Key Terms

Key Terms

absorber

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 $n=2$ state of the hydrogen atom, described by the Balmer formula

blackbody

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 $n=4$ 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 ${\lambda }_c=2.43\text{pm}$

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

emitter

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 $n=6$ state

hydrogen-like atom

ionized atom with one electron remaining and nucleus with charge $+Ze$

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 $n=3$ state

Pfund series

spectral lines corresponding to electron transitions to/from the $n=5$ state

photocurrent

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

photoelectrode

in a circuit, an electrode that emits photoelectrons

photoelectron

electron emitted from a metal surface in the presence of incident radiation

photon

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 $2\pi \text{/}\lambda$ 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 $2\pi$

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

$\alpha$-particle

doubly ionized helium atom

$\alpha$-ray

beam of $\alpha$-particles (alpha-particles)

β-ray

beam of electrons

γ-ray

beam of highly energetic photons