# MasteringAstronomy Chapter S4

## Unlock all answers in this set

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*What do we mean by the spin of a subatomic particle?* a. The spin of a particle describes how the story of the particle is portrayed to journalists. b. It is one of the basic properties of any particle and is a measure of the particle's angular momentum. c. It describes how fast the particle is rotating on its axis at a given time; if more torque is applied, the particle spins faster. d. It is a measure of the particle's electrical charge.
b. It is one of the basic properties of any particle and is a measure of the particle's angular momentum. Remember that it is a description of a subatomic particle and not meant to imply that the particle is literally spinning like a ball.
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*Based on their spin, all particles can be classified as either __________.* a. color, flavor, or mass b. fermions or bosons c. quarks or leptons d. matter or antimatter
b. fermions or bosons The fermions then subdivide into quarks and leptons.
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*Which statement about antimatter is not true?* a. When a particle and its antiparticle meet, the result is mutual annihilation that turns all of the mass into energy. b. Every ordinary particle has a corresponding antiparticle. c. Antimatter has been hypothesized to exist but has never actually been detected. d. An antielectron (positron) is identical to an ordinary electron except it has a positive charge.
c. Antimatter has been hypothesized to exist but has never actually been detected. Antimatter is regularly produced in particle accelerators.
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*According to modern understanding, protons and neutrons are each composed of __________.* a. three quarks b. four bosons c. three leptons d. two fermions
a. three quarks A proton has two up quarks and one down quark. A neutron has one up quark and two down quarks.
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*The four fundamental forces are __________.* a. nuclear force, gravity, electric force, and magnetic force b. strong force, weak force, electric force, and magnetic force c. nuclear force, electromagnetic force, gravity, and tidal force d. strong force, weak force, electromagnetic force, and gravity
d. strong force, weak force, electromagnetic force, and gravity Note that they differ in their strength and range.
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*According to the uncertainty principle, which of the following statements is true?* a. It is impossible to measure both the mass and the momentum of a particle at the same time. b. It is impossible for science to make any meaningful predictions about nature whatsoever. c. It is impossible to measure both the speed and direction of a particle at the same time. d. It is impossible to measure both the position and the momentum of a particle at the same time.
d. It is impossible to measure both the position and the momentum of a particle at the same time. This principle can also be stated equivalently in terms of energy and time.
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*What does the exclusion principle say?* a. If a particle has a precisely defined position it is excluded from having a precisely defined momentum. b. Two fermions cannot occupy the same quantum state at the same time. c. No two particles of any type can ever occupy the same quantum state at the same time. d. The laws of quantum mechanics are excluded from our common sense.
b. Two fermions cannot occupy the same quantum state at the same time. Be sure you know what we mean by fermions and by quantum state.
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*How does degeneracy pressure differ from thermal pressure?* a. Degeneracy pressure cannot support an object against the crush of gravity, but thermal pressure can. b. Degeneracy pressure can arise in a plasma, but thermal pressure cannot. c. Degeneracy pressure continues to be felt even if an object becomes cold, but thermal pressure is drastically reduced as an object gets cold. d. Degeneracy pressure affects stars, but thermal pressure does not.
c. Degeneracy pressure continues to be felt even if an object becomes cold, but thermal pressure is drastically reduced as an object gets cold. Degeneracy pressure can therefore support an astronomical object (such as a brown dwarf or white dwarf) even as it cools.
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*What is Hawking radiation?* a. a type of high-energy radiation that comes from inside a black hole's event horizon b. a type of radiation coming from objects supported by degeneracy pressure c. a hypothesized way for black holes to gradually shrink in mass d. a type of radiation that we have detected so far only with infrared telescopes in space
c. a hypothesized way for black holes to gradually shrink in mass It gets its name because it was predicted by Stephen Hawking.
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*How is quantum tunneling important to our existence here on Earth?* a. It plays a crucial role in nuclear fusion in the Sun, so that our Sun would not shine brightly without it. b. It explains why electrons in atoms gradually fill different energy levels, thus making chemistry possible. c. It is important to understanding the law of conservation of energy. d. It explains how neutron stars are able to stay stable rather than collapsing under their strong gravity.
a. It plays a crucial role in nuclear fusion in the Sun, so that our Sun would not shine brightly without it. Calculations show that fusion would not occur in the Sun if quantum tunneling did not occur.
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*The fundamental particles of matter are* a. atoms and molecules. b. quarks and leptons. c. electrons, protons, and neutrons.
b. quarks and leptons.
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*When an electron is produced from energy in a particle accelerator, the following also always happens:* a. An antielectron (positron) is produced. b. A quark is produced. c. The electron soon disintegrates into a bunch of quarks.
a. An antielectron (positron) is produced.
