Deck 22: Electromagnetic Waves

Question 1

The electromagnetic spectrum arranged by increasing wavelength is

A) radio waves,gamma rays,x-rays,visible light,infrared,microwave,ultra violet.
B) x-rays,gamma rays,ultraviolet,visible light,infrared,microwave,radio waves.
C) infrared,gamma rays,x-rays,ultraviolet,visible light,microwave,radio waves.
D) gamma rays,x-rays,ultraviolet,visible light,infrared,microwave,radio waves.

Answer 1

gamma rays,x-rays,ultraviolet,visible light,infrared,microwave,radio waves.

Question 2

An electromagnetic wave with a wave length about the same as the diameter of an apple would be

A) x-ray.
B) UV.
C) infrared.
D) microwave.
E) radio wave.

Answer 2

microwave.

Question 3

Light of 10 cm wavelength is classified as what type of radiation?

A) $\gamma$ -ray
B) x-ray
C) UV
D) microwave
E) visible

Answer 3

microwave

Question 4

The highest frequency in visible light is associated with the color

A) red.
B) orange.
C) green.
D) blue.
E) violet.

Question 5

1 THz = ?

A) 10³ Hz
B) 10⁶ Hz
C) 10⁹ Hz
D) 10¹² Hz
E) 10¹⁵ Hz

Question 6

Radio waves were discovered by

A) Hertz.
B) Maxwell.
C) Penzias.
D) Dumont.
E) Marconi.

Question 7

The wavelengths associated with thermal radiation at everyday temperatures are in the ________ spectral region.

A) infrared
B) ultraviolet
C) shorter visual
D) longer visual
E) x-ray

Question 8

A dipole radio transmitter has its rod shaped antenna oriented vertically.At a point due south of the transmitter,the radio waves have their magnetic field

A) oriented in a horizontal direction.
B) oriented east-west.
C) oriented vertically.
D) oriented north-south.

Question 9

Electromagnetic waves of wavelength 1000 nm are classified as

A) radio waves.
B) microwaves.
C) infrared.
D) x-rays.
E) gamma rays.

Question 10

An electromagnetic wave is created by

A) an electrical charge moving at a certain velocity.
B) all electric charges.
C) a magnetic moving with a certain velocity.
D) an accelerating electric charge.

Question 11

Wavelengths just shorter than visible light are classified as

A) gamma rays.
B) x-rays.
C) microwaves.
D) ultraviolet.
E) radio waves.

Question 12

What is a light-year in SI units?

A) 3.0 $\times$ 10¹⁵ m
B) 9.5 $\times$ 10¹⁵ m
C) 3.0 $\times$ 10¹¹ m
D) 1.1 $\times$ 10¹¹ m
E) 4.5 $\times$ 10³⁷ m

Question 13

Electromagnetic wavelengths of a few centimeters are classified as in what range?

A) visible
B) ultraviolet
C) microwave
D) radio
E) gamma ray

Question 14

Your favorite radio station is located due north of your house and broadcasts using a horizontal electric dipole antenna directed north-south.To receive this signal you need to

A) move to a town that is farther to the east or west.
B) use a magnetic dipole antenna instead of an electric dipole antenna.
C) orient the receiving antenna horizontally north-south.
D) use a vertical receiving antenna.

Question 15

Light of wavelength 600 nm in air goes into a medium where the index of refraction is 1.73.What is the frequency of this light in the medium?

A) 5.00 $\times$ 10¹⁴ Hz
B) 2.89 $\times$ 10¹⁴ Hz
C) 8.65 $\times$ 10¹⁴ Hz
D) 3.46 $\times$ 10¹⁴ Hz
E) 1.04 $\times$ 10¹⁴ Hz

Question 16

In what spectral range are black lights that cause materials to fluoresce in the visible?

A) x-ray
B) infrared
C) ultraviolet
D) radio
E) microwave

Question 17

The background radiation in space corresponds to what temperature blackbody radiation?

A) 0 K
B) 2.7 K
C) 273 K
D) 5800 K
E) 98.6 $^{\circ}$ F

Question 18

$\varepsilon$ _o $\mu$ _o = ?

A) c
B) c²
C) c^-1
D) c^-2
E) c^½

Question 19

How long does it take for a radio signal to travel to a spacecraft 1.5 $\times$ 10¹¹ m away?

