ASTR 1401 Chapter 9

Quantum mechanics is a branch of physics that applies on very small scales. a branch of physics that deals with the properties of gases. the idea that quantitative methods are needed to understand physics. a branch of physics that deals with the curvature of spacetime. the idea that mechanics can be understood only if we first understand quantums.

Which of the following statements best describes the quantum property spin? Spin is a property that applies only to large objects, like baseballs. Spin is not a fundamental property but rather something that can change randomly at any time. Spin is not meant to be taken literally but measures the inherent angular momentum of a subatomic particle. Spin is a measure of the rotation rate of a subatomic particle. Spin is a measure of the rate at which a particle spins around (orbits) another particle.

The characteristic that distinguishes fermions from bosons is their size. their spin. their mass. their speed of travel. their electric charge.

An up quark (u) has a charge +2/3, and a down quark (d) has a charge of - 1/3. Which of the following describes a proton? udd uud uuu ddd

Protons and neutrons are leptons. are composed of the same number of quarks. are fundamental particles. have exactly the same mass. have exactly the same charge.

Which of the following statements about electrons is not true? Electrons are both particles and waves. Electrons are one of the six known types of lepton. Electrons have about the same mass as protons. In an atom, an electron can have two possible values for its spin, usually called spin up and spin down. They carry a negative charge.

Which of the following statements about neutrinos is not true? Neutrinos have a mass that is much smaller than the mass of an electron. Neutrinos do not respond to the force of gravity. There are three types of neutrinos, and these represent three of the six known types of lepton. Neutrinos are neither attracted nor repelled by electrically charged particles. Neutrinos do not respond to the strong nuclear force.

The two families of fundamental particles out of which all ordinary matter is made are leptons and photons. leptons and quarks. electrons and neutrinos. quarks and neutrinos. protons and neutrons.

What happens when a particle and its corresponding particle of antimatter meet? No one knows, since antimatter is only theoretical and not known to really exist. The particles join together to make an antimatter atom. The particle and the antiparticle are annihilated, turning all their mass into energy. The particles collide and then bounce back apart. They live happily ever after.

The four fundamental forces are strong force, weak force, electromagnetic force, gravity. strong force, weak force, electric force, magnetic force. nuclear force, electromagnetic force, gravity, tidal force. nuclear force, gravity, tidal force, magnetic force.

Which of the following is not a fundamental force? weak force electromagnetic force strong force degeneracy pressure gravity

Which force is strongest within an atomic nucleus? strong weak electromagnetic gravity They are all equal.

Which force is strongest beyond an atomic nucleus? strong weak electromagnetic gravity They are all equal.

Which of the following is not an exchange particle (that mediates the four fundamental forces of nature)? weak bosons leptons gravitons photons gluons

Suppose that, through the malicious act of an eight-dimensional alien being, the strong force was suddenly turned off throughout the universe. What would happen almost immediately to atoms? nothing Electrons would fall into the nuclei of atoms. Atoms would be immediately ionized. The nuclei of atoms would fall apart. Gravity would become the strongest force in nature.

The two fundamental laws that lie at the heart of quantum mechanics are the law of quantum degeneracy and the law of inviolate absolutes. the uncertainty principle and the exclusion principle. the law of conservation of angular momentum and the law of conservation of energy. the absoluteness of the speed of light and the equivalence principle. the law of conservation of energy and the electromagnetic force law.

According to the uncertainty principle, which of the following statements is true? It is impossible to measure both the mass and the velocity of a particle at the same time. God does not play dice. It is impossible to measure both the position and the velocity of a particle at the same time. It is impossible to measure both the speed and the direction of a particle at the same time. It is impossible for science to make any meaningful predictions about nature whatsoever.

Which of the following best describes the meaning of the uncertainty principle as applied to an electron bound in an atom? The electron follows a precise path around the nucleus, but it is impossible for us to actually measure this path. The electron is actually a precisely defined sphere surrounding the nucleus rather than a point, which explains why we cannot locate it at a single position. The electron does not really exist, and what we perceive as an electron is really just an ill-defined energy field. The electron is both a particle and a wave and is therefore "smeared out" around the nucleus. The electron always has a clearly defined position and velocity, but the laws of nature are set up so that, if we measure one, the other becomes instantly hidden from view.

What law of nature explains why electrons must arrange themselves in atoms with no more than two per energy level, thus making chemistry possible? the exclusion principle the electromagnetic force law the law of conservation of energy the law of conservation of angular momentum the uncertainty principle

Which of the following statements best describes the exclusion principle? If a particle has a precisely defined position, it is excluded from having a precisely defined momentum. The laws of quantum mechanics are excluded from applying to large objects made of many atoms. The laws of quantum mechanics are excluded from our common sense. Two fermions cannot occupy the same quantum state at the same time. Two photons cannot be in the same place at the same time.

Why is there a limit to how much compression can be counterbalanced by electron degeneracy pressure? At extreme compression, the electron speeds approach the speed of light and therefore cannot increase further. The exclusion principle excludes electrons from exerting more pressure than the uncertainty principle would otherwise allow. At extreme compression, electrons are forced to stop moving, and once stopped there is nothing more they can do. Electrons are very small and are simply incapable of exerting much pressure. At extreme compression, atoms are fully ionized, so electrons go free and can no longer exert pressure.

Which of the following statements about degeneracy pressure is not true? Explaining the origin of degeneracy pressure requires both the quantum mechanical exclusion principle and the uncertainty principle. Degeneracy pressure halts the collapse of neutron stars. Degeneracy pressure stops the gravitational collapse of white dwarfs. Degeneracy pressure arises only with fermions (such as electrons, protons, and neutrons) and not with bosons (such as photons or helium nuclei). Degeneracy pressure stops the gravitational collapse of ordinary (main-sequence) stars like the Sun.

Which of the following statements about quantum tunneling is true? It is used in modern electronics, and, in fact, our modern-day computers would not work without it. It plays a crucial role in nuclear fusion in the Sun. It allows electrons and other subatomic particles to pass through wall-like energy barriers even when it seems they do not have enough energy to get through the barriers. Although it has been observed to occur, it violates all other known laws of nature, and explaining it therefore represents a major challenge to physicists. A, B, and C are true, but D is not

Which of the following best explains the phenomenon of black hole evaporation? Black hole evaporation is a virtual process, meaning that it has been theorized by astrophysicists but doesn't really occur. Particles (or antiparticles) are created by a quantum mechanical effect near, but outside, the event horizon of the black hole. The law of conservation of energy maintains that the black hole must lose energy to "pay" for the creation of this mass. Virtual particles created near the black hole are constantly annihilating each other, causing a very high temperature even if the black hole has no accretion disk. This high temperature provides escape velocity for the virtual particles, causing the entire "cloud" of virtual particles to expand away into space. Particles (or antiparticles) are occasionally ejected from within the event horizon, causing the black hole to lose mass. Due to high temperatures in the accretion disk around a black hole, material evaporates from the black hole like water evaporating from the ocean.

Which of the following statements about Hawking radiation is not true, at least according to our current understanding? It was first predicted by Stephen Hawking in the 1970s. It has never yet been observed. It causes black holes to slowly shrink in mass. It occurs when real particles are created from the gravitational potential energy of a black hole. It represents a strange form of radiation that emerges from within the event horizon of a black hole.