Astronomy Chapter 4 Test Questions – Flashcards
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index of refraction (n)
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The ratio of the speed of light in a vacuum (c) to the speed of light in an optical medium (v).
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light-year (ly)
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The distance that light travels in 1 year-about 9 trillion kilometers (km).
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parsec (pc)
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The distance to a star with a parallax of 1 arcsecond using a base of 1 astronomical unit (AU). One parsec is approximately 3.26 light- years.
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wave
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A disturbance moving along a surface or passing through a space or a medium.
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electric force
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The force exerted on a charged particle by an electric field.
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electromagnetic wave
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A wave consisting of oscillations in the electric-field strength and the magnetic-field strength.
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magnetic force
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A force associated with, or caused by, the relative motion of charges.
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amplitude
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In a wave, the maximum deviation from its undisturbed or relaxed position. For example, in a water wave the amplitude is the vertical distance from crests to the undisturbed water level.
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frequency
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The number of times per second that a periodic process occurs. Unit: hertz (Hz), 1/s.
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hertz (Hz)
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A unit of frequency equivalent to cycles per second
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electromagnetic radiation
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A traveling disturbance in the electric and magnetic fields caused by accelerating electric charges. In quantum mechanics, a stream of photons. Light.
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period
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The time it takes for a regularly repetitive process to complete one cycle.
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wavelength
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The distance on a wave between two adjacent points having identical characteristics. The distance a wave travels in one period. Unit: meter.
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spectrum (pl. spectra)
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1. The intensity of electromagnetic radiation as a function of wavelength. 2. Waves sorted by wavelength.
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micrometer ( m)
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Also called micron. 10-6 meter; a unit of length used for the wavelength of electromagnetic radiation.
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nanometer (nm)
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One billionth (10-9) of a meter; a unit of length used for the wavelength of light.
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electromagnetic spectrum
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The spectrum made up of all possible frequencies or wavelengths of electromagnetic radiation, ranging from gamma rays through radio waves and including the portion our eyes can use.
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ultraviolet (UV) radiation
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Electromagnetic radiation with frequencies and photon energies greater than those of visible light but less than those of X-rays, and wavelengths shorter than those of visible light but longer than those of X-rays.
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X-ray
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Electromagnetic radiation having frequencies and photon energies greater than those of ultraviolet light but less than those of gamma rays, and wavelengths shorter than those of UV light but longer than those of gamma rays.
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gamma ray
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Electromagnetic radiation with higher frequency, higher photon energy, and shorter wavelength than all other types of electromagnetic radiation.
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infrared (IR) radiation
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Electromagnetic radiation with frequencies and photon energies occurring in the spectral region between those of visible light and microwaves.
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microwave radiation
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Electromagnetic radiation with frequencies and photon energies occurring in the spectral region between those of infrared radiation and radio waves.
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radio wave
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Electromagnetic radiation in the extreme long-wavelength region of the spectrum, beyond the region of microwaves.
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photoelectric effect
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An effect whereby electrons are emitted from a substance illuminated by photons above a certain critical frequency.
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photon
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Also called quantum of light. A discrete unit or particle of electromagnetic radiation. The energy of a photon is equal to Planck's constant (h) multiplied by the frequency (f ) of its electromagnetic radiation: Ephoton = h x f. The photon is the particle that mediates the electromagnetic force.
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Planck's constant (h)
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The constant of proportionality between the energy of a photon and the frequency of the photon. This constant defines how much energy a single photon of a given frequency or wavelength has. Value: h = 6.63 x 10-34 joule- second.
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intensity (of light)
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The amount of radiant energy emitted per second per unit area. Units for electromagnetic radiation: watts per square meter (W/m2).
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quantized
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Describing a quantity that exists as discrete, irreducible units.
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quantum mechanics
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The branch of physics that deals with the quantized and probabilistic behavior of atoms and subatomic particles.
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matter
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1. Objects made of particles that have mass, such as protons, neutrons, and electrons. 2. Anything that occupies space and has mass.
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atom
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The smallest piece of a chemical element that retains the properties of that element. Each atom is composed of a nucleus (neutrons and protons) surrounded by a cloud of electrons.
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nucleus (pl. nuclei)
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1. The dense, central part of an atom. 2. The central core of a galaxy, comet, or other diffuse object.
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proton (p or p+)
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A subatomic particle having a positive electric charge of 1.6 x 10-19 coulomb (C), a mass of 1.67 x 10-27 kilograms (kg), and a rest energy of 1.5 x 10-10 joules (J).
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neutron
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A subatomic particle having no net electric charge, and a rest mass and rest energy nearly equal to that of the proton.
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electron (e-)
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A subatomic particle having a negative charge of 1.6 x 10-19 coulomb (C), a rest mass of 9.1 x 10-31 kilograms (kg), and mass-equivalent energy of 8 x 10-14 joules (J). The antiparticle of the positron.
