Question 1

Which of the following best describes why we say that light is an electromagnetic wave?
A)Light can be produced only by electric or magnetic appliances.
B)Light is produced only when massive fields of electric and magnetic energy collide with one another.
C)The passage of a light wave can cause electrically charged particles to move up and down.
D)The term electromagnetic wave arose for historical reasons,but we now know that light has nothing to do with either electricity or magnetism.

Accepted Answer

The passage of a light wave causes electrically charged particles to move up and down, and this movement generates electric and magnetic fields. This is the underlying principle of electromagnetic waves, which includes light. Therefore, we say that light is an electromagnetic wave.

Question 2

Which of the following conditions lead you to see an absorption line spectrum from a cloud of gas in interstellar space?
A)The cloud is extremely hot.
B)The cloud is visible primarily because it reflects light from nearby stars.
C)The cloud is cool and very dense,so that you cannot see any objects that lie behind it.
D)The cloud is cool and lies between you and a hot star.

Accepted Answer

An absorption line spectrum is seen when a cool cloud of gas lies between the observer and a hot star. The gas in the cloud absorbs certain wavelengths of light from the star, resulting in dark absorption lines in the spectrum.

Question 3

Gamma rays have a very small
A)energy.
B)frequency.
C)mass.
D)wavelength.

Accepted Answer

Gamma rays have the shortest wavelength among all types of electromagnetic radiation, ranging between 10 picometers (pm) and 0.01 pm. Therefore, D) wavelength is the correct choice.

Question 4

Consider an atom of oxygen in which the nucleus contains 8 protons and 8 neutrons.If it is doubly ionized,what is the charge of the oxygen ion and how many electrons remain in the ion?
A)Charge = +2;number of remaining electrons = 8.
B)Charge = -2;number of remaining electrons = 10.
C)Charge = +2;number of remaining electrons = 6.
D)Charge = +2;number of remaining electrons = 2.

Accepted Answer

A doubly ionized oxygen atom has lost 2 electrons, resulting in a charge of +2. Originally having 8 electrons, it now has 6 remaining electrons.

Question 5

No object produces a perfect thermal radiation spectrum,but many objects produce close approximations.Which of the following would not produce a close approximation to a thermal radiation spectrum?
A)a hot,thin (low-density,nearly transparent)gas
B)a filament in a standard (incandescent)light bulb
C)a star
D)you

Accepted Answer

A hot, thin gas would not produce a close approximation to a thermal radiation spectrum because it lacks the necessary density and opacity to produce a continuous spectrum. Instead, it would produce an emission line spectrum with only a few specific wavelengths of light being emitted.

Question 6

Suppose that two stars are identical in every way-for example,same distance,same mass,same temperature,same chemical composition,and same speed relative to Earth-except that one star rotates faster than the other.Spectroscopically,how could you tell the stars apart?
A)The faster rotating star has wider spectral lines than the slower rotating star.
B)The faster rotating star will have an emission line spectrum while the slower rotating star will have an absorption line spectrum.
C)The peak of thermal emission will be at a shorter wavelength for the faster rotating star than for the slower rotating star.
D)There is no way to tell the stars apart spectroscopically,because their spectra will be identical.

Accepted Answer

The faster rotating star will have broader spectral lines due to the Doppler shift of the rotation. The rotation causes the gas on the star's equator to move towards the observer, causing a blueshift in the spectral lines, and away from the observer causing a redshift in the spectral lines. This broadening of spectral lines is called rotational broadening. Therefore, the faster rotating star will have wider spectral lines than the slower rotating star.

Question 7

Suppose that Star X and Star Y both have redshifts,but Star X has a larger redshift than Star Y.What can you conclude?
A)Star X is moving away from us faster than Star Y.
B)Star Y is moving away from us faster than Star X.
C)Star X is hotter than Star Y.
D)Star X is moving away from us and Star Y is moving toward us.

