Deck 4: Atomic Physics and Spectra

Question 1

A blackbody is an idealized object in physics and astronomy that

A) reflects no light and emits light in a manner determined by its temperature.
B) reflects and emits radiation in a manner that is completely determined by its temperature.
C) reflects and emits light with the same intensity at all wavelengths.
D) does not emit or reflect any radiation.

Answer 1

reflects no light and emits light in a manner determined by its temperature.

Question 2

The peak wavelength emitted in the spectrum of a blackbody is proportional to what power of the blackbody's Kelvin temperature?

A) -4
B) -1
C) 1
D) 4

Answer 2

-1

Question 3

Figure 4-2 in the text shows that a blackbody with a temperature of 3000 K emits radiation that peaks at a wavelength much longer than wavelengths in the visible part of the spectrum. This means that the object

A) is not visible but might be detected with equipment sensitive to nonvisible radiation.
B) emits no radiation, like all blackbodies.
C) emits visible radiation but not as intensely as at longer wavelengths.
D) emits no visible radiation but would emit visible radiation if its temperature were increased.

Answer 3

emits visible radiation but not as intensely as at longer wavelengths.

Question 4

A perfect blackbody is so named because it

A) reflects all radiation falling upon it but emits none of its own.
B) absorbs all radiation falling upon it and reflects none.
C) never emits radiation.
D) always emits the same amount and color of radiation regardless of its temperature.

Question 5

What changes should an observer expect to see in the resulting spectrum of emitted light from a piece of metal when it is heated slowly in an intense flame from 500 K to 1500 K?

A) The intensity of radiation would increase greatly, while the color would change from blue through white to red.
B) The intensity of radiation would increase greatly, and the color would change from red through white to blue.
C) The intensity of radiation would increase greatly, while the color would remain a dull red.
D) The intensity of radiation would increase only slightly, while the color would change from red through white to blue.

Question 6

The total amount of radiation emitted by a heated blackbody depends on its temperature and

A) how much surface area it has.
B) how much volume it has.
C) its color.
D) its chemical composition.

Question 7

Radiant energy shines on a blackbody, raising its temperature and causing it to emit radiation. The spectrum of radiation it emits depends on

A) the spectrum of the radiation it has absorbed.
B) its temperature.
C) its volume.
D) its shape.

Question 8

What overall effect on the visible spectrum of the light from a star results from the light's passage through Earth's atmosphere?

A) The intensity of the long wavelength portion of the spectrum is increased.
B) The intensity of the short wavelength portion of the spectrum is reduced.
C) The intensity is reduced uniformly across the spectrum.
D) The long and short wavelength portions of the spectrum are reduced in intensity, but the middle portion is unaffected.

Question 9

To use Wien's law to find the temperature of an object, one needs to know

A) the object's distance.
B) the object's mass.
C) the wavelength in the spectrum of the object at which the intensity is greatest.
D) the frequency of the most energetic photons emitted from the object.

Question 10

Pieces of metal are heated by varying amounts in a flame. The hottest of the pieces will be the one that shows MOST prominently which color?

A) red
B) black
C) yellow
D) blue

Question 11

To a physicist, a blackbody is defined as an object that

A) always emits the same spectrum of light, whatever its temperature.
B) reflects all radiation that falls on it, never heating up and always appearing black.
C) always appears to be black, whatever its temperature.
D) absorbs all radiation that falls on it.

Question 12

If one wants to design a device that will detect animals at night by the radiation they give off, even if the night is totally dark, to what wavelength range should the device be made sensitive?

A) ultraviolet
B) visual, like the human eye
C) No device can detect objects on a totally dark night.
D) infrared

Question 13

Two perfectly absorbing spheres have radii of R and 3R. Both are held at the same temperature. The flux of radiant energy emerging from each square meter of the larger sphere is

A) the same as the flux from the smaller sphere.
B) 3 times the flux from the smaller sphere.
C) 9 times the flux from the smaller sphere.
D) 27 times the flux from the smaller sphere.

