Radiation and Spectra Exam Questions Chapter 5

Astronomy by Fraknoi, Morrison, and Wolff

Multiple Choice Questions for Chapter 5:

Radiation and Spectra

by Andrew Fraknoi

NOTE: While the questions in this chapter are divided by section below, as usual, it should be noted that a number of the questions span more than one section, since the material itself is so inter-connected.

Section 5.1: The Behavior of Light

1. The scientist who worked out the mathematics of the connections between electricity, magnetism, and light in the 19th century was:

a. Albert Einstein

b. James Clerk Maxwell

c. Isaac Newton

d. Wilhelm Wien

e. Ludwig Boltzmann

2. Which of the following statements about the nucleus of a typical atom (such as a carbon atom in your little finger) is FALSE:

a. the nucleus has an overall positive charge

b. the nucleus takes up a very small amount of space compared to the entire atom

c. the nucleus contains both protons and neutrons

d. the nucleus repels the electrons which move around it

e. the nucleus contains most of the mass of the atom

3. In the 19th century, it became clear that magnetism was not a separate force, but was always produced by the action of

a. electric charges that were in motion

b. the gravitational pull of the Earth

c. the strong nuclear force acting on electrons

d. light moving through a vacuum

e. something possessed by all movie stars

4. Which of the following statements about electromagnetic radiation is FALSE?

a. it always spreads out at the speed of light

b. it is given off by all objects that are not at a temperature of absolute zero

c. it is typically produced when charged particles oscillate

d. different waves of electromagnetic radiation differ in their wavelength or frequency

e. the radiation consists of tiny charged particles given off by the nuclei of atoms

5. The light which allows you to see this very interesting exam is made up of waves. In these waves, the distance between crests is called the:

a. frequency

b. velocity

c. wavelength

d. amplitude

e. you can't fool me; in these waves, the distance between crests is zero

6. How fast do electro-magnetic waves travel?

a. at the speed of sound

b. at the speed of light

c. at the speed of charge

d. at different speeds, depending on the temperature of the atoms that produce them

e. they always have zero speed

7. We have two waves of light, A and B. Wave A has a higher frequency than wave B. Then wave B must have:

a. longer wavelength

b. higher speed

c. lower speed

d. shorter wavelength

e. this can’t be determined from the information given

8. This chapter discusses that light sometimes acts like a photon. What is a photon?

a. a charged particle in the nucleus of every atom

b. a kind of magnetic substance found in reflective minerals

c. a self-contained “packet” of electro-magnetic energy

d. a kind of sound that is too high frequency for the human ear to hear

e. you can’t fool me. Einstein showed that photons were a mistake – they don’t exist.

9. After a nice dinner around the campfire on a camping trip, you and a friend decide to get away from the fire to observe the stars. As you get farther and farther away, you see the brightness of the fire:

a. increase with distance

b. remain the same

c. decrease as the distance squared

d. change more and more in color (becoming redder)

e. this can't be answered without having more information

Section 5.2: The Electro-magnetic Spectrum

10. Consider a radio wave from the transmitter of your favorite radio station, which has just reached the antenna of the radio in your room. Which of the following statements about this radio wave is CORRECT?

a. it has a frequency very close to the highest possible frequency for electromagnetic waves

b. it traveled between the transmitter and your radio's antenna at the speed of sound

c. its wavelength is much longer than the wavelength of the light you see reflected from the page of this exam

d. the wave was originally produced by electrons that were not moving (at rest) inside the transmitter

e. the reason that it could reach your radio is because all of space is filled with a medium called the aether in which electromagnetic waves can vibrate

11. In the future, several students living on board a space station decide to have a race among different types of electromagnetic radiation. Which of the following travels through space the fastest?

a. visible light

b. radio waves

c. infrared

d. x-rays

e. you can't fool me, all of these travel through space at the same speed

12. The fastest speed in the universe is:

a. the speed of sound

b. the speed of light

c. the speed of electron oscillations

d. the speed with which Mercury orbits the Sun

e. the speed with which weekends seem to pass

13. Which of the following has the longest wavelength?

a. radio waves

b. visible light waves

c. ultraviolet waves

d. x-rays

e. you can't fool me, all these have the same wavelength

14. Which of the following has the highest frequency?

a. visible light

b. gamma rays

c. radio waves

d. ultraviolet waves

e. you can't fool me, all these have the same frequency

15. A Hertz is

a. a unit of wavelength

b. a unit of frequency

c. a unit of velocity

d. a unit of loudness

e. a well-known car-rental company

16. A fashion designer decides to bring out a new line of clothing which reflects the longest wavelength of visible light. What color will these articles of clothing be to the human eye?