A) 5.0 s
B) 50 s
C) 5.0 $\times$ 10² s
D) 5.0 $\times$ 10³ s
E) 1.0 $\times$ 10³ s

Question 20

The longest wavelengths of visible light are in the color

A) red.
B) orange.
C) green.
D) blue.
E) violet.

Question 21

At a distance of 10 m from a light bulb the rms value of the electric field is 16 V/m.What is the rms value of the electric field at a distance of 20 m from the light bulb?

A) 32 V/m
B) 16 V/m
C) 8.0 V/m
D) 4.0 V/m
E) 2.0 V/m

Question 22

Which of the following is the direction of an electromagnetic wave having electric and magnetic vectors E and B?

A) E
B) B
C) E·B
D) E $\times$ B
E) B $\times$ E

Question 23

In vacuum,the components of an EM wave are E_y = 50( V/m ) cos [(5.00 m^-1)x + $\omega$ t], E_x = 0, and E_z = 0.In what direction is this wave moving?

A) positive x-direction
B) negative x-direction
C) positive y-direction
D) negative y-direction
E) positive or negative z-direction

Question 24

Light passes from medium one ( v₁ ) to medium two ( v₂ ). If v₁ < v₂ then at the boundary

A) f increases , $\lambda$ decreases.
B) f does not change, $\lambda$ increases.
C) f decreases, $\lambda$ increases.
D) f does not change, $\lambda$ decreases.

Question 25

In vacuum,the components of an EM wave are E_y = 50( V/m )cos[(5.00 m^-1)x + $\omega$ t], E_x = 0, and E_z = 0.What is the wavelength of the wave?

A) 5.00 m
B) 0.200 m
C) 1.26 m
D) 2.52 m
E) 0.796 m

Question 26

Approximately how long does it take for light to travel one foot?

A) 1 ms
B) 1 $\mu$ s
C) 1 ns
D) 1 ps
E) 1 fs

Question 27

If the rms value of the electric field is 9.0 V/m at a distance of 6.0 m from an isotropic source,what is the rms value of the magnetic field at a distance of 12 m from the source?

A) 3.0 $\times$ 10^-8 T
B) 1.5 $\times$ 10^-8 T
C) 0.75 $\times$ 10^-8 T
D) 0.38 $\times$ 10^-8 T
E) 0.19 $\times$ 10^-8 T

Question 28

When light goes from one medium to another medium with a different index of refraction,which of the following do (does)NOT change?

A) the speed
B) the wavelength
C) the frequency
D) the speed and the wavelength
E) the frequency and the wavelength

Question 29

Household wiring can emit electromagnetic waves of frequency 60 Hz.What is the wavelength of these waves?

A) 5.0 $\times$ 10² m
B) 5.0 $\times$ 10³ m
C) 5.0 $\times$ 10⁴ m
D) 5.0 $\times$ 10⁵ m
E) 5.0 $\times$ 10⁶ m

Question 30

The sun is 150 $\times$ 10⁶ km from the Earth.How long does it take for light to travel this distance?

A) 5.00 $\times$ 10⁵ s
B) 5.00 $\times$ 10⁴ s
C) 5.00 $\times$ 10³ s
D) 5.00 $\times$ 10² s
E) 5.00 $\times$ 10¹ s

Question 31

If the wavelength of light is 400 nm in a substance where the speed of light is 2.35 $\times$ 10⁸ m/s,what is the wavelength of this light in air?

A) 313 nm
B) 400 nm
C) 511 nm
D) 635 nm
E) 940 nm

Question 32

If light has a wavelength of 600 nm in a vacuum,what is its wavelength in a material with an index of refraction of 1.50?

A) 600 nm
B) 900 nm
C) 400 nm
D) 1.35 $\times$ 10³ nm
E) 267 nm

Question 33

The speed of an electromagnetic wave in vacuum depends on

A) the amplitude of the electric and magnetic fields.
B) the frequency of the wavelength.
C) none of these choices are correct
D) the angle between the electric and magnetic fields.

Question 34

In vacuum,the components of an EM wave are E_y = 50( V/m )cos[(5.00 m^-1)x + $\omega$ t], E_x = 0, and E_z = 0.What is $\omega$ ?

A) 1.50 $\times$ 10⁹ rad/s
B) 1.20 $\times$ 10⁹ rad/s
C) 1.00 $\times$ 10⁹ rad/s
D) 8.00 $\times$ 10⁸ rad/s
E) More information is needed.