Question 14

A clear majority of the information astronomers obtain about distant astronomical objects comes from an analysis of

A) cosmic rays.
B) meteorite fragments.
C) electromagnetic radiation.
D) radioactive decay products.

Question 15

Lin Carter, the science fiction writer, once wrote a story entitled The Green Star. Is it possible for a star to be green?

A) Yes. The surface temperature would have to be about 6000 K in order for the spectrum to peak in the green.
B) Yes, but the surface temperature would have to be at least 12,000 K in order to produce enough green to be visible.
C) No. A star cannot become hot enough to have its spectrum peak in the green.
D) No. When a star is hot enough to produce green, it also produces all wavelengths longer than green and also some shorter wavelengths, in roughly equal amounts.

Question 16

Two physicists, one on the east coast and one on the west coast of North America, discover that they have constructed ideal blackbodies in their laboratories. The two blackbodies are made from very different materials. Without conducting tests, they know that the radiation emitted by these two objects will be

A) identical if the blackbodies are at the same temperature, but not otherwise.
B) identical if the blackbodies have the same size, even if their temperatures are different.
C) different because the blackbodies were made from different materials.
D) different because the amount of light falling on the blackbodies is likely to be different in the two laboratories.

Question 17

An astronomer plots the intensity of the radiation emitted from an opaque, perfectly absorbing object at a certain temperature versus its wavelength. As the temperature increases, the wavelength at which the spectrum peaks becomes shorter and shorter. This is an example of

A) Stephan's law.
B) Kepler's first law.
C) Bode's law.
D) Wien's law.

Question 18

The amount of radiation emitted by a blackbody depends on all of these properties of the blackbody EXCEPT

A) the wavelength under consideration.
B) the temperature.
C) the chemical composition.
D) the surface area.

Question 19

An ideal blackbody in physics and astronomy is an object that

A) emits only infrared light and hence appears black to the eye.
B) does not emit or absorb any electromagnetic radiation.
C) absorbs and emits electromagnetic radiation at all wavelengths.
D) absorbs all electromagnetic radiation but emits none.

Question 20

When a rod of metal is heated intensely, its predominant color will

A) remain red as the intensity of light increases.
B) change from red through orange to white and then to blue.
C) change from blue through white, then orange, and finally red, when it becomes red-hot at its hottest.
D) be white, all colors mixed together, as the intensity of light increases.

Question 21

The temperature scale most often used by scientists is the

A) Kelvin scale.
B) Richter scale.
C) Fahrenheit scale.
D) Celsius scale.

Question 22

In what units does one measure luminosity L?

A) joule per square meter per second
B) joule per second
C) joule per square meter per second per Kelvin degree
D) joule times square meter per second

Question 23

The total radiant energy emitted from the entire surface of a blackbody is proportional to what power of the blackbody's Kelvin temperature?

A) T
B) 1/T
C) T²
D) T⁴

Question 24

In what units does one measure flux F?

A) joule per square meter per second
B) joule per second
C) joule per square meter per second per Kelvin degree
D) joule times square meter per second

Question 25

The Sun's spectrum peaks in the yellow-green region (i.e., this region is the most intense part of its spectrum). The spectrum of Rigel (the star in the knee of Rigel) peaks in the short-wavelength end of the visible spectrum. Compared with the Sun, Rigel is

A) cooler and redder.
B) cooler and whiter.
C) hotter and redder.
D) hotter and whiter.

Question 26

The symbol $\lambda$ _max represents the

A) longest wavelength in a spectrum.
B) wavelength that corresponds to the color of the light.
C) wavelength of the brightest color in the spectrum.
D) wavelength that corresponds to the color of the object that is being heated.

Question 27

An astronomer observes two stars of the same surface temperature, but one has twice the diameter of the other. How many times larger is the energy production rate per unit surface area from the larger star compared with that from the smaller star?

A) 2
B) 4
C) 16
D) They are the same.

