other?

A) 1.9 × 10^-2 s
B) 0.45 × 10^-2 s
C) 0.53 × 10^-2 s
D) 1.3 × 10^-2 s
E) None of the other answers is correct.

Question 56

The total electromagnetic power emitted by the Sun is 3.8 ×10²⁶ W. What is the radiation pressure near the orbit of Mercury, which has an orbital radius of 5.8 × 10¹⁰ m?

Question 57

In Fizeau's experiment for measuring the speed of light, the wheel has 475 notches. What rotational speed is required for the return beam of light to pass through the next notch? The time between successive notches is 6.65 × 10^-5 s.

A) 20.4 rev/sec
B) 16.6 rev/sec
C) 31.7 rev/sec
D) 66.4 rev/sec
E) 90.9 rev/sec

Question 58

A Doppler weather radar operates at a frequency of 3.40 GHz. The wave from this radar system reflects from an approaching weather system moving with a speed of 39.0 m/s. What is the difference in frequency between the outgoing and returning waves?

A) 442 Hz
B) 351 Hz
C) 419 Hz
D) 322 Hz
E) 670 Hz

Question 59

A cordless phone operates at 900 MHz. What is the associated wavelength?

Question 60

Unpolarized light of intensity I passes through four Polaroid sheets whose polarizing angles are rotated 30° from each other so that the last sheet is aligned at 90° to the first. What is the intensity of the light emerging from the fourth sheet?

Question 61

A 60.0 W light bulb radiates light uniformly in all different directions. What is the value of E at a distance of 0.400 m from the bulb?

A) 162 N/C
B) 212 N/C
C) 82.1 N/C
D) 106 N/C
E) 52.9 N/C

Question 62

The wavelength of an electromagnetic wave is 600 nm. What is its frequency?

A) 200 × 10¹² Hz
B) 300 × 10¹² Hz
C) 400 × 10¹² Hz
D) 500 × 10¹² Hz
E) 600 × 10¹² Hz

Question 63

A certain part of the electromagnetic spectrum ranges from 200 nm to 400 nm. What is the lowest frequency associated with this portion of the spectrum?

A) 1.50 × 10¹⁴ Hz
B) 7.50 × 10¹³ Hz
C) 7.50 × 10¹⁴ Hz
D) 7.50 × 10¹⁵ Hz
E) 1.50 × 10¹⁵ Hz

Question 64

The average intensity of the sunlight in Miami, Florida, is 1060 W/m². What is the average value of the force exerted on a 16m² surface that absorbs this light?

A) 7.83 × 10^-5 N
B) 1.63 × 10^-5 N/m²
C) 2.61 × 10^-5 N
D) 5.65 × 10^-5 N
E) 0.204 × 10^-5 N

Question 65

The value of the magnetic field for a certain type of electromagnetic wave is 2.12 μT. What is the value of the electric field for that wave?

A) 636 V/m
B) 636 N/C
C) 636 J/Cm
D) All of the answers given are correct.
E) None of the answers given is correct.

Question 66

A 60.0-W light bulb radiates light uniformly in all different directions. What is the value of B at a distance of 0.700 m from the bulb?

A) 1.76 × 10^-7 T
B) 2.02 × 10^-7 T
C) 2.22 × 10^-7 T
D) 4.86 × 10^-7 T
E) None of the other answers is correct.

Question 67

A 60.0 W light bulb radiates light uniformly in all different directions. What is the average intensity of the light bulb at a distance of 0.400 m from the bulb?

A) 14.9 W/m²
B) 37.2 W/m²
C) 27.4 W/m²
D) 11.9 W/m²
E) 29.8 W/m²

Question 68

A certain part of the electromagnetic spectrum ranges from 200 nm to 400 nm. What is the highest frequency associated with this portion of the spectrum?

A) 1.50 × 10¹⁴ Hz
B) 7.50 × 10¹³ Hz
C) 7.50 × 10¹⁴ Hz
D) 7.50 × 10¹⁵ Hz
E) 1.50 × 10¹⁵ Hz

Question 69

An 8.000-mW laser beam emits a cylindrical beam of light 0.9000 mm in diameter. What is the rms value of the electric field in this beam?

A) 2176 N/C
B) 1000 N/C
C) 1088 N/C
D) 4122 N/C
E) 2000 N/C

Question 70

The magnetic field component of the electromagnetic wave is 15.0 μT. What is the magnetic energy density of the wave?

A) 2.26 × 10^-4 J/m³
B) 8.95 × 10^-5 J/m²
C) 1.79 × 10^-4 J/m³
D) 4.47 × 10^-4 J/m²
E) 9.72 × 10^-5 J/m³

Question 71

The maximum value of the magnetic field component of an electromagnetic wave is 2.81 μT. What is the rms value of the magnetic field?

A) 2.81 μT
B) 2.46 μT
C) 3.12 μT
D) 3.97 μT
E) 1.99 μT

Question 72

The average electric energy density of an electromagnetic wave is 0.600 × 10^-7 J/m³. What is the electric field component of this wave?

A) 116 J/Cm
B) 116 N/C
C) 116 V/m
D) All of the answers given are correct.
E) None of the answers given is correct.

Question 73

The wavelength of a certain portion of microwaves is 40 mm. What is its frequency?

A) 40 GHz
B) 4.0 GHz
C) 0.75 GHz
D) 75 GHz
E) 7.5 GHz

Question 74

An 8.000-mW laser beam emits a cylindrical beam of light 0.6000 mm in diameter. What is the maximum value of the magnetic field?

A) 9.240 × 10^-6 T
B) 17.22 × 10^-6 T
C) 12.42 × 10^-6 T
D) 20.50 × 10^-6 T
E) 15.40 × 10^-6 T

Question 75

Which of the following represents the maximum value of the magnetic field at a distance of 2.5 m from a 100 W light bulb?

A) 0.10 μT
B) 0.40 μT
C) 0.50 μT
D) 0.60 μT
E) 0.80 μT

Question 76

The rms value of the electric field component of an electromagnetic wave is 27.2 N/C. What is the maximum value of the electric field?

A) 38.5 N/C
B) 19.2 N/C
C) 27.2 N/C
D) 47.4 N/C
E) 52.8 N/C

Question 77

The average magnetic energy density of an electromagnetic wave is 8.95 × 10^-5 J/m³. What is the magnetic field component of this wave?

A) 12.0 μT
B) 13.0 μT
C) 14.0 μT
D) 15.0 μT
E) 16.0 μT

Question 78

The average intensity of the sunlight in Miami, Florida, is 1040 W/m². What is the average value of the radiation pressure due to this sunlight in Miami?

A) 2.28 × 10^-6 N/m²
B) 1.63 × 10^-6 N/m²
C) 7.83 × 10^-6 N
D) 3.46 × 10^-6 N/m²
E) 9.78 × 10^-6 N/m²

Question 79

The maximum value of the electric field in an electromagnetic wave is 2.0 V/m. What is the maximum value of the magnetic field?

A) 6.7 pT
B) 6.7 mT
C) 6.7 nT
D) 6.7 μT
E) 6.7 T

Question 80

The value of the electric field for a certain type of electromagnetic wave is 570 N/C. What is the value of the magnetic field for that wave?

A) 2.91 × 10^-6 T
B) 1.90 × 10^-6 T
C) 1.10 × 10^-6 T
D) 1.41 × 10^-6 T
E) 2.41 × 10^-6 T