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Bohr model
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A model of the atom, proposed by Niels Bohr in 1913, in which a small positively charged nucleus is surrounded by orbiting electrons, similar to a miniature solar system.
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Heisenberg uncertainty principle
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The physical limitation that the product of the position and the momentum of a particle cannot be smaller than a well-defined value, Planck's constant (h).
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momentum
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The product of the mass and velocity of a particle. Units: kilograms times meters per second (kg m/s).
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ground state
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The lowest possible energy state for a system or part of a system, such as an atom, molecule, or particle.
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excited state
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An energy level of a particular atom, molecule, or particle that is higher than its ground state
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decay
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1. The process of a radioactive nucleus changing into its daughter product. 2. The process of an atom or molecule dropping from a higher-energy state to a lower-energy state.
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emission
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The release of electromagnetic energy when an atom, molecule, or particle drops from a higher-energy state to a lower-energy state.
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emission line
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An intensity peak in a spectrum that is due to sharply defined emission of electromagnetic radiation in a narrow range of wavelengths.
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absorption
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The capture of electromagnetic radiation by matter.
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absorption line
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An intensity minimum in a spectrum that is due to the absorption of electromagnetic radiation at a specific wavelength determined by the energy levels of an atom or molecule.
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density
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The measure of an object's mass per unit of volume. Units: kilograms per cubic meter (kg/m3).
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Doppler effect
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The change in wavelength of sound or light that is due to the relative motion of the source toward or away from the observer.
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rest wavelength
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The wavelength of light we see coming from an object at rest with respect to the observer.
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blueshift
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The Doppler shift toward shorter wavelengths of light from an approaching object.
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redshift
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Also called Doppler redshift. The shift toward longer wavelengths of light by any of several effects, including Doppler shifts, gravitational redshift, or cosmological redshift.
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Doppler shift
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The amount by which the wavelength of light is shifted by the Doppler effect.
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radial velocity
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The component of velocity that is directed toward or away from the observer.
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static equilibrium
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A state in which the forces within a system are all in balance so that the system does not change.
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unstable equilibrium
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An equilibrium state in which a small disturbance will cause a system to move away from equilibrium.
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dynamic equilibrium
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A state in which a system is constantly changing but its configuration remains the same because one source of change is exactly balanced by another source of change.
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stable equilibrium
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An equilibrium state in which the system returns to its former condition after a small disturbance.
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thermal energy
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The energy that resides in the random motion of atoms, molecules, and particles, by which we measure their temperature.
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thermal equilibrium
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The state in which the rate of thermal-energy emission by an object is equal to the rate of thermal-energy absorption.
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equilibrium
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The state of an object in which physical processes balance each other so that its properties or conditions remain constant.
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temperature
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A measure of the average kinetic energy of the atoms or molecules in a gas, solid, or liquid.
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kinetic energy (EK)
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The energy of an object due to its motions. EK = 1/2 mv2. Units: joules (J).
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thermal motion
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The random motion of atoms, molecules, and particles that gives rise to thermal radiation.
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continuous radiation
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Electromagnetic radiation with intensity that varies smoothly over a wide range of wavelengths.
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thermal radiation
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Electromagnetic radiation resulting from the random motion of the charged particles in every substance.
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power
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The rate at which work is done or at which energy is delivered. Unit: watts (W) or joules per second (J/s)
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watt (W)
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A measure of power. Units: joules per second (J/s).
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luminosity
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The total flux emitted by an object. Unit: watts (W).
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brightness
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The apparent intensity of light from a luminous object. Brightness depends on both the luminosity of a source and its distance. Units at the detector: watts per square meter (W/m2).
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blackbody
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An object that absorbs and can reemit all electromagnetic energy it receives.
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Planck spectrum
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Also called blackbody spectrum. The spectrum of electromagnetic energy emitted by a blackbody per unit area per second, which is determined only by the temperature of the object.
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Stefan-Boltzmann law
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The law stating that the amount of electromagnetic energy emitted from the surface of a body, summed over the energies of all photons of all wavelengths emitted, is proportional to the fourth power of the temperature of the body.
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flux
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The total amount of energy passing through each square meter of a surface each second. Units: watts per square meter (W/m2).
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Stefan-Boltzmann constant
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The proportionality constant that relates the flux emitted by an object to the fourth power of its absolute temperature. Value: 5.67 x 10-8 W/(m2 K4) (W = watts, m = meters, K = kelvin).
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Wien's law
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A relationship describing how the peak wavelength, and therefore the color, of electromagnetic radiation from a glowing blackbody changes with temperature.
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albedo
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The fraction of electromagnetic radiation incident on a surface that is reflected by the surface.