Question 28

If curves of intensity versus wavelength are plotted for a single object at various temperatures, it is found that the curves never cross. Why is this important?

A) If the curves do not cross, then the object is not a blackbody.
B) The only situation in which the curves do not cross is when the source is a neutron star-essentially an atomic nucleus the size of a star.
C) If the curves do not cross it means that monochromatic light has been emitted from the source.
D) Because each curve is unique, in theory it is possible to determine the temperature from a single point on a blackbody curve.

Question 29

An astronomer observes two stars of the same surface temperature, but one has twice the diameter of the other. How many times larger is the luminosity from the larger star compared with that from the smaller star?

A) 2
B) 4
C) 16
D) They are the same.

Question 30

Stars A and B have the same radius, but the spectrum of star A peaks at a wavelength of 500 nm, whereas star B's spectrum peaks at 1000 nm. What is the ratio of the energy flux leaving the surface of star A to the energy flux leaving the surface of star B?

A) 1/16
B) 1/4
C) 4
D) 16

Question 31

The value of $\lambda$ _max in the spectrum given off by a heated blackbody depends on the object's

A) size.
B) color.
C) temperature.
D) chemical composition.

Question 32

Stars A and B have the same radius, but the spectrum of star A peaks at a wavelength of 500 nm, whereas star B's spectrum peaks at 1000 nm. What is the ratio of the Kelvin temperature of the surface of star A to the Kelvin temperature of the surface of star B?

A) 1/4
B) 1/2
C) 2
D) 4

Question 33

An astronomer plots the intensity of the radiation emitted from an opaque object at a certain temperature versus its wavelength. As the object's temperature increases, the total amount of energy emitted all across the spectrum increases as the fourth power of the temperature. This is an illustration of

A) the Stefan-Boltzmann law.
B) Kepler's first law.
C) Bode's law.
D) Wien's displacement law.

Question 34

An astronomer plots the blackbody curve for an object at 8000 K and then raises the temperature of the object to 12,000 K and plots the blackbody curve again. These curves

A) intersect at a point that depends on the mass of the object.
B) intersect at a point that depends on the atomic structure of the object.
C) intersect at several points. The number of crossings can be used to find the chemical composition of the object.
D) will not intersect.

Question 35

The hot, dense gas existing on the Sun emits energy

A) only at certain wavelengths and not at other wavelengths.
B) at all wavelengths, with a peak at one particular wavelength (color).
C) mostly at the longest and shortest wavelengths, with a minimum in between.
D) with the same intensity at all wavelengths. Earth's atmosphere absorbs radiation at both short and long visible wavelengths to produce the observed spectrum.

Question 36

Stars A and B have the same radius, but the spectrum of star A peaks at a wavelength of 500 nm, whereas star B's spectrum peaks at 1000 nm. What is the ratio of the luminosity of star A to the luminosity of star B?

A) 1/16
B) 1/4
C) 4
D) 16

Question 37

The ratio of the intensities of two different wavelengths in the spectrum of a blackbody depends on the blackbody's

A) size.
B) color.
C) temperature.
D) chemical composition.

Question 38

The wavelength at which the spectrum emitted from a blackbody is most intense is proportional to what power of the blackbody's Kelvin temperature?

A) T
B) 1/T
C) T²
D) T⁴

Question 39

The star Vega has a higher surface temperature than the Sun. With IR indicating infrared and UV indicating ultraviolet, Vega emits _____ IR and _____ UV flux than the Sun.

A) less; more
B) more; more
C) more; less
D) less; less

Question 40

The total radiant energy emitted per unit area from a blackbody's surface is proportional to what power of the blackbody's Kelvin temperature?

A) T
B) 1/T
C) T²
D) T⁴

Question 41

Two stars, A and B, have the same temperature, but star A is 4 times larger in diameter than star B. Which of these statements about these stars is true?

