Deck 23: Electromagnetic Waves

Question 1

A radio wave transmits 4.8 W/m² average power per unit area. What is the peak value of the associated magnetic field? ( $\mu$ ₀ = 4 $\pi$ *10^-7 T.m/A and c = 3.00 * 10⁸ m/s)

A) 1.0 *10^-7 T
B) 8.4 *10^-3 T
C) 2.0 *10^-7 T
D) 30 T

Answer 1

2.0 *10^-7 T

Question 2

What is the maximum value of the electric field E at 0.50 m from a 100 W light bulb radiating in all directions? (µ₀ = 4 $\pi$ *10 ^{- 7} T.m/A, c = 3.00 *10⁸ m/s)

A) 3000 V/m
B) 155 V/m
C) 6000 V/m
D) 77 V/m

Answer 2

155 V/m

Question 3

In order of decreasing frequency, which of the following is correct?

A) infrared, visible, ultraviolet, and gamma
B) gamma, ultraviolet, visible, and infrared
C) visible, radio, ultraviolet, and X-ray
D) visible, gamma, ultraviolet, and X-ray

Answer 3

gamma, ultraviolet, visible, and infrared

Question 4

The Earth is 1.49 * 10¹¹ m from the Sun. If the solar radiation at the top of the Earth's atmosphere is 1340 W/m², what is the total power output of the Sun?

A) 2.34 * 10³⁰ W
B) 3.74 *10²⁶ W
C) 6.62 *10²⁶ W
D) 7.48 * 10²⁷ W

Question 5

An electromagnetic wave with a peak magnetic field component of 7.3 *10^-7 T has an associated peak electric field component of what value? ( $\mu$ ₀ = 4 $\pi$ *10^-7 T.m/A, $\varepsilon$ ₀ = 8.85* 10^-12 C²/N.m², and c = 3.00 * 10⁸ m/s)

A) 45 N/C
B) 2.0 *10^-5 N/C
C) 2.2 * 10² N/C
D) 0.50 *10^-15 N/C

Question 6

How is the direction of propagation of an electromagnetic wave oriented relative to the associated and fields?

A) parallel to , perpendicular to
B) parallel to , perpendicular to
C) parallel to both and
D) perpendicular to both and

Question 7

The electric field, , in an electromagnetic wave is oriented in what direction with respect to its associated magnetic field, ?

A) anti-parallel to
B) perpendicular to
C) at a 45° angle to
D) parallel to

Question 8

Peak values for a neodymium-glass laser are 1200 J for 1 nanosecond. If the cross section of the laser beam is 1 cm², what are the maximum values of E and B? (µ₀ = 4 $\pi$ *10^-7 T.m/A, c = 3.00 *10⁸ m/s)

A) 3 *10⁷ V/m, 2 T
B) 2 * 10⁸ V/m, 10 T
C) 1 *10¹⁰ V/m, 3 T
D) 3 * 10⁹ V/m, 10 T

Question 9

Maxwell guessed that visible light was an electromagnetic wave because of its:

A) energy.
B) frequency.
C) wavelength.
D) speed.

Question 10

A 100-kg spacecraft has a sail of area 300 that is absorbing sunlight of intensity . What is the resulting acceleration of the spacecraft?

A) 2.4
B)
C)
D)

Question 11

Maxwell developed his theory of electromagnetism by combining previous discoveries. He added his own original hypothesis that:

A) changing electric fields produce magnetic fields.
B) moving electric charges produce magnetic fields.
C) changing magnetic fields produce electric fields.
D) electric charges produce electric fields.

Question 12

A radar pulse returns 2.0 *10^-4 seconds after it is sent out, having been reflected by an object. What is the distance between the radar antenna and the object? (c = 3.00 *10⁸ m/s)

A) 3.0 *10⁴ m
B) 4.5 * 10⁴ m
C) 9.0 *10⁴ m
D) 6.0 * 10⁴ m

Question 13

A 6.0-J pulse of light from a laser has what momentum?

A) Light does not have momentum because it doesn't have mass.
B) 3.0 * 10⁹ kg·m/s
C) 6.7 * 10^-9 kg·m/s
D) 2.0 *10^-8 kg·m/s

Question 14

Determine the amount of energy carried in 50 m of a 3.5-mW He-Ne laser beam if the cross-sectional area of the beam is 5.0 *10^-6 m².

A) 2.9 * 10^-8 J
B) 5.8 *10^-10 J
C) 0.024 J
D) 2.9 * 10^-10 J

Question 15

An electromagnetic wave is made up of which of the following oscillating quantities?

A) magnetic fields only
B) electrons only
C) electric and magnetic fields
D) electric fields only

Question 16

Which one of the following scientists made the theoretical prediction that electromagnetic waves travel through a vacuum at the speed of light?