Question 35

In vacuum,the components of an EM wave are E_y = 50( V/m )cos[(5.0 m^-1)x + $\omega$ t], E_x = 0, and E_z = 0.What is the amplitude of the magnetic field for this wave?

A) 5.00 $\times$ 10^-7 T
B) 1.67 $\times$ 10^-7 T
C) 2.00 $\times$ 10^-7 T
D) 1.50 $\times$ 10^-6 T
E) 1.33 $\times$ 10^-6 T

Question 36

What is the wave number for a wavelength of 600 nm?

A) 600 nm
B) 1.67 $\times$ 10⁶ m^-1
C) 1.05 $\times$ 10⁷ m^-1
D) 9.55 $\times$ 10^-8 m
E) 9.55 $\times$ 10^-8 m^-1

Question 37

How far does light travel in a century?

A) 9.5 $\times$ 10²⁰ m
B) 9.5 $\times$ 10¹⁷ m
C) 9.5 $\times$ 10¹⁵ m
D) 9.5 $\times$ 10¹⁴ m
E) 9.5 $\times$ 10¹² m

Question 38

What is the wavelength from a radio station having frequency 107.7 MHz?

A) 2.790 m
B) 27.90 m
C) 32.30 m
D) 323.0 m
E) 108.0 m

Question 39

What index of refraction halves the wavelength that light has in a vacuum?

A) 1.33
B) 1.50
C) 1.41
D) 2.00
E) 5.00

Question 40

What is the speed of light in a material that has an index of refraction of 2.0?

A) 6.0 $\times$ 10⁸ m/s
B) 1.5 $\times$ 10⁸ m/s
C) 2.0 $\times$ 10⁸ m/s
D) 5.0 $\times$ 10⁸ m/s
E) No such index can exist.

Question 41

Unpolarized light of intensity I₀ is sent through 4 polarizers,each of the last three rotated 30 $^{\circ}$ from the previous polarizer so that the last polarizer is perpendicular to the first.What is the intensity transmitted by this system?

A) 0.75 I₀
B) 0.50 I₀
C) 0.42 I₀
D) 0.21 I₀
E) 0

Question 42

Randomly polarized light of intensity I₀ is passed through two polarizers whose transmission axes differ by 45 $^{\circ}$ .What is the intensity of the light that has passed through both polarizers?

A) 0.70 I₀
B) 0.50 I₀
C) 0.35 I₀
D) 0.25 I₀
E) 0.00

Question 43

If a 20 W laser beam,which has an initial diameter of 2.0 mm,spreads out to a diameter of 2.0 m after traveling 10,000 m,what is the initial E_rms of the beam?

A) 4.9 $\times$ 10⁴ V/m
B) 2.5 $\times$ 10³ V/m
C) 1.2 $\times$ 10³ V/m
D) 1.9 $\times$ 10² V/m
E) 1.7 $\times$ 10² V/m

Question 44

For electromagnetic radiation of intensity of 1.00 W/m²,what is the rms value of the electric field?

A) 19.4 V/m
B) 9.69 V/m
C) 6.45 $\times$ 10^-8 V/m
D) 9.11 $\times$ 10^-8 V/m
E) 3.00 $\times$ 10⁷ V/m

Question 45

Using the approximate formula for the Doppler shift, f₀ $\approx$ f_s (1 + v_rel / c) one finds that a source is moving away at 0.60 c.What result would the exact formula yield for the recession speed?

A) 0.84 c
B) 0.72 c
C) 0.60 c
D) 0.54 c
E) 0.40 c

Question 46

At the summer solstice in June,at what latitude is the sun directly overhead at solar noon?

A) 0.0 $^{\circ}$ (the equator)
B) 23.5 $^{\circ}$ N
C) 23.5 $^{\circ}$ S
D) 66.5 $^{\circ}$ N
E) 40.0 $^{\circ}$ N

Question 47

If the intensity of radiation from the sun is 1.4 kW/m² at a distance of 150 $\times$ 10⁶ km,at what distance is the intensity 5.6 kW/m²?

A) 300 $\times$ 10⁶ km
B) 100 $\times$ 10⁶ km
C) 75 $\times$ 10⁶ km
D) 38 $\times$ 10⁶ km
E) less than 30 $\times$ 10⁶ km

Question 48

What is the intensity of the electromagnetic radiation at a distance of 2.00 m from a 100 W isotropic source?