A) Stars A and B emit the same flux.
B) Stars A and B emit the same total amount of energy per second.
C) Star A emits 4 times the flux that star B emits.
D) Star A emits 16 times the flux that star B emits.

Question 42

Which of these equations represents the dependence of the total energy flux F of radiation emitted per unit area by a blackbody (e.g., star) on its temperature T with $\sigma$ a constant?

A) FT⁴ = $\sigma$
B) F⁴ = $\sigma$ T
C) F = $\sigma$ /T
D) F = $\sigma$ T⁴

Question 43

If all stars are considered to be perfect blackbodies, then which of these relationships should hold regarding the energy flux, or energy emitted per unit area, from stars?

A) All stars of the same mass emit the same energy flux.
B) All stars of the same temperature emit the same energy flux.
C) All stars of the same composition (made of exactly the same material) emit the same energy flux.
D) All stars of the same distance emit the same energy flux.

Question 44

The Stefan-Boltzmann law, which relates the energy per unit area F emitted by an object to its temperature T, F = $\sigma$ T⁴, is obeyed by what kind of object?

A) red-colored object, which absorbs blue light but reflects red light
B) only hot gases, whose atoms emit and absorb only specific colors (e.g., neon tubes)
C) blackbody, a perfect absorber and emitter of energy at all wavelengths
D) all objects, whatever their color or reflective properties

Question 45

The temperature of the surface of the Sun is 5800 K. What would be the surface temperature of a star that emits twice the energy flux (watts per square meter) that the Sun emits?

A) 6900 K
B) 4880 K
C) 11,600 K
D) 8200 K

Question 46

As a new star evolves from COOL dust and gas to a HOT star, the peak wavelength of its spectrum of emitted electromagnetic radiation could

A) change from the infrared to the visible wavelengths.
B) change from the ultraviolet to the visible range.
C) increase from the visible to infrared wavelengths.
D) remain the same.

Question 47

A piece of iron is heated from 400 K to 800 K. The total energy emitted per second by this iron will increase by a factor of

A) 296.5.
B) 4.
C) 2.
D) 16.

Question 48

When a blackbody is heated to a temperature T, its total energy flux per second per unit area F at all wavelengths (where $\sigma$ is a constant) is given by

A) F = $\sigma$ /T².
B) F = $\sigma$ T.
C) FT = $\sigma$ .
D) F = $\sigma$ T⁴.

Question 49

What is the difference between "luminosity" and "flux"?

A) Flux is determined by energy in the visible wavelengths only; luminosity is computed all across the spectrum.
B) Luminosity is the rate at which energy is emitted from an entire object; flux is luminosity per unit area.
C) Flux is the rate at which energy is emitted from an entire object; luminosity is flux per unit area.
D) They are the same thing.

Question 50

The wavelength in the middle of the yellow part of the spectrum is 575 nm. What surface temperature would the Sun have if its peak were in the middle of the yellow?

A) 4000 K
B) 5100 K
C) 6000 K
D) 8600 K

Question 51

As a newly formed star continues to contract, its temperature increases, while the chemical nature of the gas does not change. Which of these could happen to the peak wavelength of its emitted radiation?

A) The peak wavelength will move toward shorter wavelengths (e.g., IR to visible).
B) The peak wavelength will not change because it does not depend on temperature.
C) The peak wavelength will remain constant because the chemical state of the gas does not change.
D) The peak wavelength will move toward longer wavelengths (e.g., visible to IR).

Question 52

The laws governing the energy flux F and wavelength of maximum intensity $\lambda$ _max of emitted radiation from a hot, dense body whose temperature is T (where $\sigma$ and a are constants) are given by

A) F = $\sigma$ T, $\lambda$ _max = a/T⁴ .
B) F = $\sigma$ T⁴, $\lambda$ _maxT = a.
C) F = $\sigma$ T⁴, $\lambda$ _max = aT.
D) F = $\sigma$ T², $\lambda$ _maxT = a.

