Chapter 05 Mastering Astronomy

The diagram represents energy levels in a hydrogen atom. The labeled transitions (A through E) represent an electron moving between energy levels. Which labeled transition represents an electron that absorbs a photon with 10.2 eV of energy?

B

Which of the following statements is true of green grass?

It absorbs red light and reflects green light.

Which of the following best describes why the Sun's spectrum contains black lines over an underlying rainbow?

The Sun's hot interior produces a continuous rainbow of color, but cooler gas at the surface absorbs light at particular wavelengths.

The diagram represents energy levels in a hydrogen atom. The labeled transitions (A through E) represent an electron moving between energy levels. Suppose that an electron in a hydrogen atom absorbs 10.2 eV of energy, so that it moves from level 1 to level 2. What typically happens next?

The electron returns to level 1 by emitting an ultraviolet photon with 10.2 eV of energy.

Which of the following best describes why we say that light is an electromagnetic wave?

The passage of a light wave can cause electrically charged particles to move up and down.

One star is emitting primarily visible light and another star is emitting primarily infrared light. Which star is hotter?

The star emitting visible light.

For an object producing a thermal spectrum, a higher temperature causes the spectrum to have ___________.

a peak intensity located at shorter wavelength

Blue light hitting a red sweatshirt is an example of

absorption

What type of visible light spectrum does the Sun produce?

an absorption line spectrum

Spectra from neutral atoms compared with spectra from ionized atoms of the same element

have different sets of spectral lines.

An atom that has fewer electrons than protons is called a(n) ________.

ion

Thermal radiation gets its name because

its spectrum depends on the temperature of the object emitting it

When an electron drops to a lower energy level in an atom

light at a wavelength specific to the change in energy levels is emitted.

Red light has a _____ wavelength and a _____ frequency than does blue light.

longer, lower

Red light has a lower energy per photon than blue light. Therefore, red light has

lower frequency, longer wavelength than blue light.

In the illustration of the solar spectrum, the upper left portion of the spectrum shows the __________ visible light.

lowest frequency

If you have a telescope that is observing light with wavelengths of a few meters, you are observing __________.

radio waves

From lowest energy to highest energy, which of the following correctly orders the different categories of electromagnetic radiation?

radio, infrared, visible light, ultraviolet, X-rays, gamma rays

White light hitting white paper is an example of

reflection or scattering.

The simplified spectra for four stars is shown here. Which star has the lowest temperature?

star D (purple line)

Notice that the Sun's spectrum appears brightest (or most intense) in the yellow-green region. This fact tells us __________.

the approximate temperature of the Sun's surface

The absorption line spectrum shows what we see when we look at a hot light source (such as a star or light bulb) directly behind a cooler cloud of gas. Suppose instead that we are looking at the gas cloud but the light source is off to the side instead of directly behind it. In that case, the spectrum would __________.

be an emission line spectrum

Suppose that Mars had a higher surface temperature. How would its spectrum be different?

The peak in the infrared would be at shorter wavelength.

Which of the following describes the light that can be detected from a person?

The person reflects many wavelengths of visible light and emits a continuum of wavelengths of infrared light.

If we observe one edge of a planet to be redshifted and the opposite edge to be blueshifted, what can we conclude about the planet?

The planet is rotating.

The spectra of most galaxies show redshifts. This means that their spectral lines ________.

have wavelengths that are longer than normal

Click "show" for the emission line spectrum, then click "choose gases" and study the emission line spectrum for neon. The neon "OPEN" sign appears reddish-orange because __________.

neon atoms emit many more yellow and red photons than blue and violet photons

Suppose that you had "X-ray vision" that allowed you to see X rays. What would you notice when you looked at a friend standing near you that you could not notice with your visible light vision alone?

nothing.

Which of the following are forms of light (electromagnetic radiation)?

Gamma rays, x rays, visible light, infrared, microwaves, radio waves, ultraviolet

X ray photons have a _____ wavelength, _____ frequency, and _____ energy than do ultraviolet photons.

shorter, higher, higher

Suppose we want to know what the Sun is made of. What should we do?

Compare the wavelengths of lines in the Sun's spectrum to the wavelengths of lines produced by chemical elements in the laboratory.

Consider a planet orbiting another star that is very similar to our Sun. Assume the planet is about the size of Earth and has an Earth-like orbit around its star. Which of the following statements are true about the light coming from the star and planet?

- The planet emits virtually all its light as infrared light. - The star's spectrum peaks in visible light. - The star emits much more total light than the planet.

An atom of the element gold has an atomic number of 79 and an atomic mass number of 197. If it is neutral, how many protons, neutrons, and electrons does it have?

79 protons, 118 neutrons, 79 electrons

Which statement about photons of light is true?

An infrared photon has less energy than an X-ray photon, but travels at the same speed.

Most continuous spectra are examples of what we also call thermal radiation spectra. Why do we call them "thermal" spectra?

Because the peak wavelength of the spectrum depends on the temperature of the object producing the spectrum.

Most interstellar clouds are made mostly of hydrogen (because hydrogen is the most common element in the universe). Why are these clouds usually dominated by the color red?

Because the strongest visible emission lines from hydrogen are red.

Incandescent light bulbs emit thermal radiation because their filaments are heated to about 2500 Kelvin. LED light bulbs emit only at particular visible wavelengths. Why do incandescent bulbs require more energy to shine with the same amount of visible light as LED bulbs?

Incandescent bulbs emit most of their energy as infrared light.

Why does Mars appear reddish in color?

It reflects most of the Sun's red light while absorbing most of its blue light.

Imagine being on the Moon and looking at the thermal radiation spectrum of Earth. How would it compare to the spectra shown on the graph in the video?

It would be very similar to the spectrum of the human.

Which of the following procedures would allow you to make a spectrum of the Sun similar to the one shown, though with less detail?

Pass a narrow beam of sunlight through a prism.

Suppose you see two stars: a blue star and a red star. Which of the following can you conclude about the two stars? Assume that no Doppler shifts are involved. (Hint: Think about the laws of thermal radiation.)

The blue star has a hotter surface temperature than the red star.

When the atom's electrons step down to lower energy levels in a thin cloud of hot gas, what is produced?

an emission line spectrum

Compared to a cold object, a hotter object of the same size emits most of its light at __________ wavelengths and emits _____ light overall.

shorter, more

Any spectrum can be displayed either in photographic form as shown to the left or as a graph. Which of the following graphs could represent a portion of the Sun's visible light spectrum?

the absorption spectrum

Suppose you want to know the chemical composition of a distant star. Which piece of information is most useful to you?

the wavelengths of spectral lines in the star's spectrum

Consider an atom of zinc in which the nucleus contains 30 protons and 35 neutrons. What is its atomic number and atomic mass number?

The atomic number is 30, and the atomic mass number is 65.

Study the graph of the intensity of light versus wavelength for continuous spectra, observing how it changes with the temperature of the light bulb. Recall that one of the laws of thermal radiation states that a higher-temperature object emits photons with higher average energy (Wien's law). This law is illustrated by the fact that for a higher temperature object, the graph peaks at __________.

a shorter wavelength.

Doppler shifted hydrogen absorption lines are seen in the spectrum of a star. The hydrogen line at 656.28 nm is seen to be shifted to 656.50 nm. How fast is the star moving (Note: The speed of light is approximately 300,000 km/s, or 3 × 105 km/s)?

about 100 km/s away from us