Accepted Answer

Redshift is caused by the Doppler effect, which occurs when an object is moving away from us. The greater the redshift, the faster the object is moving away from us. Therefore, Star X, with a larger redshift, is moving away from us faster than Star Y.

Question 8

Betelgeuse is the bright red star representing the left shoulder of the constellation Orion.All the following statements about Betelgeuse are true.Which one can you infer from its red color?
A)It is much brighter than the Sun.
B)Its surface is cooler than the surface of the Sun.
C)It is much more massive than the Sun.
D)It is moving away from us.

Accepted Answer

The color of a star is a good indicator of its surface temperature. Red stars are cooler than yellow and blue stars, so we can infer that Betelgeuse's surface is cooler than the surface of the Sun.

Question 9

Suppose a photon has a frequency of 300 million hertz (300 megahertz).What is its wavelength?
A)1 meter
B)1/300,000 meter
C)300 million meters
D)A photon's wavelength cannot be determined from its frequency.

Accepted Answer

The wavelength ($\lambda$) of a photon can be calculated using the formula $\lambda = \frac{c}{f}$, where $c$ is the speed of light ($3 \times 10^8$ meters per second) and $f$ is the frequency. For a frequency of 300 million hertz (300 MHz), the wavelength is $\frac{3 \times 10^8 \, \text{m/s}}{300 \times 10^6 \, \text{Hz}} = 1$ meter.

Question 10

Suppose you are listening to a radio station that broadcasts at a frequency of 97 Mhz (megahertz).Which of the following statements is true?
A)The radio waves from the radio station are causing electrons in your radio's antenna to move up and down 97 million times each second.
B)The radio waves from the radio station have a wavelength of 97 million meters.
C)The "radio waves" received by your radio are not light waves like those we talk about in astronomy,but rather are a special type of sound wave.
D)The radio station broadcasts its signal with a power of 97 million watts.

Accepted Answer

The frequency of 97 MHz means that the radio waves from the station are oscillating or moving up and down 97 million times per second. This oscillation causes electrons in the antenna of the radio to move up and down as well, creating an electrical signal that can be converted into sound. Option B is incorrect because the wavelength of a frequency of 97 MHz is around 3 meters, not 97 million meters. Option C is also incorrect because "radio waves" are electromagnetic waves, not sound waves. Option D is also incorrect because the frequency of 97 MHz provides information about the number of oscillations per second, not the power of the signal.

Question 11

All of the following statements about the Sun's corona are true.Which one explains why it is a source of X-rays?
A)The temperature of the corona's gas is some 1 to 2 million Kelvin.
B)The corona lies above the visible surface of the Sun.
C)The corona's gas consists mostly of hydrogen and helium.
D)The corona's structure is largely shaped by magnetic fields.

Accepted Answer

The high temperature of the corona's gas, some 1 to 2 million Kelvin, is what makes it a source of X-rays.

Question 12

If we observe one edge of a star to be redshifted and the opposite edge to be blueshifted,what can we conclude about the star?
A)We must actually be observing planets orbiting the star in opposite directions,not the star planet itself.
B)The star is rotating.
C)The star is in the process of falling apart.
D)The star is in the process of formation.

Accepted Answer

If one edge of a star is redshifted and the opposite edge is blueshifted, it indicates that the star is rotating. This is because the light emitted from the edge rotating towards us will be blueshifted, while the light emitted from the edge rotating away from us will be redshifted. Therefore, we can conclude that the star is not falling apart or in the process of formation, and it is unlikely to be planets orbiting in opposite directions.

Question 13

Which of the following statements about thermal radiation is always true?
A)A hot object emits more radiation per unit surface area than a cool object.
B)A cold object produces more total infrared and radio emission per unit surface area than a hot object.
C)A hot object produces more total infrared emission than a cooler object.
D)All the light emitted by hot object has higher energy than the light emitted by a cooler object.

Accepted Answer

According to the Stefan-Boltzmann law, a hot object emits more radiation per unit surface area than a cool object.