Question 53

Wien's law, relating the peak wavelength $\lambda$ _max of light emitted by a dense object to its temperature T, can be represented by

A) ( $\lambda$ _max = constant * T⁴.)
B) ( $\lambda$ _maxT = constant.)
C) ( $\lambda$ _max = constant/T².)
D) ( $\lambda$ _max/T = constant.)

Question 54

Which of these statements is true if the star Betelgeuse has a lower surface temperature than the Sun? (Assume that IR means infrared radiation and UV means ultraviolet radiation.)

A) Betelgeuse emits more IR and less UV flux than the Sun.
B) Betelgeuse emits more IR and more UV flux than the Sun.
C) Betelgeuse emits less IR and more UV flux than the Sun.
D) Betelgeuse emits less IR and less UV flux than the Sun.

Question 55

Cepheid variable stars pulsate regularly in size. During the contraction part of the cycle, when the star's temperature is increasing, the peak wavelength of the emitted radiation will

A) shift from the visible to the UV part of the spectrum.
B) shift from the UV to the visible part of the spectrum.
C) remain unchanged.
D) change randomly, independent of the temperature changes.

Question 56

When a solid body (or a dense gas such as a star) cools from a temperature of several thousand degrees, the "color" or wavelength of maximum emission of radiation will

A) move initially toward the red end of the spectrum, then move back toward the blue end of the spectrum as the intensity of radiation fades and eventually becomes invisible to the eye.
B) move steadily toward the blue end of the spectrum.
C) remain constant, as it depends only on the original color of the body.
D) move steadily toward the red end of the spectrum.

Question 57

Two heated spheres are at the same temperature, but one sphere has twice the radius of the other. The flux emitted from the larger sphere is

A) half the flux emitted from the smaller sphere.
B) the same as the flux emitted from the smaller sphere.
C) twice the flux emitted from the smaller sphere.
D) 4 times the flux emitted from the smaller sphere.

Question 58

By what factor does the total energy emitted per unit time at all wavelengths from an opaque, perfectly absorbing object increase if its temperature increases by a factor of 3 (e.g., approximately from room temperature to 900 K)?

A) 27
B) 3
C) 9
D) 81

Question 59

The energy flux, F, emitted by a star is the amount of

A) energy emitted by the entire star each second.
B) incoming light reflected by the star each second.
C) energy emitted by each square meter of the star's surface each second.
D) energy emitted by the star over its lifetime.

Question 60

The Sun appears yellow to the eye for a variety of reasons. Which one of these is NOT one of these reasons?

A) The sunlight that passes through Earth's atmosphere is scattered more strongly in the short wavelengths of blue and green than in the longer wavelengths of yellow.
B) The eye is most sensitive to the yellow-green part of the spectrum.
C) The white light spectrum with blue scattered out looks yellow.
D) The Sun's blackbody spectrum is sharply peaked in the yellow part of the spectrum.

Question 61

The important breakthrough in theoretical physics that was first suggested by Planck to explain the shape of the spectrum of a hot body was the

A) discovery of the formula F = $\sigma$ T⁴, which can be used to calculate the total energy flux emitted by the hot body over all wavelengths.
B) idea that light traveled at a constant speed, whatever the speed of the source.
C) idea that light is a form of electromagnetic energy transmitted at a constant speed and that there is a continuous spectrum of electromagnetic waves from gamma rays to radio waves.
D) concept that electromagnetic energy was emitted in small packets, or quanta.

Question 62

Where and by what technique was the element helium first discovered?

A) in radioactive rocks, by radioactive measurements of uranium deposits
B) on the Sun, from spectroscopy during a solar eclipse
C) in the laboratory, by examining the spectrum of heated chemicals in a flame
D) in the upper atmosphere of Earth, by studying the spectrum of the aurora, or northern lights

Question 63

A small particle of interplanetary material is heated by friction from a temperature of 400 K to 4000 K as it falls into the atmosphere of Earth and produces a meteor or a shooting star in the sky. If this object behaves like a perfect blackbody over this short time, how will its emitted radiation change as it is heated?