A) Hertz
B) Maxwell
C) Lenz
D) Faraday

Question 17

An electromagnetic wave with a peak electric field component of 7.5* 10² N/C has what associated peak magnetic field value? ( $\varepsilon$ ₀ = 8.85 *10^-12 C²/N.m², $\mu$ ₀ = 4 $\pi$ *10^-7 T.m/A, and c = 3.00 * 10⁸ m/s)

A) 2.8 *10^-11 T
B) 2.5 * 10^-6 T
C) 3.6 *10¹⁰ T
D) 4.0 *10^-7 T

Question 18

An electromagnetic wave with a peak magnetic field component of 3.2 *10 ^{- 7} T carries what average power per unit area? ( $\mu$ ₀ = 4 $\pi$ * 10^-7 T.m/A, $\varepsilon$ ₀ = 8.85 *10^-12 C²/N.m², and c = 3.00 * 10⁸ m/s)

A) 12 W/m²
B) 3.0 W/m²
C) 2.7 W/m²
D) 1.3 W/m²

Question 19

A solar cell has a light-gathering area of 10 cm² and produces 0.30 A at 0.80 V (DC) when illuminated with sunlight of intensity 1000 W/m². What is the efficiency of the solar cell?

A) 16%
B) 4%
C) 7%
D) 24%

Question 20

The intensity of light from the Sun is 1.3 kW/m² at the distance of the Earth. The Earth's radius is 6.4 * 10⁶ m. If all the sunlight that hits the Earth were absorbed, what would be the magnitude of the resulting force on the Earth?

A) 0.0087 N
B) 1.8 * 10⁸ N
C) 5.6 * 10⁸ N
D) 87 N

Question 21

A radar pulse sent out to an airplane at a distance of 20.0 km will return as an echo to the source in what time interval? (c = 3.00 * 10⁸ m/s)

A) 33.3 *10^-6 s
B) 133 *10^-6 s
C) 66.7 * 10^-6 s
D) 0.0333 *10^-6 s

Question 22

Which condition of motion must be met with regard to a charged particle if it is in the process of emitting electromagnetic radiation?

A) accelerates
B) moves at the speed of light
C) moves at constant velocity
D) moves parallel to a uniform magnetic field

Question 23

Temperature variation of different parts of a person's body can be detected by analyzing the emission pattern of which type of electromagnetic radiation?

A) microwave
B) infrared
C) x-rays
D) ultraviolet

Question 24

What value of inductance should be used in a series circuit with a capacitor of 9.0 *10^-4 $\mu$ F when designed to radiate a wavelength of 70 m? (c = 3.00 * 10⁸ m/s)

A) 3.8* 10^-4 mH
B) 1.9 *10^-4 mH
C) 3.8 mH
D) 1.5 *10 ^{- 3} mH

Question 25

An object that is giving off only infrared electromagnetic waves is giving off heat through:

A) radiation.
B) conduction.
C) convection.
D) visible light.

Question 26

Of the various types of electromagnetic radiation, the shortest wavelengths are the most penetrating through all forms of matter. Which of the following is it?

A) ultraviolet
B) gamma
C) infrared
D) visible light

Question 27

The electromagnetic radiation that causes tanning:

A) rarely passes through glass windows.
B) is absorbed by ozone.
C) can produce cancer.
D) is all of the above.

Question 28

The human eye is sensitive to light with wavelength up to 750 nm. What is the frequency of radiation at this wavelength? (1 nm = 10^-9 m and c = 3.00 * 10⁸ m/s)

A) 8.5 * 10⁸ Hz
B) 1.8 * 10⁸ Hz
C) 4.0 *10¹⁴ Hz
D) 7.7*10¹⁴ Hz

Question 29

A beam of polarized light of intensity I₀ passes through a sheet of ideal polarizing material. The polarization axis of the beam and the transmission axis of the sheet differ by 45°. What is the intensity of the emerging light?

A) 0.25I₀
B) 0.87I₀
C) 0.50I₀
D) 0.75I₀

Question 30

An ultraviolet light wave has a wavelength of 300 nm and speed of 1.8 * 10⁸ m/s through a transparent medium. What is the frequency of this wave in the medium? (1 nm = 10^-9 m and c = 3.00 * 10⁸ m/s)

A) 7.0 * 10¹⁴ Hz
B) 6.0 * 10¹⁴ Hz
C) 6.3 * 10² Hz
D) 10 * 10¹⁴ Hz

Question 31

When an electrical switch is closed or opened in the vicinity of an operating AM radio, a burst of static can be heard. Which of the following, involving the throwing of the switch, would likely be the cause for this static?

A) The sound from the switching is the source of waves.
B) Unnoticed lightning hits nearby every time the switch is thrown.
C) Static happens without any cause.
D) Electrons are accelerated during the switching process.

Question 32

Find the frequency of X-rays of wavelength 2 *10^-11 m. (c = 3*10⁸ m/s)

A) 3 * 10⁸ Hz
B) 1.5 * 10¹⁹ Hz
C) 3 * 10¹⁸ Hz
D) 6 *10⁹ Hz

Question 33

In order to keep its food hot, a restaurant will place it under which type of lamp?

A) ultraviolet
B) visible light
C) infrared
D) X-ray

Question 34

As an electromagnetic wave travels through free space, its speed can be increased by:

A) increasing its frequency.
B) increasing its energy only.
C) increasing both its energy and momentum.
D) None of the above will increase its speed.

