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Key Terms

any object that absorbs radiation
absorption spectrum
wavelengths of absorbed radiation by atoms and molecules
Balmer formula
describes the emission spectrum of a hydrogen atom in the visible-light range
Balmer series
spectral lines corresponding to electron transitions to/from the n=2n=2 state of the hydrogen atom, described by the Balmer formula
perfect absorber/emitter
blackbody radiation
radiation emitted by a blackbody
Bohr radius of hydrogen
radius of the first Bohr’s orbit
Bohr’s model of the hydrogen atom
first quantum model to explain emission spectra of hydrogen
Brackett series
spectral lines corresponding to electron transitions to/from the n=4n=4 state
Compton effect
the change in wavelength when an X-ray is scattered by its interaction with some materials
Compton shift
difference between the wavelengths of the incident X-ray and the scattered X-ray
Compton wavelength
physical constant with the value λc=2.43pmλc=2.43pm
cut-off frequency
frequency of incident light below which the photoelectric effect does not occur
cut-off wavelength
wavelength of incident light that corresponds to cut-off frequency
Davisson–Germer experiment
historically first electron-diffraction experiment that revealed electron waves
de Broglie wave
matter wave associated with any object that has mass and momentum
de Broglie’s hypothesis of matter waves
particles of matter can behave like waves
double-slit interference experiment
Young’s double-slit experiment, which shows the interference of waves
electron microscopy
microscopy that uses electron waves to “see” fine details of nano-size objects
emission spectrum
wavelengths of emitted radiation by atoms and molecules
any object that emits radiation
energy of a photon
quantum of radiant energy, depends only on a photon’s frequency
energy spectrum of hydrogen
set of allowed discrete energies of an electron in a hydrogen atom
excited energy states of the H atom
energy state other than the ground state
Fraunhofer lines
dark absorption lines in the continuum solar emission spectrum
ground state energy of the hydrogen atom
energy of an electron in the first Bohr orbit of the hydrogen atom
group velocity
velocity of a wave, energy travels with the group velocity
Heisenberg uncertainty principle
sets the limits on precision in simultaneous measurements of momentum and position of a particle
Humphreys series
spectral lines corresponding to electron transitions to/from the n=6n=6 state
hydrogen-like atom
ionized atom with one electron remaining and nucleus with charge +Ze+Ze
inelastic scattering
scattering effect where kinetic energy is not conserved but the total energy is conserved
ionization energy
energy needed to remove an electron from an atom
ionization limit of the hydrogen atom
ionization energy needed to remove an electron from the first Bohr orbit
Lyman series
spectral lines corresponding to electron transitions to/from the ground state
nuclear model of the atom
heavy positively charged nucleus at the center is surrounded by electrons, proposed by Rutherford
Paschen series
spectral lines corresponding to electron transitions to/from the n=3n=3 state
Pfund series
spectral lines corresponding to electron transitions to/from the n=5n=5 state
in a circuit, current that flows when a photoelectrode is illuminated
photoelectric effect
emission of electrons from a metal surface exposed to electromagnetic radiation of the proper frequency
in a circuit, an electrode that emits photoelectrons
electron emitted from a metal surface in the presence of incident radiation
particle of light
Planck’s hypothesis of energy quanta
energy exchanges between the radiation and the walls take place only in the form of discrete energy quanta
postulates of Bohr’s model
three assumptions that set a frame for Bohr’s model
power intensity
energy that passes through a unit surface per unit time
propagation vector
vector with magnitude 2π/λ2π/λ that has the direction of the photon’s linear momentum
quantized energies
discrete energies; not continuous
quantum number
index that enumerates energy levels
quantum phenomenon
in interaction with matter, photon transfers either all its energy or nothing
quantum state of a Planck’s oscillator
any mode of vibration of Planck’s oscillator, enumerated by quantum number
reduced Planck’s constant
Planck’s constant divided by 2π2π
Rutherford’s gold foil experiment
first experiment to demonstrate the existence of the atomic nucleus
Rydberg constant for hydrogen
physical constant in the Balmer formula
Rydberg formula
experimentally found positions of spectral lines of hydrogen atom
scattering angle
angle between the direction of the scattered beam and the direction of the incident beam
Stefan–Boltzmann constant
physical constant in Stefan’s law
stopping potential
in a circuit, potential difference that stops photocurrent
wave number
magnitude of the propagation vector
wave quantum mechanics
theory that explains the physics of atoms and subatomic particles
wave-particle duality
particles can behave as waves and radiation can behave as particles
work function
energy needed to detach photoelectron from the metal surface
doubly ionized helium atom
beam of αα-particles (alpha-particles)
beam of electrons
beam of highly energetic photons
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