A) The intensity of the radiation will rise by a factor of 100, while the peak wavelength of emitted light will become shorter by a factor of 100, moving from the infrared to the ultraviolet.
B) The intensity of the radiation will rise by a factor of 10,000, while its peak wavelength will become longer by a factor of 10, moving from the visible to the infrared of heat radiation.
C) The emitted intensity of the radiation will rise by a factor of 10,000, while its peak wavelength will become shorter by a factor of 10, from infrared to red visible light.
D) The intensity of the radiation will rise by a factor of 10, while its peak wavelength will become shorter by a factor of 10, moving from the infrared to red visible light.

Question 64

What will be the peak wavelength of electromagnetic radiation emitted by a piece of iron that is just melting at a temperature of 1808 K? (Use Wien's law, which relates the peak wavelength $\lambda$ _max emitted by a body to its temperature T, and see Figure 4-2) (1 $\mu$ m = 10^-6 m).

A) 16 $\mu$ m, intermediate infrared
B) 1.89 $\mu$ m, near infrared
C) 1.6 $\mu$ m, near infrared
D) 1.04 $\mu$ m, very near infrared

Question 65

Why does the Sun look red when it is setting?

A) Red is the Sun's natural color as determined by Wien's law, but it is only when the Sun is close to the horizon that sunlight can pass through the atmosphere unfiltered.
B) When the Sun is close to the horizon, it is traveling away from the observer at great speed, and the Doppler shift makes it look red.
C) Earth's atmosphere scatters longer wavelength light more easily than shorter, so more red light is scattered out of the sunlight and into observers' eyes.
D) Earth's atmosphere scatters shorter wavelength light more easily than longer, so more red light is left to reach observers' eyes.

Question 66

What is the approximate peak wavelength of radiation emitted by (live) human beings, who are (normally) at a temperature of about 310 K?

A) 94 $\mu$ m
B) 3.1 $\mu$ m
C) 0.94 $\mu$ m
D) 9.4 $\mu$ m

Question 67

What property of helium allowed scientists to first discover its existence?

A) Helium accumulates inside meteoroids (fragments of rock and iron orbiting the Sun that, when they fall to Earth, are known as meteorites).
B) Helium refuses to combine chemically with other elements.
C) Helium absorbs light at certain wavelengths that were not characteristic of any element known at that time.
D) Helium is characteristically found in rocks containing radioactively decaying elements such as uranium.

Question 68

If a certain gas is heated and observed through a grating, a bright line spectrum will be seen. If instead a source of continuous spectrum shines through a cooler sample of this same gas, a dark absorption spectrum is observed. How do the positions of the lines in these two spectra compare?

A) All the lines in the spectrum from the hot gas will be at higher frequencies than the corresponding lines in the spectrum of the cooler gas.
B) All the lines in the spectrum from the hot gas will be at lower frequencies than the corresponding lines in the spectrum of the cooler gas.
C) The lines in the two spectra will be at the same frequencies. They will be the same spectra.
D) These two processes produce spectra by completely different means, and there will be no relationship at all between the two spectra.

Question 69

The lines Fraunhofer saw in his solar spectrum were

A) absorption lines.
B) emission lines.
C) bright lines.
D) continuum lines.

Question 70

The average temperature of Mars is less than that of Earth. What would be the relative wavelengths of the peak emissions of the spectra from these planets?

A) The emission from the two planets would peak at the same wavelength, but the radiation from Mars would be less intense than that from Earth.
B) The wavelength of peak emission from Earth would be at a longer wavelength than that from Mars.
C) The wavelength of peak emission from Mars would be at a longer wavelength than that from Earth.
D) It is not possible to predict the outcome of this experiment from the information given.

Question 71

A star whose surface temperature is 100,000 K will emit a spectrum whose peak wavelength is at

A) ultraviolet wavelengths.
B) X-ray wavelengths.
C) visible wavelengths.
D) infrared wavelengths.