Question 35

Polaroid sunglasses help when skiing on snow on a sunny day by reducing the sunlight from the snow. This light from the snow has been polarized by:

A) optical activity.
B) selective absorption.
C) reflection.
D) double refraction.

Question 36

A radio wave signal, which transmits at a frequency of 10.4 MHz, has what wavelength? (c = 3.00*10⁸ m/s)

A) 28.8 m
B) 2.4 *10^-2 m
C) 4.17 m
D) 41.7 m

Question 37

When the Sun is located near one of the horizons, an observer looking at the sky directly overhead will view partially polarized light. This effect is due to which of the following processes?

A) double refraction
B) optical activity
C) selective absorption
D) reflection

Question 38

Glass panes are opaque to a certain type of radiation, which can cause sunburn. What type of radiation is it? This radiation is important in ozone layer reactions.

A) gamma
B) ultraviolet
C) X-ray
D) microwave

Question 39

What is the wavelength of 200 MHz television EM waves? (c = 3 * 10⁸ m/s)

A) 9 km
B) 10 m
C) 1.5 m
D) 3 m

Question 40

Unpolarized light of intensity I₀ passes through two sheets of ideal polarizing material. If the transmitted intensity is 0.375I₀, what is the angle between the polarizers?

A) 22.5°
B) 60°
C) 30°
D) 45°

Question 41

Assume that Hubble's constant has the value . According to Hubble's law, how far away would a galaxy be if it were receding at 10% of the speed of light?

A)
B)
C)
D)

Question 42

An observer is moving in space toward a distant star at 200 km/s while the star is moving toward the observer at 400 km/s; the relative velocity being 600 km/s of approach. What relative change in frequency of the light from the star as seen by the observer? (The speed of light in space is 3.00 *10⁵ km/s).

A) 0.067% increase
B) 0.20% decrease
C) 0.20% increase
D) 0.033% decrease

Question 43

Why are sound waves not polarizable?

A) Because they are not electromagnetic.
B) They are not transverse.
C) They are not longitudinal.
D) But this is readily possible!

Question 44

Unpolarized light is passed through polarizer 1. The light then goes though polarizer 2 with its plane of polarization at 30.0° to that of polarizer 1. Polarizer 3 is placed after polarizer 2. Polarizer 3 has its plane of polarization at 30.0° to the plane of polarization of polarizer 2 and at 60.0° to that of polarizer 1. What fraction of the intensity of the original light gets though the last polarizer?

A) 0.707
B) 0.125
C) 0.281
D) 0.553

Question 45

Light not only has wavelike properties, but also has particle-like properties. What are these "particles" of light called?

A) quarks
B) wavicles
C) photons
D) etherons

Question 46

A beam of plane polarized light is incident on 3 polarizers, the first with an axis at 30° to the original plane of polarization, the second at 60° to the original plane of polarization, and the third at 30° to the original plane of polarization. What angle does the plane of polarization of the transmitted light make with the original plane of polarization of the original beam?

A) 30°
B) 180°
C) 90°
D) The answer is not given.

Question 47

Plane polarized light is sent through two consecutive polarizers, the first having its plane of polarization in the same direction as the incident light and the second having its plane at 90° to the original plane of polarization. A third polarizer, with plane of polarization at 60° to the original plane of polarization, is placed between the two other polarizers. What fraction of the original intensity now gets through?

A) 0.56
B) 0.19
C) 0
D) 0.25

Question 48

Star #1 is approaching the Earth with speed v. Star #2 is receding from the Earth with the same speed v. Measurements of the same spectral line from each of the stars show Doppler shifts in frequency. The light from which star will have the larger magnitude shift in frequency?

A) star #1
B) Both stars will have the same shift.
C) The value of the speed must be known before an answer can be found.
D) star #2

Question 49

Unpolarized light is passed through polarizer 1. The light then goes though polarizer 2 with its plane of polarization at 60.0° to that of polarizer 1. What fraction of the intensity of the original light gets though the second polarizer?

A) 0.125
B) 0.250
C) 0.707
D) 0.500

Question 50

The Doppler shift for electromagnetic radiation from distant galaxies moving toward the observer is called a:

A) vacuum shift.
B) blue shift.
C) red shift.
D) black shift.

Question 51

If the formula for the energy of a photon is , where h is a constant, c is the speed of light, and $\lambda$ is the wavelength of the photon, which of the following is the formula for the momentum of a photon?

A)
B)
C)
D)

Question 52

A material is optically active if it:

A) rotates the plane of polarization of the light passing through it.
B) exhibits interference.
C) absorbs light passing through it.
D) transmits all light passing through it.

Question 53

In the Doppler effect for electromagnetic waves, which of the following gives the greatest shift in frequency?

A) the source moving toward the non-moving observer at speed v
B) the observer moving toward the non-moving source at speed v
C) the source moving toward the approaching observer, both at speed v /2
D) All of the above give the same shift.