Question 14

Studying a spectrum from a star can tell us a lot.All of the following statements are true except one.Which statement is not true?
A)The total amount of light in the spectrum tells us the star's radius.
B)The peak of the star's thermal emission tells us its temperature: hotter stars peak at shorter (bluer)wavelengths.
C)We can identify chemical elements present in the star by recognizing patterns of spectral lines that correspond to particular chemicals.
D)Shifts in the wavelengths of spectral lines compared to the wavelengths of those same lines measured in a laboratory on Earth can tell us the star's speed toward or away from us.

Accepted Answer

The total amount of light in the spectrum does not directly tell us the star's radius. The radius of a star can be estimated based on its distance from Earth and its apparent brightness.

Question 15

Laboratory measurements show hydrogen produces a spectral line at a wavelength of 486.1 nanometers (nm).A particular star's spectrum shows the same hydrogen line at a wavelength of 486.0 nm.What can we conclude?
A)The star is moving away from us.
B)The star is getting hotter.
C)The star is moving toward us.
D)The star is getting colder.

Accepted Answer

This is an example of the Doppler effect which shows that the apparent wavelength of light emitted by a source changes if the source is moving relative to the observer. In this case, the star's spectral line of hydrogen is shifted to a shorter wavelength, indicating that the star is moving towards us.

Question 16

Suppose you had molecular oxygen (O₂)chilled enough so that it was in liquid form.Which of the following best describes the phase changes that would occur as you heated the liquid oxygen to high temperature?
A)It would evaporate into a gas,then the molecules would dissociate into individual oxygen atoms,then the atoms would become increasingly ionized as you continued to raise the temperature.
B)The liquid molecules would quickly dissociate into a liquid of individual oxygen atoms.These atoms would then evaporate into a gas,and then become ionized to make a plasma.
C)It would vaporize into a gas,then the molecules would lose electrons until no electrons were left,then the molecules would dissociate into individual oxygen nuclei.
D)The cold temperature would first cause the oxygen to solidify.The solid would then sublimate into a gas,which would then become a plasma as the molecules lost their electrons,until finally it consisted of bonded pairs of oxygen nuclei stripped bare of any electrons.

Accepted Answer

As the liquid oxygen is heated, it would first evaporate into a gas. With continued heating, the molecules would dissociate into individual oxygen atoms, and then as the temperature increases even further, the atoms would become increasingly ionized, forming a plasma. This process is known as plasma dissociation or plasma ionization. Choice B is incorrect because the liquid oxygen would not quickly dissociate into individual oxygen atoms, it would first need to become a gas. Choice C is incorrect because the process described is not possible - molecules cannot lose electrons until they no longer have any left. Choice D is incorrect because the cold temperature would not cause the oxygen to solidify, but rather it would liquefy.

Question 17

The planet Neptune is blue in color.How would you expect the spectrum of visible light from Neptune to be different from the visible-light spectrum of the Sun?
A)The two spectra would have similar shapes,except Neptune's spectrum would be missing a big chunk of the red light that is present in the Sun's spectrum.
B)The two spectra would have similar shapes,except Neptune's spectrum would be missing a big chunk of the blue light that is present in the Sun's spectrum.
C)Neptune's spectrum would peak at a much longer wavelength than the Sun's spectrum.
D)There is no way to predict the answer to this question,since planets and stars are made of such different things.

Accepted Answer

Neptune appears blue because its atmosphere absorbs red light and reflects blue light. Therefore, its spectrum would be missing a significant portion of the red light present in the Sun's spectrum, which emits a broad range of visible light.

Question 18

Which of the following statements about electrons is not true?
A)Electrons orbit the nucleus rather like planets orbiting the Sun.
B)Within an atom,an electron can have only particular energies.
C)An electron has a negative electrical charge.
D)Electrons have very little mass compared to protons or neutrons.
E)Electrons can jump between energy levels in an atom only if they receive or give up an amount of energy equal to the difference in energy between the energy levels.