Question 72

Huge fluxes of X-rays are detected from the direction of Cygnus X-1 with a spectrum that looks similar to that of a blackbody with a peak wavelength of 1.45 nm (1 nm = 10^-9 m). These X-rays are probably emitted by matter being heated as it falls into a black hole. What is the temperature of this gas?

A) 2 * 10⁶ K
B) 4205 K
C) 2 * 10^-2 K
D) 2* 10⁴ K

Question 73

Why is the sky blue?

A) The air molecules absorb red light more effectively than blue light, allowing more blue light to reach observers on Earth's surface.
B) The air molecules scatter blue light more effectively than red light, so more blue light reaches observers on Earth's surface indirectly (from directions other than the direct beam of sunlight).
C) The air molecules scatter red light more effectively than blue light, so less red light reaches observers on Earth's surface indirectly (from directions other than the direct beam of sunlight).
D) The air molecules absorb blue light more effectively than red light, making the sky appear bluer.

Question 74

If the human eye has evolved over time so that its peak wavelength sensitivity is about 0.5 $\mu$ m (1 $\mu$ m = 10^-6 m), what will be the temperature of a blackbody to which the eye will be MOST sensitive?

A) 0.58 K
B) 580 K
C) 5800 K
D) 14,240 K

Question 75

The chemical makeup of a star's surface is usually inferred by

A) theoretical methods, considering evolution of the star.
B) spectroscopy of the light emitted by the star.
C) measuring the chemical elements present in the solar wind.
D) taking a sample of the star's surface with a space probe.

Question 76

In the revolution that overtook physics around 1900, the assumption that Planck made in order to solve the problem concerning the spectrum of radiation emitted by a hot blackbody was that radiation was

A) emitted as continuous waves whose wavelength was inversely proportional to the temperature of the object.
B) emitted in small, discrete packets or quanta of energy whose individual energies were inversely proportional to the wavelength of the light.
C) emitted in small, discrete packets or quanta of energy, each quantum having an energy directly proportional to the wavelength of the light.
D) made up of small, discrete packets or quanta of energy whose individual energies were all the same, independent of wavelength.

Question 77

The element helium was first discovered and identified as a separate element

A) in natural gas originating underground, from the spectrum emitted from a flame of burning natural gas.
B) in rocks containing radioactively decaying elements such as uranium.
C) on the Sun, from the emitted spectrum from its upper atmosphere.
D) inside meteorites that had come from outer space.

Question 78

A physicist is asked to design an infrared system to detect human beings (at a normal temperature of 310 K) in darkness. What would the wavelength of peak sensitivity of the equipment need to be?

A) 9.35 $\mu$ m
B) 0.935 $\mu$ m
C) 0.00094 $\mu$ m
D) 90 $\mu$ m

Question 79

The light from a small amount of a particular chemical element, when heated in a flame, is found to consist of a

A) pattern of narrow, bright emissions at wavelengths that are specific to the element and different for each element.
B) continuous spectrum of light from which certain colors are missing or absorbed, as the absorbed colors are different for different elements.
C) pattern of narrow, bright emissions at specific wavelengths that are the same for all elements, except the relative intensities of the lines differ for different elements.
D) continuous spectrum of light whose peak wavelength is specific to the particular element.

Question 80

Which very significant fact concerning the spectra produced by hot gases, such as elements heated on the solar surface (Fraunhofer, with the solar spectrum) or in a flame (Bunsen and Kirchhoff, with laboratory spectra), was discovered in the 1800s?

A) Each chemical element produces its own characteristic pattern of spectral lines that remains fixed as the temperature increases.
B) Chemical elements emit spectral lines that move continuously toward the blue end of the spectrum as the gas temperature increases.
C) The higher the temperature, the greater the redshift of the emitted spectral lines.
D) Every chemical element produces the same set of spectral emission or absorption lines as every other chemical element, but their relative emission intensities differ.