a. yellow-green

b. blue

c. violet

d. red

e. black

17. Which of the following statements about photons is FALSE?

a. photons always travel at the speed of light

b. photons each carry a specific amount of energy

c. a photon of visible light cannot pass through the atmosphere of the Earth, and thus cannot be seen at the Earth's surface

d. high energy photons have a high frequency (when thought of as waves)

e. a gamma-ray photon carries more energy than a visible light photon

18. Not all wavelengths of electromagnetic radiation can penetrate the Earth's atmosphere. Of the following types of waves that come from space, which one are you likely to be able to detect most easily from our planet's surface:

a. x-rays

b. gamma rays

c. infrared waves

d. ultraviolet waves

e. radio waves of the wavelength that carry FM broadcasts

19. Most ultraviolet radiation does not penetrate to the Earth's surface. Instead it is absorbed in:

a. the ozone layer

b. the ionosphere

c. the region between the Earth and the Sun

d. stratosphere

e. tanning zone

20. One reason that human eyes evolved to detect visible light is:

a. it is the band of the electromagnetic spectrum with the lowest possible energy and thus easiest to detect

b. it is the only band of the spectrum that can travel through a vacuum

c. it is the band of the spectrum which is the least Doppler shifted coming from the Sun

d. it is a band of the spectrum where the Sun puts out a great deal of energy

e. it is the band of the spectrum where the warm Earth glows the most effectively at night

21. Which of the following statements about infrared radiation is TRUE?

a. it is the band of the electromagnetic spectrum where each wave or photon has the greatest energy

b. it was first discovered in 1800 in an experiment using sunlight and thermometers

c. unlike light, infrared can never travel as fast as the speed of light

d. while many stars give off infrared, there is nothing on Earth at the right temperature to emit it

e. it is the radiation responsible for giving sunburns (or in large doses, skin cancer)

22. Which of the following is not a type of electromagnetic wave with lower energy than visible light waves?

a. microwaves

b. radar waves

c. the waves that carry AM or FM broadcasts

d. the sound waves coming from your transistor radio

e. the waves that carry television transmissions

23. You are alone in a large, completely dark auditorium on Earth. What kind of telescope should I use from the other side of the auditorium to detect the electromagnetic radiation emitted by your body?

a. visible light

b. infra-red

c. ultra-violet

d. black light

e. no telescope will be effective if I am in a dark room

24. I want to examine the surface of a planet that is covered by a thick atmosphere (which includes oxygen and contains a very thick layer of water clouds that never clears). What wavelength of electromagnetic radiation would I be smartest to use:

a. visible light

b. x-rays

c. radar waves

d. ultra-violet

e. none would work

25. Of the following, which consists of electro-magnetic waves with the shortest wavelength?

a. a beam of green light

b. TV transmissions bringing us Monday night football

c. the sound of the instructor's voice

d. the waves of a dental x-ray

e. the rays that tan a sunbather on the beach

26. A politician who has just said something very dumb on an AM all-talk radio station suddenly remembers the astronomy class he had in college, and starts to worry that his words are now moving outward into space at the speed of light (and will embarrass him forever). Does he have a reason to worry?

a. Yes, because all radio waves do travel at the speed of light and all of them escape from the Earth

b. No, because radio waves travel much slower than the speed of light and will take a very long time to get anywhere

c. No, because radio waves are all absorbed by the ozone layer in the Earth's atmosphere

d. No, because AM radio waves are bounced back or scattered by the ionosphere and don’t get into space

e. Yes, because while all radio waves do not escape from the Earth, AM radio waves do

27. (In the absence of a strong magnetic field), what is the chief factor that determines what type of electromagnetic radiation objects give off:

a. their mass

b. their temperature

c. their distance from the Earth’s center

d. their chemical makeup

e. their size

28. The energy of random atomic and molecular motion is called

a. heat

b. the Doppler shift

c. spectroscopy

d. reflection

e. rock and roll

29. Which of the following has the greatest average energy of random atomic and molecular motion?

a. a cube of ice

b. a cube of water

c. a cube of steam

d. a cube of air (on Earth)

e. a cube of the Sun

30. An idealized object that does not reflect or scatter any radiation that hits it, but simply absorbs every bit of radiation that falls on it is called:

a. a Doppler surface

b. an electromagnetic radiator

c. a blackbody

d. a spectrum

e. a vice president

31. Two stars are giving off electromagnetic radiation. The hotter star will:

a. give off more radiation at all wavelengths

b. will have a higher average frequency of radiation

c. will radiate energy at more than one wavelength

d. will give off a continuous spectrum of waves

e. all of the above

32. An astronomer discovers a new star and wants to measure its temperature. She would typically do this by:

a. measuring the Doppler shift of its spectral lines

b. making a blackbody curve and finding the wavelength of the peak (maximum)

c. measuring the intensity of radio waves the star gives off

d. measuring how much light the star reflects

e. sending a graduate student with a very long (and durable) thermometer to the star's vicinity