A) 25.0 W/m²
B) 6.25 W/m²
C) 4.00 W/m²
D) 1.99 W/m²
E) 1.00 W/m²

Question 49

If a 20 W laser beam,which has an initial diameter of 2.0 mm,spreads out to a diameter of 2.0 m after traveling 10,000 m,what is the initial intensity of the beam?

A) 20 $\times$ 10⁶ W/m²
B) 6.4 $\times$ 10⁶ W/m²
C) 3.2 $\times$ 10⁶ W/m²
D) 2.0 $\times$ 10⁵ W/m²
E) 1.0 $\times$ 10⁵ W/m²

Question 50

Plane polarized light of intensity I₀ is sent through a polarizer rotated 45 $^{\circ}$ clockwise to the original plane of polarization and then through a second polarizer rotated 45 $^{\circ}$ counter-clockwise measured from the original plane of polarization.What is the transmitted intensity?

A) 0.71 I₀
B) 0.50 I₀
C) 0.35 I₀
D) 0.25 I₀
E) 0

Question 51

Light from an astronomical source is found to be shifted to a one percent lower frequency than had the source been at rest.What radial velocity could cause such a shift?

A) 3.0 $\times$ 10⁷ m/s moving away from the observer
B) 3.0 $\times$ 10⁶ m/s moving away from the observer
C) 3.0 $\times$ 10⁶ m/s moving toward the observer
D) 1.5 $\times$ 10⁶ m/s moving toward the observer
E) 1.5 $\times$ 10⁶ m/s moving away from the observer

Question 52

How fast would you have to drive in order to see a red light as green? Assume $\lambda$ = 630 nm for red and $\lambda$ = 530 nm for green

A) 5 $\times$ 10⁷ m/s
B) 5 $\times$ 10⁶ m/s
C) 5 $\times$ 10⁵ m/s
D) 5 $\times$ 10⁴ m/s

Question 53

Plane polarized light of intensity I₀ is passed through two polarizers,the first one at 45 $^{\circ}$ to the original plane of polarization and the second rotated an additional 45 $^{\circ}$ more so that it is perpendicular to the original plane of polarization.What intensity is transmitted?

A) 0.50 I₀
B) 0.35 I₀
C) 0.25 I₀
D) 0.13 I₀
E) 0

Question 54

If a 20 W laser beam,which has an initial diameter of 2.0 mm,spreads out to a diameter of 2.0 m after traveling 10,000 m,what is the final intensity of the beam?

A) 20 $\times$ 10^-4 W/m²
B) 20 $\times$ 10^-6 W/m²
C) 20 $\times$ 10^-8 W/m²
D) 6.4 W/m²
E) 6.4 $\times$ 10^-6 W/m²

Question 55

Plane polarized light of intensity I₀ is passed through a polarizer oriented at 45 $^{\circ}$ to the original plane of polarization.What is the intensity transmitted?

A) 0.70 I₀
B) 0.50 I₀
C) 0.35 I₀
D) 0.25 I₀
E) 0.00

Question 56

If you are facing north with the Sun directly overhead,the light coming to your eyes from the sky just above the horizon is

A) partially polarized east-west.
B) partially polarized north-south.
C) randomly polarized.
D) partially polarized up-down.

Question 57

Radiation of intensity 1.00 kW/m² is incident on an area perpendicular to the incoming light.The area is now rotated 20 $^{\circ}$ about an axis perpendicular to the incoming light.What is the resulting power per unit area now reaching the surface?

A) 1.00 kW/m²
B) 0.940 kW/m²
C) 0.880 kW/m²
D) 0.800 kW/m²
E) 0.340 kW/m²

Question 58

The light from a distant star is shifted such that the peak of its spectrum, at 620 nm ,is shifted to 635 nm.What is its radial velocity relative to Earth?

A) -0.11c
B) -0.024c
C) -0.15c
D) -0.012c

Question 59

Light of a wavelength of 661.1 nm is received from a star that is emitting light of a wavelength of 659.6 nm.How fast is the star moving relative to the earth and is it moving toward or away?

A) -580 km/s away
B) 580 km/s away
C) -680 km/s away
D) 680 km/s away

Question 60

If unpolarized light with E_rms = 20 V/m is passed through a polarizer,what is the transmitted E_rms?