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*Within an atomic nucleus, the strongest of the three forces is* a. gravity. b. electromagnetism. c. the strong force.
c. the strong force.
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*Across a distance of 1 millimeter, the strongest force acting between two protons is* a. gravity. b. electromagnetism. c. the strong force.
b. electromagnetism.
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*If we measure a subatomic particle's position very precisely, then* a. its momentum will be highly uncertain. b. its spin will be highly uncertain. c. we would be violating the uncertainty principle.
a. its momentum will be highly uncertain.
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*Aside from photons, which of the following also behave sometimes as waves and sometimes as particles?* a. fermions b. bosons c. all other subatomic particles
c. all other subatomic particles
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*Which of the following is not allowed by the exclusion principle?* a. knowing both the precise position and precise momentum of an electron b. having two electrons in the same quantum state c. having an electron with a spin that is neither up nor down
b. having two electrons in the same quantum state
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*The strength of degeneracy pressure in an object (such as a white dwarf) depends on* a. its temperature. b. its density. c. both its temperature and density.
b. its density.
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*In which one of the following objects does degeneracy pressure play the most important role?* a. a neutron star b. the Sun c. a star 10 times as massive as the Sun
a. a neutron star
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*According to the laws of quantum mechanics, empty space (a vacuum) is* a. truly empty. b. bubbling with virtual particles. c. filled with tiny black holes.
b. bubbling with virtual particles.
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*Which of the forces are unimportant on large scales because they can be felt only across distances about the size of atomic nuclei or smaller?* a. the electromagnetic force b. the strong force c. gravity d. the weak force
b. the strong force d. the weak force The strong and weak forces are both much stronger than gravity within atomic nuclei, but they have essentially no effect on larger size scales, which is why gravity can dominate them for objects such as planets, stars, and galaxies.
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*The electromagnetic force is much stronger than gravity over short distance scales. So why doesn't it dominate over gravity for large masses, such as planets, stars, and galaxies?* a. Because gravity gets stronger as the distance between two particles increases. b. Because the electromagnetic force only affects massless particles such as photons. c. Because large masses are electrically neutral. d. Because the electromagnetic force acts only over distance scales the size of molecules or smaller.
c. Because large masses are electrically neutral. The fact that there are both positive and negative electrical charges means that large objects tend to be electrically neutral, and therefore they do not interact with other large objects through the electromagnetic force. In contrast, because there is only one type of mass, gravity becomes quite strong for large masses.
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*How does the existence of helium nuclei (with 2 protons and 2 neutrons) demonstrate that there must be a force in nature that is stronger than the electromagnetic force?* a. The electromagnetic force is transmitted by photons, and they travel so fast that they would escape nuclei in a tiny fraction of a second. b. The electromagnetic force can only affect two particles at a time, so some other force must act when there are four particles. c. The electromagnetic force does not affect neutrons, so they must be held together by some other force. d. The electromagnetic force makes protons repel, so there must be a stronger force that keeps them together.
d. The electromagnetic force makes protons repel, so there must be a stronger force that keeps them together. In fact, the strong force gets its name from the fact that it is the strongest of the four forces.
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*All atoms except hydrogen atoms contain two or more protons. Protons are positively charged, so the electromagnetic force tends to make them repel each other. What force holds nuclei together, overcoming this tendency of the electromagnetic force to break nuclei apart?* a. strong force b. weak force c. gravity
a. strong force
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*We know that gravity is what holds us on the ground on Earth. But from Part A, you know that both the strong and weak forces are stronger than gravity, at least within an atomic nucleus. Why don't the strong and weak forces hold us to the ground instead of gravity?* a. because the strong and weak forces only affect electrically charged objects b. because the strong and weak forces are felt only across very short distances, such as the distance across an atomic nucleus (or smaller) c. because the larger the distance separating two objects, the stronger gravity becomes
b. because the strong and weak forces are felt only across very short distances, such as the distance across an atomic nucleus (or smaller)
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*Earth's orbit around the Sun is a consequence of __________.* a. the strong force b. the electromagnetic force c. gravity
c. gravity
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*According to the standard model, the strong force is felt when two particles exchange other particles called _____.* a. gluons b. photons c. weak bosons d. gravitons
a. gluons
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*A photon can be emitted when __________ is in motion.* a. an electrically charged particle b. any massive particle c. a weakly interacting particle
a. an electrically charged particle
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*If you place two protons a very short distance apart, they will __________.* a. glow with photons that they produce b. attract each other c. repel each other
c. repel each other
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*Which statement is true?* a. Any negatively charged particle is considered a form of antimatter. b. An antielectron is identical to an electron except that it has positive rather than negative charge. c. Antimatter is a science fiction idea that does not really exist.