c5concept

Part A

Suppose you have a 100-watt light bulb that you leave turned on for one minute. How much energy does it use?

Hint A.1
Study Section 5.1, and don't forget that there are 60 seconds in 1 minute.

ANSWER:

6,000 joules 100 joules. 100 watts 6,000 watts

Part B

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

Hint B.1
Mhz stands for megahertz, which is a million hertz. Review the definition of hertz in your text.

ANSWER:

The "radio waves" that are received by your radio are not light waves like those we talk about in astronomy, but rather are a special type of sound wave. 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. The radio waves from the radio station have a wavelength of 97 million meters. The radio station broadcasts its signal with a power of 97 million watts.

Part D

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

Hint D.1
The speed of light is 300 million m/s.

ANSWER:

A photon's wavelength cannot be determined from its frequency. 1 meter. 300 million meters. 1/300,000 meter.

Part E

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

Hint E.1
Study Section 5.2.

ANSWER:

Light is produced only when massive fields of electric and magnetic energy collide with one another. Light can be produced only by electric or magnetic appliances. The term electromagnetic wave arose for historical reasons, but we now know that light has nothing to do with either electricity or magnetism. The passage of a light wave can cause electrically charged particles to move up and down.

Part F

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

Hint F.1
Study Section 5.2.

ANSWER:

X rays and radio waves are both forms of light, or electromagnetic radiation. X rays have shorter wavelengths than radio waves. X rays travel through space faster than radio waves. X rays have higher frequency than radio waves.

Part G

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?

Hint G.1
Study Section 5.3.

ANSWER:

Atom 1: nucleus with 8 protons and 8 neutrons, surrounded by 8 electronsAtom 2: nucleus with 8 protons and 8 neutrons, surrounded by 7 electrons Atom 1: nucleus with 6 protons and 8 neutrons, surrounded by 6 electronsAtom 2: nucleus with 7 protons and 8 neutrons, surrounded by 7 electrons Atom 1: nucleus with 7 protons and 8 neutrons, surrounded by 7 electronsAtom 2: nucleus with 7 protons and 7 neutrons, surrounded by 7 electrons Atom 1: nucleus with 4 protons and 5 neutrons, surrounded by 4 electronsAtom 2: nucleus with 5 protons and 5 neutrons, surrounded by 4 electrons

Part H

Suppose you had some 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 up?

Hint H.1
Study Section 5.3

ANSWER:

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. 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. It would sublime into a gas, then the molecules would lose electrons until no electrons were left, then the molecules would dissociate into individual oxygen nuclei. The cold temperature would first cause the oxygen to solidify. The solid would then sublime 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.

Part I

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?

Hint I.1
Study Section 5.3.

ANSWER:

Charge is +2; number of remaining electrons = 8. Charge is --2; number of remaining electrons = 10. Charge is +2; number of remaining electrons = 6. Charge is +2; number of remaining electrons = 2.

Part J

Which of the following statements about electrons is NOT true?

Hint J.1
Study Section 5.3

ANSWER:

Electrons orbit the nucleus rather like planets orbiting the Sun. 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. Within an atom, an electron can have only particular energies. Electrons have very little mass compared to protons or neutrons. An electron has a negative electrical charge.

Part K

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

Hint K.1
Study Section 5.4

ANSWER:

The cloud is cool and very dense, so that you cannot see any objects that lie behind it. The cloud is extremely hot. The cloud is cool and lies between you and a hot star. The cloud is visible primarily because it reflects light from nearby stars.

Part L

The following 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?

Hint L.1
Study Section 5.3 and 5.4.

ANSWER:

B A C D

Part M

If an electron at level 1 in a hydrogen atom absorbs 10.2 eV of energy, it moves to level 2. What typically happens next?

Hint M.1
Study Section 5.3.

ANSWER:

A different electron drops into level 1, since it is now unoccupied. The electron returns to level 1 by emitting an ultraviolet photon with 10.2 eV of energy. The electron jumps to level 3 as soon as it absorbs any additional energy. The electron remains in level 2 until it absorbs an additional 10.2 eV of energy.

Part N

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?

Hint N.1
Study Section 5.4.

ANSWER:

a star you a filament in a light bulb hot thin (diffuse, nearly transparent) gas

Part O

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

Hint O.1
Study Section 5.4.

ANSWER:

All the light emitted by hot object has higher energy than the light emitted by a cooler object. A hot object produces more total infrared emission than a cooler object. A cold object produces more total infrared and radio emission per unit surface area than a hot object. A hot object emits more radiation per unit surface area than a cool object.

Part P

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?

Hint P.1
Study Sections 5.4 and 5.5.

ANSWER:

It is much more massive than the Sun. It is much brighter than the Sun. Its surface is cooler than the surface of the Sun. It is moving away from us.

Part Q

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?

Hint Q.1
Study Sections 5.4 and 5.5.

ANSWER:

Neptune's spectrum would peak at a much longer wavelength than the Sun's spectrum. 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. There is simply no way to predict the answer to this question, since planets and stars are made of such different things. 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.

Part R

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

Hint R.1
Study Sections 5.4 and 5.5.

ANSWER:

The corona lies above the visible surface of the Sun. The corona's structure is largely shaped by magnetic fields. The temperature of the corona's gas is some 1 to 2 million Kelvin. The corona's gas consists mostly of hydrogen and helium.

Part S

From laboratory measurements, we know that a particular spectral line formed by hydrogen appears at a wavelength of 486.1 nanometers (nm). The spectrum of a particular star shows the same hydrogen line appearing at a wavelength of 486.0 nm. What can we conclude?

Hint S.1
Study Sections 5.4 and 5.5.

ANSWER:

The star is getting colder. The star is moving away from us. The star is getting hotter. The star is moving toward us.

Part T

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

Hint T.1
Study Section 5.5.

ANSWER:

Star X is moving away from us faster than Star Y. Star X is hotter than Star Y. Star X is coming toward us faster than Star Y. Star Y is moving away from us faster than Star X. Star X is moving away from us and Star Y is moving toward us.

Part U

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?

Hint U.1
Study Section 5.5.

ANSWER:

The planet is rotating. We must actually be observing moons orbiting the planet in opposite directions, not the planet itself. The planet is in the process of falling apart. The planet is in the process of formation.

Part V

Studying a spectrum from a star can tell us a lot. All of the following statements are true except one. Which one?

Hint V.1
Consider all that you have learned about light in Chapter 5.

ANSWER:

We can identify chemical elements present in the star by recognizing patterns of spectral lines that correspond to particular chemicals. The total amount of light in the spectrum tells us the star's radius. 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. The peak of the star's thermal emission tells us its temperature: hotter stars peak at shorter (bluer) wavelengths.