33. An astronomer observes two ordinary stars. The first one turns out to be twice as hot as the second. This means that the first one radiates:

a. twice as much energy as the second

b. roughly the same amount of energy as the second

c. half as much energy as the second

d. about 16 times the energy of the second

e. this problem cannot be solved with just the information we were given

34. Wien’s Law relates the wavelength at which a star gives off the greatest amount of energy to the star’s

a. motion toward us or away from us

b. overall color

c. magnetic field

d. temperature

e. none of the above

35. The Stefan-Boltzmann Law relates the energy flux coming from a blackbody (such as a star) to its:

a. overall color

b. temperature

c. wavelength where maximum energy is emitted

d. atomic ground state

e. none of the above

36. Two stars have the same diameter and are at the same distance from us (but in different parts of the sky.) Star A has a temperature of 4000 K, while star B has a temperature of 8000K. Which of the following statements is true:

a. the two stars have the same total energy flux (luminosity)

b. star B has twice the energy flux (luminosity) that star A has

c. star B has one half the energy flux (luminosity) that star A has

d. star B has 16 times the energy flux (luminosity) that star A has

e. Sorry, professor, we don’t have enough information to compare the energy flux (luminosity) of the two stars

Section 5.3: Spectroscopy in Astronomy

37. When white light passes from the air into a different medium such as glass, it:

a. is dispersed into different colors

b. is reflected backwards

c. is refracted (bent)

d. is Doppler shifted

e. more than one of the above

38. Why is an absorption spectrum especially useful for astronomers?

a. It has dark lines in it that allow astronomers to determine what elements are in the star

b. It has bright lines in it which allow astronomers to determine how bright the star is

c. It helped astronomers to understand the rainbows we see on Earth after storms

d. It shows that the stars are transparent; we can see right through them

e. An absorption spectrum is not useful to astronomers at all. When they see one, it means they cannot learn anything about the stars that produced the annoying absorption.

39. An artist who likes working with sources of light decides to make a modern sculpture out of electrified glass tubes that contain very thin (rarified) neon gas. When the sculpture is finished, and the electricity is turned on, the tubes glow with a rich red color. What we are seeing is:

a. a continuous spectrum

b. an absorption spectrum

c. an emission spectrum

d. a Doppler shift

e. all of the above

40. Astronomers observe a typical star using a telescope and a spectrometer. They will see:

a. a continuous spectrum

b. an absorption spectrum

c. an emission spectrum

d. a Doppler shift

e. more than one of the above

41. One of the great triumphs of spectroscopy was when astronomers identified a new element in the Sun (one that was only later found on Earth). Today, this element is called:

a. Solarium

b. Hydrogen

c. Einsteinium

d. Helium

e. Astronomium

Section 5.4: The Structure of the Atom

42. If I were to scale up an atom until it were the size of a sports arena, the space filled by the positive charges inside the atom (according to the work of Ernest Rutherford early in this century) would be:

a. as big as the entire stadium (and very thinly spread out)

b. as big as the space filled by all the negative charges (that's why the atom is neutral)

c. very small (perhaps the size of a soccer ball) and in the middle

d. an extremely thin layer spread completely around the outer walls of the stadium

e. this question cannot be answered (even roughly) without knowing how many electrons the atom has

43. Atoms typically consist of electrons, protons, and neutrons. The most common isotope of one element, however, only has two of these three types of particles. This element is:

a. helium

b. hydrogen

c. uranium

d. carbon

e. silicon

44. Two versions of an element with different numbers of neutrons are called:

a. molecules

b. electron pairs

c. isotopes

d. ions

e. re-runs

45. In 1911 Ernest Rutherford did a famous experiment using fast-moving alpha particles as bullets and very thin gold foil as a target. The results of this experiment showed that:

a. the negative and positive charges were all spread out throughout the volume of each atom

b. that the absorption spectrum of gold atoms had more lines than scientists could explain

c. that alpha particles were neutral (demonstrating the existence of neutrons)

d. that the nucleus of an atom was tiny compared to the size of the whole atom

e. it was far better to use cheaper materials than gold for physics experiments

46. As of the time our textbook went to press, 118 different elements had been discovered. All of the ones with atomic number over 92 have been made in physics laboratories. When element 119 (one that has not yet been identified) is found, provided it is like the other artificially made elements, it will:

a. have only protons, no neutrons at all

b. soon be used in industry to make new kinds of plastics

c. have one of the smallest nuclei known

d. only remain stable for an extremely small fraction of a second

e. eventually be found in the Sun (with very high quality spectrometers)