A) 20 V/m
B) 14 V/m
C) 10 V/m
D) 7.1 V/m
E) 5.0 V/m

Question 61

The rms Electric field strength at a distance r from a 25 W light source is found to be 4.33 N/C.What is the distance r?

A) 22 m
B) 6.3 m
C) 30 m
D) 40 m

Question 62

Nexrad radar uses a frequency of 2.7 GHz to measure the speed of cloud systems.The radio waves from the transmitter are sent outward to the cloud system and reflected back,Doppler shifted.A Nexrad system observes clouds moving toward the transmitter at 21 m/s.What is the difference between the transmitted frequency and the frequency received after reflection off the cloud surface?

A) 380 Hz
B) 760 Hz
C) 570 Hz
D) 190 Hz

Question 63

For an unpolarized EM wave,the electric field direction is

A) perpendicular to the magnetic field direction.
B) parallel to the magnetic field direction.
C) perpendicular to the direction of wave propagation,but randomly oriented with respect to the magnetic field direction.
D) parallel to the direction of wave propagation.

Question 64

At the Earth's orbital distance,the intensity of the solar radiation is approximately 1400 W/m².What is the value for the intensity at Mercury's orbital distance,which is 38.7% the distance to the sun that the Earth is.

A) 2280 W/m²
B) 3800 W/m²
C) 9300 W/m²
D) 540 W/m²

Question 65

You wish to read from a single lightbulb in a lamp at your desk.In order to get the same brightness on the page from a 25 W bulb as you can from 100 W bulb,how much closer do you need to bring the lamp to your book? Assume that the light bulbs are equally efficient.

A) 1/2 the distance
B) 1/8 the distance
C) 1/4 the distance
D) 1/16 the distance

Question 66

A magnetic dipole antenna is set up due west of a radio installation that utilizes an electric dipole antenna as a transmitter.What should the orientation of the antenna be used?

A) east-west
B) horizontal
C) north-south
D) Unable to answer given the information.
E) vertical

Question 67

At the Earth's orbital distance,the intensity of the solar radiation is approximately 1400 W/m².What is the value for the rms Electric field strength in solar radiation?

A) 726 V/m
B) 363 kV/m
C) 527 kV/m
D) 513 kV/m

Question 68

The sun has a radius of 6.955 $\times$ 10⁸ km and a rotational period of 25.38 days.What is the difference is there in the peak of the observed spectrum between light received from the approaching side of the Sun and from the receding side of the sun? Observations from the middle of the sun place the spectral peak at 480 nm.

A) 13 nm
B) 6.4 nm
C) 1.6 nm
D) 3.2 nm

Question 69

At the Earth's surface,approximately 1000 W/m² is present due to solar radiation.At a latitude of 44.5 degrees North,the angle of the sun's rays,when the sun is highest in the sky on the winter solstice,are incident at an angle of 68 degrees from the vertical.What power is incident upon a 1.0 m $\times$ 1.5 m window in a vertical,south-facing wall at this time?

A) 1390 W
B) 930 W
C) 560 W
D) 370 W

Question 70

What power is produced by a light bulb that yields 12 mW on a 15 cm $\times$ 25 cm sheet of paper that is normal to the line directly toward the bulb,if the paper is 1.7 m from the bulb?

A) 2.9 W
B) 12 W
C) 1.7 W
D) 6.6 W

Question 71

The light from a distant star is that has a peak in its intensity spectrum at 620 nm and is moving at a rate of 0.024c towards Earth.What is the wavelength of the peak of its intensity spectrum,as observed on Earth?

A) 605 nm
B) 591 nm
C) 650 nm
D) 635 nm

Question 72

It is possible to detect Doppler shifts due to light on each side of a rapidly spinning star.Suppose it is seen that a nearby star,relatively stationary to us,is blueshifted in light on one side of the star and redshifted in the light from the other side.Suppose a star of radius 2.5 $\times$ 10⁸ km has light shifted from 525 nm to 527 nm on one side and to 523 nm on the other.What is the rotational period of the star?

A) 34 h
B) 32 h
C) 24 h
D) 16 h

Question 73

If the distance from a point source of EM radiation is doubled,the intensity is

A) doubled
B) the same as it was before.
C) reduced by a factor of four.
D) increased by a factor of four.
E) cut in half.