Accepted Answer

Electrons do not orbit the nucleus like planets orbiting the Sun. The correct description is that electrons exist in a cloud or shell around the nucleus and their movement is described by a probability distribution.

Question 19

Each of the following describes an "Atom 1" and an "Atom 2." In which case are the two atoms different isotopes of the same element?
A)Atom 1: nucleus with 6 protons and 8 neutrons,surrounded by 6 electrons; Atom 2: nucleus with 7 protons and 8 neutrons,surrounded by 7 electrons.
B)Atom 1: nucleus with 7 protons and 8 neutrons,surrounded by 7 electrons; Atom 2: nucleus with 7 protons and 7 neutrons,surrounded by 7 electrons.
C)Atom 1: nucleus with 8 protons and 8 neutrons,surrounded by 8 electrons; Atom 2: nucleus with 8 protons and 8 neutrons,surrounded by 7 electrons.
D)Atom 1: nucleus with 4 protons and 5 neutrons,surrounded by 4 electrons; Atom 2: nucleus with 5 protons and 5 neutrons,surrounded by 4 electrons.

Accepted Answer

Atom 1 has 7 protons and 8 neutrons, while Atom 2 has 7 protons and 7 neutrons. These are different isotopes of the same element, which is nitrogen (N).

Question 20

Which of the following statements about X-rays and radio waves is not true?
A)X-rays travel through space faster than radio waves.
B)X-rays have shorter wavelengths than radio waves.
C)X-rays and radio waves are both forms of light,or electromagnetic radiation.
D)X-rays have higher frequency than radio waves.

Accepted Answer

X-rays and radio waves both travel at the speed of light, so they have the same speed. Therefore, statement A is not true.

Quiz 5: Light and Matter: Reading Messages from the Cosmos

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

Which of the following conditions lead you to see an absorption line spectrum from a cloud of gas in interstellar space?

Gamma rays have a very small

Consider an atom of oxygen in which the nucleus contains 8 protons and 8 neutrons.If it is doubly ionized,what is the charge of the oxygen ion and how many electrons remain in the ion?

No object produces a perfect thermal radiation spectrum,but many objects produce close approximations.Which of the following would not produce a close approximation to a thermal radiation spectrum?

Suppose that two stars are identical in every way-for example,same distance,same mass,same temperature,same chemical composition,and same speed relative to Earth-except that one star rotates faster than the other.Spectroscopically,how could you tell the stars apart?

Suppose that Star X and Star Y both have redshifts,but Star X has a larger redshift than Star Y.What can you conclude?

Betelgeuse is the bright red star representing the left shoulder of the constellation Orion.All the following statements about Betelgeuse are true.Which one can you infer from its red color?

Suppose a photon has a frequency of 300 million hertz (300 megahertz) .What is its wavelength?

Suppose you are listening to a radio station that broadcasts at a frequency of 97 Mhz (megahertz) .Which of the following statements is true?

All of the following statements about the Sun's corona are true.Which one explains why it is a source of X-rays?

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

Which of the following statements about thermal radiation is always true?

Studying a spectrum from a star can tell us a lot.All of the following statements are true except one.Which statement is not true?

Laboratory measurements show hydrogen produces a spectral line at a wavelength of 486.1 nanometers (nm) .A particular star's spectrum shows the same hydrogen line at a wavelength of 486.0 nm.What can we conclude?

Suppose you had molecular oxygen (O₂) chilled enough so that it was in liquid form.Which of the following best describes the phase changes that would occur as you heated the liquid oxygen to high temperature?

The planet Neptune is blue in color.How would you expect the spectrum of visible light from Neptune to be different from the visible-light spectrum of the Sun?

Which of the following statements about electrons is not true?

Each of the following describes an "Atom 1" and an "Atom 2." In which case are the two atoms different isotopes of the same element?

Which of the following statements about X-rays and radio waves is not true?