47. The idea that atoms radiate energy only when their electrons move from higher to lower energy levels was first advanced by:

a. J. J. Thomson

b. Niels Bohr

c. Ernest Rutherford

d. Albert Einstein

e. Christian Doppler

48. Why do different types of atoms (elements) give off or absorb different spectral lines?

a. all elements have the same lines, but they are Doppler shifted by different amounts

b. in some elements, electrons can only move to odd numbered levels, in others only to even numbered ones

c. in heavier elements, diffraction spreads out the lines that the atom produces, making the colors different

d. because the spacing of the energy levels is different in different atoms

e. because some atoms do not have a ground state, while others have three or four

49. When an atom has lost one or more electrons, it is said to be:

a. ionized

b. excited

c. in its ground state

d. red shifted

e. over the hill

50. What happens as an electron falls from a higher level to a lower level in an atom?

a. a photon is given off

b. the color of the wave involved shifts to the red

c. a photon is absorbed

d. another electron from the lower level takes its place

e. nothing happens; electrons can only go from a lower level to a higher level

51. To go from a lower level in an atom to a higher level, an electron must

a. give off a photon of energy

b. lose its electric charge

c. absorb a photon of energy

d. wait until the atom has changed into another atom with more protons

e. get a permission slip from Niels Bohr

52. Planck's constant relates:

a. the energy of a wave to the number of protons in the nucleus of the atom that emitted it

b. the frequency of a wave to its energy (when thought of as a photon)

c. the maximum energy emitted by a blackbody to its temperature

d. the energy emitted by a star to its temperature

e. the Doppler shift of a light source to its speed

Section 5.5: Formation of Spectral Lines

53. How do astronomers learn what elements are present in a given star?

a. look at what color light dominates its continuous spectrum

b. listen for coded signals in the radio waves it gives off in the FM band

c. look at the absorption lines in its spectrum

d. send spacecraft like Voyager to examine its make-up from close-up

e. compare visible-light photographs of the star (taken with large telescopes) to those of the Sun.

54. The fact that each type of atom has a unique pattern of electron orbits helps explain why

a. some atoms don’t have any isotopes

b. each type of atom contains different numbers of neutrons

c. each type of atom shows different absorption or emission spectra

d. most atoms don’t have a ground state

e. astronomers have not been able to figure out what atoms stars are made of

55. The ground state in an atom is

a. the electron orbit with the lowest possible amount of energy

b. a place in the atom where the electric charge cancels out

c. the energy level from which it is most easy for an electron to escape

d. when the atoms has been ripped apart into the particles that made it up

e. the state an electron is in when it has absorbed three or more different photons

56. The Balmer Series of lines in the hydrogen atom was very important in the history of physics and astronomy. What made it so important?

a. It helped Rutherford explain the workings of the atomic nucleus

b. Balmer’s experiments with these lines helped prove Wien’s Law

c. When electrons change levels to produce the Balmer series, the emitted light is in the visible part of the spectrum, so the lines were easy to see with our eyes

d. The Balmer series of lines can only be observed from outer space; so the competition to see these lines led to the space race

e. Mr. Balmer never got the Nobel prize, which made everyone in the field of spectroscopy so angry, they worked extra hard

57. How could you make an ordinary atom that is minding its own business into an ion?

a. send an electron from the ground state to an excited state

b. have all the electrons in the atom drop down to the lowest available orbits

c. add more neutrons to its nucleus

d. remove one or more electrons from the atom

e. send the atom to Bayonne, New Jersey

Section 5.6: The Doppler Effect

58. Christian Doppler discovered what we now call the “Doppler Effect” by measuring:

a. the wavelengths of the Balmer lines of hydrogen

b. the intensity of the red and blue light from the same star

c. the changes in the radar gun used by his local police officers when they pointed at speeding cars

d. the changes in the colors of a rainbow when the clouds were moving fast

e. the properties of sound waves coming from a group of musicians on a moving, open railroad car

59. When a star or galaxy is moving away from us, we observe the Doppler effect by seeing the lines in its spectrum

a. red-shifted (shifted toward the red end of the light spectrum)

b. blue-shifted (shifted toward the blue or violet end of the light spectrum)

c. yellow-shifted (shifted so all the colors become a little bit yellower)

d. become darker and darker (like a blackbody)

e. you can’t fool me, the Doppler effect only applies to motions on Earth, not to the motions of the stars and galaxies

60. We observe a glowing cloud of gas in space with a spectroscope. We note that many of the familiar lines of hydrogen that we know on Earth seem to be in a different place. They are shifted toward the blue or violet end of the spectrum compared to their positions in the spectrum of glowing hydrogen gas on Earth. From this we can conclude that:

a. the cloud is much hotter than hydrogen on Earth

b. the cloud is much cooler than hydrogen on Earth

c. the cloud is moving toward us

d. the cloud is moving away from us

e. none of the above can be concluded from this observation.